Growing Trees and Shrubs in Warm Places
TREES & SHRUBS FOR WARM PLACES When you grow plants in a Tropical, Sub Tropical or artificially heated environment, there are a lot of things that need to be approached in a different way.
Many of our most magnificent gardens can be found in hot places. The range of plants available for such situations, provide a palette of unique textures, colours and shapes.
The heat, and humidity in moister areas, encourages diversity of plant life. With the right approach, and careful selection of plants, a hot place can be turned into a very livable garden.
Plants in fact can help modify the temperature in a hot place. Large plants not only shade the ground below keeping it cooler; but will keep the temperature lower by not trapping and radiating heat in the same way as other surfaces, such as rock, paving, metal or glass. Plants also lower temperatures in their immediate vicinity through the release of water vapour from their foliage during photosynthesis.
This book is relevant to gardens in tropical and subtropical climates; and to hot places in cooler climates such as: growing in Greenhouses; "heat trap" courtyards; and arid sites.
What Causes An Area To Be Warm?
There are a number of things which contribute to a garden space becoming hot.
Most heat will come directly from the sun. Generally the closer an area is to the equator the warmer it is
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The average maximum daily temperature will generally increase the further you move away from coastal areas. The sea or ocean has a temperature moderating effect. Temperature also decreases as altitude increases, so even in tropical regions high altitude sites will normally be significantly cooler than adjacent lowland sites. Some coastal areas may also remain warmer than other areas at the same latitude (distance from the equator) due to the presence of warm ocean currents.
Cloud cover has an effect on air temperature near the earth's surface, by keeping it cooler in the day, but warmer at night as warmth cannot escape the atmosphere.
Existing vegetation can dramatically modify temperature over a large land area. Vegetation will buffer the temperatures by keeping air slightly warmer in winter and cooler in summer.
Some materials will absorb and/or store, and radiate heat more than others. Materials such as metal, stone, glass, and paved areas can contribute to increased heat in a garden. The more these materials are used, the more likely the garden is to warm up, and stay warm. Heat can also be generated (to a lesser extent) by human activity such as burning off, factories, motor cars, etc. Factors such as these often mean that temperatures in a city are likely to be higher than in the surrounding countryside.
Plants and animals have biological mechanisms which help cool their tissues. This biological cooling can in fact contribute to cooling a garden. By increasing the biological mass within a garden, you will tend to decrease high temperatures. Lawns, for example, will keep an area much cooler than if the area was paved.
An increase in altitude (height above sea level) will usually result in a decrease in average maximum temperatures (approximately a decrease of 0.6 degree Centigrade per100 metre increase in altitude).
Any insulating material will also tend to reduce temperatures (e.g. wood furniture or paving will keep a garden space cooler than masonry or metal).
Good ventilation helps take heat from a garden (ie. if air can move freely through a garden, cool air will move in to replace hot air. Larger more open spaces allow better air flow.
Water is always useful in cooling an area. If the water can be splashed through the air (e.g. a waterfall or fountain), the cooling affect is increased.
Anything which blocks the radiation from the sun will create a cooling affect. This includes shade from trees, pergolas, shadecloth or anything else......
COMMON HOT GARDEN AREAS
When we think of hot gardens, our thoughts usually turn to the tropics or sub-tropics. Gardens in these areas are commonly hot; but not necessarily so. There are exceptions. Tall mountains in New Guinea can be covered with snow. Shaded rainforests in sub-tropical south-east Queensland can suffer at times from temperatures approaching zero degrees Centigrade. Desert areas, such as those found in central Australia, are generally regarded as hot/dry climates however night temperatures can easily reach zero degrees Centigrade or less in winter. And in cooler areas it is possible that a small paved courtyard garden may suffer higher temperatures than a shaded rainforest garden in the sub-tropics will ever face.
Tropical areas are those parts of the world that fall between the Tropics of Cancer & Capricorn, which are lines of latitude lying 23.5 degrees north and south, respectively, of the equator. The most highly populated parts of these areas are typically hot and humid most of the year, with a mainly dry period during the winter and a pronounced wet season during the summer period. Humidity becomes even higher during the rainy season. Many of these areas may also be subject to cyclones and severe storms. Some parts of the tropics however are drier, even deserts. These areas may also be subject to severe windstorms, but rainfall and humidity may be much lower.
Generally warm like the tropics, but conditions may be more seasonal. Temperature fluctuations may be greater than for tropical areas. Sub-tropical areas can suffer from frosts, particularly inland areas. They can also have very hot days. Subtropical climates can be generally described as areas outside the tropics which exhibit a few features similar to those found in the tropics. Areas outside the tropics can be described as zones south of the Tropic of Capricorn; and zones north of the Tropic of Cancer.
A greenhouse is simply a structure or building used to provide suitable growing conditions for particular plants that could not normally be grown, or could only be grown with difficulty, in the outside environment. Tropical plants are most commonly grown as greenhouse or indoor plants in cooler climates.
Hot spaces are sometimes created intentionally, and sometimes unintentionally, in cooler climates.
Poorly ventilated areas (e.g. a walled or fenced in garden space such as a courtyard), will not cool down as readily as more exposed sites, and can become a heat trap. Small, enclosed areas are more likely to act as a heat trap.
Walls which face the sun (e.g. north facing in the southern hemisphere), tend to heat up faster than walls not exposed to as much sunlight; and they then radiate heat back over the day into the adjacent garden.
Paving or concrete heats up much more than grass, and can also produce a lot of glare.
Large ponds or pools can have a moderating effect on the local temperature. As the water heats during the day from the effect of sunlight some will evaporate lowering the temperature in the immediate area. In addition some of the incoming heat will remain in the water to be radiated back into the atmosphere at night, once the sun has gone, helping to keep temperatures slightly warmer in the immediate area.
ARID AREAS (DESERTS & SEMI-DESERTS)
These can become very hot during the day; but also very cold at night. Many inland parts of Australia, Asia, America and Africa have low rainfall; and can be very hot - temperatures in the high 40's degrees Centigrade during the day, to near zero at night. Plants here must be hardy to extremes. Gardens in such areas should be designed to buffer extreme temperature fluctuations. Use of drought tolerant plants, and efficient water management can help in creating an attractive garden in such areas.
WARMING THE GARDEN
There may be reasons why an individual may wish to raise the temperature within the garden. One reason may be that they like warmth and heat as opposed to the cool or cold temperatures of winter. The gardener may however, see the advantage of raising the garden temperature as an opportunity for growing more tropical plants in their location.
The gardener must look carefully at their site, and assess which places are the warmest for placing the most cold sensitive plants. These sites may be facing north against a wall, in a garden protected from winter winds, or even in a glasshouse.
CULTIVATION OF TREES & SHRUBS IN WARM PLACES
Plants need to be treated differently in warm climates. The affect of temperature creates different growth responses to those seen in cooler areas.
These responses are generally seen as:
The warm climate also tends to encourage a greater amount of pests and disease problems. This is the result of extended breeding periods available to the pests. The higher humidity that occurs in many warm climates promotes fungal diseases. It is important to note that this should not be seen as a disadvantage. Warm climate plants have adapted to the climate and to the increased incidence of such pests and diseases. Damage is either resisted, overcome by abundant growth or tolerated by most plants. In affect, it is the plants not suited to the climate or the site that become most affected by the pests and diseases.
Warm climates may promote such excessive growth that plants may become weed-like and invasive. Lantanas, for example, grown in cooler areas are very ornamental and controllable, however when grown in warm climates they tend to become environmental weeds.
In humid warm climates, spacing can be critical for many plants. Tropical plants like humidity therefore appreciate close spacing so that nearby plants help to maintain a humid microclimate. However, if temperate plants are grown in warmer climates, this close spacing may lead to plant death due to increased humidity. By spacing these plants further apart, the ventilation will remove excess humidity and the plants should have a better chance of survival.
Spacing can also be used to reduce the incidence of diseases.
If plants are crowded too close, competition for sunlight, water and nutrients may lead to slowing down of plant growth. This may lead to poor plant health and attack by pests.
When spacing plants out in the garden, consider the natural spread of the plant and the overall appearance desired in the garden.
The soil is the foundation of any garden. A healthy soil will lead to a healthy garden and plants. The sign of earthworms is a good indicator as to the healthy of the soil.
Having the perfect soil to start with is pure luck. Most gardeners need to resort to methods to improve the soil. However, once the soil has been improved, plant growth will be better and the soil maintenance requirements will generally be less.
There are several ways to improve soils, and these include ‑
Adding sand to clay type soils to improve drainage. This is only practical for small areas as a lot of sand would be required to have a useful effect.
Adding clay to a sandy soil to improve it's ability to hold water and nutrients.
Adding organic matter to most soils, with the exception of very organic rich soils, such as peats. This will improve the soils water holding capacity; help improve the soils structure, and hence help improve it's drainage; add valuable nutrients; encourage the growth of soil microorganisms; and act as a buffer against sudden chemical or temperature changes in the soil which could damage plant roots.
Use of soil ameliorants:
Lime can be added to soils with a low (acid) pH to raise the pH to a suitable level. Most plants prefer a pH around 6.0 to 7.5.
Lime will also help improve the structure of clay soils.
Gypsum can be added to help improve the structure of clayish soils. This will not alter the pH to any great degree as would the application of lime.
Sulphur containing fertilizers (e.g. Ammonium sulphate, sulphur dust) can be added to soils to lower pH when the soil may be too alkaline to suit your plants.
Brandname products such as "Claybreaker" and "Claygon" can be added to help break up clayish soils to improve drainage and root penetration.
Wetting agents (such as "Saturaid", "Hydretain" and "Wettasoil") can be used to allow water penetration into non-wetting (hydrophobic) sands (these are sands where the water doesn't readily penetrate, but sits in puddles on the soil surface or runs away down slope).
Mulch is great for a garden. Mulch keeps plant roots cool in the heat and warm in the cold. It also slows weed growth, holds moisture in the soil, stops the ground getting muddy, helps minimise soil compaction and usually just makes things look neater. Organic mulches will also provide nutrients to the soil as they decompose, and help improve soil structure.
Different mulches have different characteristics, so think about which mulches are best for you, and choose the right one for the job at hand. The price of different mulch materials will vary considerably and is often connected with whether the mulch is a 'waste' product in your area, or is being transported from another area.
Mulches can be divided into two broad groups: Organic & Inorganic.
These mulches were at some point of time a living plant. Plant material is beneficial as it returns nutrients back to the soil, and often provides a natural look to the garden.
The main organic mulches used are:
Wood (chips, shavings & sawdusts)
Sugar Cane Waste/By-products
Other plant matter - compost, leaf litter, coconut fibre, rice hulls, straw, hay and paper.
Mulches derived from the timber and forest industry, such as wood chips, pine bark or wood shavings used to be considered as waste products and were often burnt to get rid of them. They may contain toxins which may inhibit plant growth therefore weathering for 2-4 months is recommended first to allow leaching of the toxins. Most timber/wood products will rob the soil of nitrogen (this is called nitrogen draw down) in the first few months so it is recommended that an application of a nitrogenous fertilizer be applied just to the mulch.
These mulches are not organic by source. The do not provide nutrients to the soil but still provide water conserving attributes, and include:
What about a combination of mulches?
Various mulches can be combined in a garden bed. If there is a section, which in wet weather has a lot of water running through it, then a heavy mulch can be used that will not be washed away, e.g. river pebbles. If the water flow is very heavy it may be worthwhile creating an artificial dry creek bed using river stone concreted in place combined with loose river stones. Adjoining this area leaf litter can be used. This is ideal for native plant landscape gardens, or rainforest gardens.
In selecting which mulch to use consider the following:
The weight of the mulch:- Will it blow away in the wind, be washed away in light rain or be dislodged easily by watering, will it slip if the garden bank or bed has a steep slope, is it easy to spread?
How long before it has to be replaced or topped up?
Is the mulch readily available?
How much does it cost?
Does it require some sort of edging to prevent it being dislodged?
Does it encourage the presence of any vermin or pests into the garden?
The depth of the mulch is important if the mulch is to be used to suppress weeds. If the mulch is laid too thinly then weeds will still germinate. 10cm (4 inches) is regarded as a good thickness for most weeds. More vigorous or persistent weeds may require a thicker mulch.
Increased weed control can often be obtained by placing a layer of newspaper over the ground surface, beneath your other mulching material. Overlap each newspaper to ensure that there are no gaps between them.
It is not recommended that you lay impermeable plastic sheeting under mulch as it prevents water penetrating, and the reduced flow of air into the soil may cause problems for your plants. It has also been reported as encouraging cockroaches and nutgrass.
Weed mat appears similar to black plastic, but is permeable allowing water penetration and the flow of air around the plant roots, while greatly reducing the amount of weed growth.
The main ways of providing nutrients to trees and shrubs are as follows.....
A/ Mixing straight (organic or inorganic) fertilizers into potting soil before plants are potted up; and following with applications of liquid fertilizers at regular intervals.
Soil which has such fertilizer incorporated into it must be used quickly (within a week or two of adding fertilizer). The fertilizer can leach out...or change form if left for any period.
B/ Placing fertilizers into the soil or on the soil surface at the base of the plants.
Frequency of feeding will depend upon the type of fertilizer being used and upon the characteristics of the soil with regard to leaching out or retaining the nutrients applied.
C/ Mixing slow release fertilizers such as Nutricote or Osmocote (pelleted slow release fertilizer) into the soil before potting a plant into a container.
The slow release fertilizer might or might not be sufficient to feed the plant for its entire life, depending on the type of plant (e.g. an annual or a perennial). Temperature and moisture can affect how quickly or slowly the fertilizer is used up. Some fertilizers do not work at all in cooler climates during the winter months, and should normally be used only in sub-tropical or tropical regions.
Any fertilizer mixed into a soil must be mixed thoroughly and evenly. If it is not mixed well it is possible burning of the roots may occur in the place where most of the fertilizer is located/concentrated.
D/ Applying slow release fertilizer to the base of an established plant.
This method is preferred by some because it allows flexibility to apply different types of fertilizers to different plants, and because it does not have the problem of having to ensure a thorough mixing of fertilizer in the soil/potting mix. It is important that the person doing this job does not over feed or under feed (a pinch is not good enough). Variations in the rate of feeding can cause variations in the growth habit and growth rate between plants.
E/ Using Liquid Fertilizers only, normally applied through either sprays or through a watering system.
Liquid feeding can vary from daily to only once every 5 or 6 weeks. There are arguments for both ways. The danger is that overfeeding can burn plants and underfeeding will not achieve the growth required. The rate of feeding must be calculated carefully, and the application of liquid feeds must be very precise (only intelligent and cautious people should ever undertake such an operation).
In the Wet Tropics, liquid fertilisers will be leached out of the soil or potting mixes very fast and will need frequent re-applications. Use a slow release fertiliser in this case.
Many liquid fertilisers can be used as a foliar spray, where the nutrients are absorbed directly through the plants foliage. Any nutrient that is washed off, or drips to the ground, is then available for the plant to absorb through it's roots.
Slow Release Fertilizers
With the availability of a wide range of slow release fertilizers on the market it is important to note that some have a better track record in warm climates compared to others. It has been shown from research that some types can break down in the heat of warm climates and drop most of their nutrients over a short period. Some types, however do not appear to have this problem. It is worthwhile obtaining product information leaflets when considering using these types of products that provide performance details for each product at different temperature and moisture conditions.
FACTORS AFFECTING FERTILIZER APPLICATION
Different plants will use fertilizers at different rates. Slow growing plants, for example, should be fed at lower rates compared to quicker growing plants. Plants will also require differing types and levels of nutrients at different stages of their growth (e.g. during active vegetative growth in comparison to setting fruit). This will also affect fertilizer type and quantities.
Fertilizer will wash through more sandy (better draining) soils, much faster than for other soil types, and should be applied more often and in smaller quantities on such soils.
The pH (acidity or alkalinity) of the soil affects the availability of different nutrients in different soils or mixes. If the pH is very acid (eg. pH 4) certain nutrients such as iron are readily available for plants, but others such as nitrogen, are not able to be taken up as easily as they are at a higher pH. Every nutrient has its own ideal pH. Different trees and shrubs require different amounts of different nutrients, and this fact makes it preferable to have the soil pH at different levels for different types of plants to achieve the optimum nutrient availability. Some things grow better at pH 5, others are better at pH 7; most prefer a pH around 5.5 to 6.5.
APPLICATION OF LIQUID FERTILIZERS
The simplest device to use is a standard chemical sprayer. Because of the quantity of plants being fed, the chemical is normally applied in a concentrated solution and immediately watered with normal irrigation to wash it off the leaves and into the soil (preventing burning of the leaves).
Many warm areas have very high rainfall. Depending on which plants you wish to grow poor drainage may sometimes be a problem. There are a number of ways to readily improve drainage, including:
Growing your plants in raised beds. Soil can be retained using materials such as timber, rocks and concrete.
Growing your plants on mounds. Drainage can be further improved by using builders rubble, old brick pieces, rocks, etc. to form the base of the mound, with sufficient soil placed on top to support plant growth.
Installing sub-surface drainage (e.g. slotted plastic agricultural drainage pipe).
Diverting surface runoff away from your garden by installing surface drains or diversion channels, or sloping the ground surface.
* Growing those plants that require good drainage in containers.
Time of Planting
Avoid planting on hot or windy days. Plants are more likely to dry out in these conditions.
If trees and shrubs are likely to get a lot of attention, they can be planted successfully at almost any time of year, however, if they are going to be neglected they are best planted prior to the cooler months; or wetter time of the year. If planting in warm areas where the wetter months are over summer, such as the northern parts of Australia, you can plant almost any time of the year as long as you provide sufficient moisture during dry periods, and good drainage during wet periods.
Availability of plants may influence planting time. If the plants are only available at one time of the year then the options are to plant immediately and take certain precautions to ensure their success; or look after the plant until the right planting time arrives. If planting immediately, take extra care when teasing out the roots before planting and shade the plant from excessive sun. Prune the plant lightly and keep it well watered.
Basic Planting Procedure
Plant most containerised plants as follows:
Thoroughly soak the plant in the pot ... to help the plant come out of the pot easier ... and allow it to drain.
Dig a hole one and a half times the depth of the pot, and at least two times the width of the pot. This is the minimum size that should be dug under ideal soil conditions.
Place fertilizer in the hole. The type of fertilizer will vary depending upon the climate of the area, but in most instances, a good slow release fertilizer is advisable.
Fill in one third of the hole and mix fertilizer with the back filled soil.
Carefully take the plant out of the pot.
Loosen any exposed roots. (i.e. If most of the roots are inside the soil ball, you might not need to do much. If there is a tight mass of roots on the outside of the soil ball you may need to break a centimetre or so into the ball all over). Free any roots circling the bottom.
Place the plant in the hole and cover with soil. Firm down.
Make a lip of soil the same diameter as the hole around the base of the plant to hold water.
Soak thoroughly with water.
Staking is not always necessary (it can in some cases do more harm than good). Plants SHOULD be staked if they are likely to fall over (perhaps because they are exposed to severe winds ... perhaps because they are loose in the soil). Plants might be staked to protect them from vandalism or unintentional damage (however consider that a stakes may draw attention to the plant and thereby attracting vandals). When you do tie a plant to a stake, the tie should be loose allowing the plant to move about in the wind, without excessive movement that could the plant trunk to break. If movement is restricted, the tree may never develop proper trunk strength. Staking is best carried out during the planting process, as staking later may damage the roots of an established plant.
Water is becoming an increasingly scarce and costly resource. Hence a well planned garden with appropriately selected trees and shrubs and an efficient watering system can play a major part in determining the size of the water bill. Designing and operating an effective watering system will be made easier by paying attention to the following when planning your garden.
As the tropics have a distinctive wet and dry season, watering during the wet season is rarely needed. In the dry season, many tropical trees have adapted to the lack of water by having a semi-deciduous stage. This reduces the tree’s need for large amounts of water. Other species may need additional watering during this period.
The best way to water plants is by delivering water to the roots. Options available include:
hollow piper fixed in the ground into which the water can be poured;
probes that connect to hoses that are pushed into the ground and force water into the surrounding soil under pressure;
drippers and micro sprinklers;
deep long periods of irrigation using conventional sprinklers.
1. Consider your climate and aspect when selecting plants. Try to choose those which are adaptable to your conditions. Plants chosen from different climatic regimes usually require much more attention and often lots of water to produce the desired effect (rainforest plants growing in an arid zone will need more water than plants adapted to arid conditions).
2. Soils vary greatly clays (which hold moisture) to sands (which drain freely). A sandy soil will therefore require more watering to satisfy the plant’s requirements. Clay soils generally need less. Due to the deeper root systems of trees and shrubs, it is essential to get the irrigation down to the roots. Clay soils generally require more water to ensure a thorough deep soaking compared to sandy soils. Use of water probes tends to overcome many of these problems.
3. The type and position of lawn areas contributes significantly to the overall water consumption in a garden. Select lawn species wisely and don't be afraid to let them dry out a little over the dry season ‑ lawn species have a remarkable ability to recover when the rains come.
4. Mulching is one of the best ways to minimise water use.
5. Keeping plants healthy (well fed and free from pests and diseases) allows them to make better use of the water applied ‑ therefore you will need less. Also do not leave too much exposed soil between plants. If the plants are reasonably close their foliage will shade the ground and minimise water evaporation.
6. Getting professional advice to assist in planning your garden and watering system can be an investment in future cost savings. Good advice is often available from suppliers and installers of irrigation equipment so take advantage of it.
The old fashioned method of watering gardens by sprinklers throwing water about fairly vigorously is out of favour in most smaller gardens. It is still popular in larger gardens and parks, but even there a lot of time is spent dragging hoses into position. There are two basic methods of watering efficiently using sprinkler systems. The more solid installed irrigation systems involving high pressure, high discharge watering, as is the case with pop‑up systems, are very useful over larger areas and with lawn. These are carefully organised, using different nozzles to throw out different water patterns, so that all areas are covered with minimal amount of water being wasted on paths, or over watering.
The second efficient method of watering is micro-irrigation. This can be via trickle irrigation or by using microsprays. These methods can ensure water is delivered to only where it is needed. It needs only low pressure and discharge is slow so that water is able to soak (infiltrate) into the soil therefore avoiding puddling or runoff.
Several points should be remembered when selecting which equipment to use.
Drippers are more suited:‑
To watering individual plants such as potted plants and isolated trees and shrubs.
They are excellent for heavy clay soils where water penetration is slow.
The concentrated wetting pattern they provide means they are better on severe slopes (located up the slope from the plant).
They are preferable for plants which may suffer from fungus diseases, such as powdery mildew, when they are watered from above.
They will still work when water pressure is extremely low.
They help keep weeds down as less surface area of soil is damp enough for seed germination.
Microsprays can either be spray jets discharging a course to fine spray or sprays which discharge the water in streams or fingers. Both are suited to:‑
Fitting into any garden shape with a variety of watering patterns and flow rates available.
Free draining soils where water infiltration rates are fairly high. They are also generally better for shallow rooted ornamentals, shrubs and annuals.
Other types of irrigation available are Misters (used to increase humidity) and Rotor sprays for larger areas.
Once all this information is taken in to consideration you should be able to tell what is needed where and how much equipment you will need to buy. Remember that you will have to install different lines if you want to use both drippers and sprays, as they work on different pressures, though they can be connected to the same tap using two shut off valves and a tee piece.
High Discharge Irrigation
Irrigation for large areas and lawn requires a high discharge rate, requiring a high water pressure. Installing these systems can be rather complicated as it necessary to work out total discharge of all sprinklers required and choose suitable width pipes to provide the necessary pressure. As it is important that all sprinklers receive the same pressure, solenoid or gate valves may need to be incorporated to balance the system. These difficulties are most relevant when considering very large areas. A pop‑up system in a domestic lawn will often be comparatively easy to install as long there are not too many sprinklers required.
Other Watering Systems
Most other watering systems require more manual labour, mostly the moving round of hoses to appropriate places. Water is discharged using a wide variety of sprinklers which can vary in the area they cover and the droplet size produced. Sprinklers that rotate are better on heavier soils as they allow water to penetrate and reduce run‑off, or slow applications, as with soaker hoses are also good. Free draining soils such as sandy soils will cope better with continuous heavy applications. Watering cans still have their place, as they are ideal for giving a set amount of water to an individual plant.
Water probes are highly advantageous to trees and shrubs but need to be manually moved from place to place and pushed into the ground. These are then left in the one place for a predetermined time before moving them to the next location. Water probes may reduce the incidence of disease as they do not wet foliage or increase humidity. Some brands have the added advantage of allowing liquid fertilizer to be applied at the same time.
There are now available a wide range of automotive systems which work either by using clockwork or computers. Ranging in function and price you can obtain systems which simply allow the water to flow for a certain amount of time once you have turned it on, to systems which work independently by utilising equipment which measures moisture in the soil or air.
WHEN TO WATER
To minimise water wastage, watering at the most suitable time and in the proper manner is a must. Firstly you should consider how much watering needs to be done according to the types of plants and soil present. If you have a garden with plants that prefer arid conditions frequent watering will not be as necessary as it is for a rainforest garden. Observe your plants and see how long they last before they start showing signs that watering is necessary. Trees and shrubs suffering lack of water may show signs such leaf wilt, leaf yellowing, leaf burning and stunted growth, though it is not recommended to wait for such symptoms to occur. Over watering can result in soft, lush, leggy growth with few flowers or fruit and a susceptibility to disease. Too much watering will leach nutrients from the soil.
Also observe your soil, a free draining sandy soil with delicate ornamentals may need watering up to twice a day in dry weather, while a heavier clay soil which holds a lot of water may require watering once every three days. Do not water on a strictly regular basis: make sure it is needed.
The time and manner of watering should also be considered. It is generally much better to water more thoroughly, less frequently, as this will encourage deeper roots and make the plant less susceptible to dry periods, though there are plants which are naturally shallow rooted and require more frequent watering. Do not water during the heat of the day, as much of the moisture will be evaporated into the air and top layer of warm soil. It is much better to water in the evening or early morning. If you have an automated system with a timer, watering in the middle of the night is a good idea, particularly with large irrigation systems, as the water pressure is usually better then. Evening and night watering though can produce mildew as the leaves stay wet for a long period. This may not be a issue when growing glossy leafed species such as Gardenias, but can be a big problem when growing species such as Azaleas which have hairy, water attracting leaves. When timing your watering according to the weather, it must be kept in mind that a windy day can be more drying than a windless, hot day, and that long periods of cloud cover do not mean that the soil is not drying out ‑ plants still drink up water whether the sun is shining or not.
PESTS & DISEASE PROBLEMS
Plants can get sick just as easily as people.
The problems they encounter can include:
PESTS......Animals of various sizes and forms (from microscopic worms to dogs, birds, grazing animals, even humans). Insects are just one of many groups of animals which can cause damage to trees and shrubs, although they are perhaps the most significant group of plant pests.
DISEASES...These are problems caused by living organisms other than animals. Fungi, bacteria and viruses are the most common.
ENVIRONMENTAL DISORDERS....Troubles caused by soils, nutritional problems, bad weather conditions such as frost, wind, cold, and heat.
WEEDS......Plants growing where you don't want them. It is the location of a plant which makes it a weed, NOT the species of the plant. A weed will compete with your desired plants for nutrients, water, space, light etc., and as such can be harmful to your desired species.
PREVENTATIVE MEDICINE IN THE GARDEN
The best way to be sure that problems like those outlined above do not occur in the garden is to prevent problems from ever starting in the first place.
This is best done by following the procedures listed below:
1. CONSIDER THE SITE
Does it have any particular problems which should be treated?
Poor soil conditions.
Winds...provide wind breaks or channel winds with fences or plantings.
Shade...large existing trees, buildings, etc. can create very shady areas. In such areas select plants to grow that will tolerate or even prefer periods of shade.
Frost pockets...on sloping sites remove a frost pocket by planting or fencing in a way that allows air movement to continue unimpeded down the slope.
Other soil problems, such as low nutrient levels, or diseases may have built up (particularly where the same type of plant has been grown in a particular spot year after year), or the soil may be full of a mat of dead roots, etc.
2. BUILD UP THE SOIL
Before you even start a new garden, make sure the soil is in top condition. Make sure drainage, nutrition, friability, etc. is suitable for the plants you wish to grow.
This may involve laying drainage pipes, applying fertilizers, gypsum or lime, or digging in manure & compost. Kill existing soil pests if necessary.
3. USE HEALTHY PLANTS/SEEDS
Healthy plants are more likely to resist damage from pests and diseases, and more likely to recover if they are attacked. The roots and top growth of the plant should be well developed. There should be no deformed growths (eg: twisted, distorted leaves, swellings on roots). Avoid plants with badly marked leaves. Don't use plants contaminated with insects. Seeds and bulbs should be fresh, free of abnormal markings or any rots. Prefer
4. MAINTAIN CLEANLINESS
Remove any diseased fruit, flowers, leaves, etc. and burn (do not compost them or let them lay on the ground!). Wash soil off paths, concrete areas, etc. Soil tracked from one area to another may spread disease. Sit plants in containers on stones or paving, or on top of a couple of bricks (not directly on top of soil). This minimises movement of disease from the soil up into the pot.
5. MAINTAIN THE NUTRITION & WATER NEEDS OF THE PLANT
Do not over water or underwater...both are as bad as each other! Over watering (waterlogging) is indicated by yellowing of the lower leaves, sometimes wilting and eventually dropping of the lower leaves. Underwatering is indicated by browning of the tips and foliage generally, and at times by severe wilting and leaf drop.
Lack of nutrients is indicated by a slow rate of growth, and in severe cases, by discolouration patterns on the leaves.
6. INSPECT PLANTS REGULARLY AND ACT AS SOON AS A PROBLEM IS DETECTED
Look at tips first. The young growth will indicate general vigour (or lack of it). Look for die‑back, discolouration of leaves or wood, distortion of growth, rots, eaten or broken tissue, etc.
PEST PROBLEMS ON PLANTS
Before using any of the controls suggested here make sure that they are available in your area, and that their use is allowed. (Availability and appropriateness of chemicals can vary greatly from place to place. The following is nothing more than a general guide at the time this was written).
APHIDS ‑ Many different types, 1‑4mm (0.004 - 0.016 in) long, in various colours, most commonly green. They sit on soft plant tissue with a syringe like mouthpiece injected into the plant tissue sucking nutrients, etc. out of the plant. They can transfer virus or other diseases from plant to plant. Aphids may cause twisting and malformations of new growth. They are normally found in colonies comprising dozens to thousands of individuals. Aphids are most likely to attack the more tender tissue on shoot tips, leaves or stems. They can also attack bulbs and roots.
CONTROL: Natural‑use biological controls such as ladybirds & other antagonistic insects, or use a garlic spray. Chemical‑spray with Pyrethrum or Malathion.
AZALEA LACE BUGS - Sap sucking insects common on Rhododendrons and Azaleas. The adults are 4-5mm long, shiny black in colour, and have lace-like wings. Their eggs are usually laid along larger leaf veins or stuck hard to the leaf surface. The young have dark brown spines sticking out from the sides of their bodies. They cause mottled white and silvery grey markings on the leaves, and can seroisly affect the vigour of the plant.
CONTROL: Spray with asecticide such as Rogor or Lebaycid, and maintain plant vigour through good watering and fertilising practices.
BEETLES - These insects eat leaves thereby partially or completely defoliating trees and shrubs. Range in sizes from less than 1cm (0.4 in) to a few centimetres, in a range of colours. All are considered pests to the home gardener. Twig Girdler beetles are most active in warm summer and autumn seasons in the tropics and subtropics and cause the death of limbs by girdling branches.
CONTROL: Natural - use biological control- let birds and other creatures eat them, or remove them by hand. Chemical- use organic sprays such pyrethrum, or man-made chemicals such as Carbaryl, Malathion, Rogor or Mavrik. No control method is registered for girdler beetles.
BLACK SCALE (see Scale)
BORER ‑ These are grubs, which bore out cavities inside the stems of plants, or the wood of trees. Evidence is often found in the form of entry holes and the castings of dust/woodshavings around these holes. You may also see the borer itself if you cut away a section of the plant.
CONTROL: Natural‑remove the infected parts and burn. Chemical‑use a systemic insecticide containing such chemicals as Dimethoate or Omethoate.
BROWN OLIVE SCALE (see Scale)
CASE MOTHS (see Caterpillars)
CATERPILLAR ‑ There are many different types of caterpillars which normally eat the more tender parts of a plant (leaves and young shoots). Some cluster together in colonies as one ball of crawling grubs. Most caterpillars, however are solitary, each one crawling around independent of the others. Palms, climbers and bulbous tropical plants are often attacked by caterpillars. Note: all caterpillars produce either butterflies or moths.
CONTROL: Natural‑Spray with Dipel (a commercially available preparation containing a bacteria (Bacillus thuringiensis) which kills only caterpillars). Remove by hand. Chemical‑Spray with chemicals such as Malathion, Pyrethrum or Carbaryl.
CABBAGE WHITE BUTTERFLY ‑ These lay lemony yellow bullet shaped eggs on virtually all plants in the cabbage family (e.g. Cabbage, Cauliflower, Broccoli, Sprouts, Turnip, Radish, Kale...and weeds like wild radish mustard & winter cress). The caterpillars of this butterfly eat leaves, cauliflower heads, etc.
CONTROL: Natural‑Companion plants such as onion or garlic will help repel this pest, or spray with a Bacillus thuringiensis preparation (see entry on caterpillars). Chemical‑Malathion, Pyrethrum, Derris or Carbaryl.
CHAFER GRUB ‑ A thick white grub with dark coloured head that burrows in soil and feeds on organic material. It is also called a cockchafer and it is the grub of a beetle. It can cause severe root damage and sometimes death of smaller herbaceous plants such as chrysanthemums and grasses. The damage done to roots of trees and shrubs may weaken the vigour of the plants and reduce uptake of water and nutrients.
CONTROL: Natural – Encourage birds and other animals into the garden to hunt for the grubs. Chemical‑ Disyston or Malathion drench.
Some success has been achieved with lawn grub chemicals and carbaryl although they are not registered for this type of insect control.
CHINESE ROSE BEETLE - (see Beetles)
COTTONY CUSHION SCALE - Usually controlled naturally by Rodolia ladybirds. If spraying is required use white oil or maldison (e.g. Malathion). Avoid repeat applications of white oil as the plant may be damaged.
CRICKET ‑ The common field cricket has a dark brown body about 1 inch (2.5cm) long. It feeds on new tender plant growth.
CUTWORMS - (treat as for caterpillars)
ERINOSE MITE (see Mites)
FRUIT FLY - Generally brownish in colour with a small yellow band on their abdomen. The larvae (maggots) of this fly can attack a wide variety of fruits, including peaches, citrus, tomatoes, and bananas. In most Australian states control of this pest is compulsaory, and some states (e.g. Victoria) require notification to agricultural authorities of any outbreaks.
CONTROL: Quarantine laws in most Australian states prohibit the movement of fruit from known fruit fly areas to non-infected areas. Spraying with sysyemic sprays such as Rogor or Lebaycid. Destroy all infected fruit (e.g. burn) - do not place the fruit into compost heaps. This encourages their development.
FRUIT SPOTTING BUG - Most commonly attacks cultivated plants near areas of bushland. The adults are green, about 1.5cm long, the young (nymphs) have reddish black legs a darker reddish bdomen with two black spots. Both adults and young can cause serious damage by sucking sap. They can cause serious damage to Macadamia nuts.
CONTROL: Chemical - Spray with trichlorfon based sprays.
GRASSHOPPERS - Some are solitary, some appear in plague numbers, particularly in warm climates in warm seasons. They can completely denude a garden, attacking a wide rangee of plants. They lay eggs in the soil.
CONTROL: Encourage natural predators (e.g. birds, lizards, frogs). Spray with carbaryl or Lebaycid.
GRUBS (see Caterpillars)
HIBISCUS BEETLE - An oval shaped beetle, dullish-black in colour to about 3-4mm long. It mainly feeds on pollen, and can be founf in large numbers in Hibiscus flowers. It may sometimes chew holes in petals.
CONTROL: Controlled by natural predators in most cases. In severe infestations spray with a an endosulfan based preparation, but don't spray when bees are present as these can be seriously affected.
LEAF CHEWING INSECTS - Insects that chew plant tissue rather than suck out plant sap. Common examples include beetles, grasshoppers, caterpillars, and leaf miners.
LEAF HOPPERS - Small insects which jump when disturbed. They are sap suckers, and often leave shiny, sticky sap deposits on branches. They may cause distortion of leaves and/or shoots. Severe cases may cause wilt and dieback.
CONTROL: Encourage natural predators such as lizards, birds, ladybirds, and spiders.
Spray with pyrethrum based sprays for mild infestations, or a systemic such as Folimat or Lebaycid for severe infestations.
LEAF SUCKING INSECTS - Insects that suck the sap fronm plants, usually from the leaves and soft new growth, generally resulting in reduced vigour of the affected plant. These types of insects may also act as vectors (transporting agents) of virus diseases that can seriously affect the plants health. Common examples include aphids, thrip, scale, lerps, and whitefly.
LEAF MINER ‑ A small insect that eats long winding tunnels between the surfaces of leaves. Normally tunnels are white first, but turn brown later. This group of pests can attack a very wide variety of plants. Leaf minor are more commonly noticed on Citrus and Murraya shrubs.
CONTROL: Natural‑Remove infected parts & burn. Chemical‑Dimethoate or Omethoate.
LERPS - Also called Psyllids, these are small sap sucking insects. Lerps are a type of Psyllid that live beneath a protective waxy covering in the same way that scales do. They attack mainly Australian native plants, sucking out the sap, resulting in reddish brown and yellow blotches on the leaves, which eventually turn brown. Severe infestations can result in major leaf drop, and diebak of branches.
CONTROLS: Naturally controlled in most cases by predatory insects and birds. In severe cases spraying with a systemic insecticide such as Folimat or Rogor may be necessary, or for large trees direct injection into the tree of one of these chemicals may be required.
MACADAMIA FLOWER CATERPILLAR - (see Caterpillars)
MACADAMIA LEAF MINER (see Leaf Miners)
MACADAMIA NUT BORER (see Borers)
MANGO STONE WEEVIL (see Weevils)
MEALY BUG ‑ The adults resemble a slater covered with white waxy powder & waxy cotton‑like threads. They are generally 5‑20mm (0.2 – 0.8 in) long, can live on roots, under bark, and can move about on a plant according to seasonal conditions. This pest is a significant problem on topical indoor plants, palms, tropical shrubs and many ornamental plants. Mealybugs are related to Scale Insects.
CONTROL: Natural‑spray with a strong stream of water to dislodge the insects from the plant, or touch insects with a swab of cotton wool dipped in alcohol. Chemical‑White oil sprayed directly on insects, or Dimethoate.
MITE...See also Red Spider
Small, eight-legged animals related to spiders, which feed on a variety of plant and animal materials. A common type is Erinose mite, which sucks nutrients directly out of the leaves and veins of plants. It causes slight discolouration and twisting of the leaves. Fury-like structures appear on the underside of the leaves which indicate their appearance - this is often mistaken for rust disease. A range of tropical fruit trees (eg. lychee) and ornamental trees are prone to this pest.
CONTROL: Natural - none reported to work adequately to control problem. Chemical - use of miticides, Rogor and lime sulphur sprays have been used. Ensure chemical is registered for use in your area, and for the particular plant before applying.
NEMATODES - These are small, normally microscopic worms, which attack plant tissue, commonly roots. They cause distortion in growth, yellowing or dead patches, dwarfing of the plant, and dieback.
CONTROL: The best control is prevention - only obtain plants from reputable suppliers who use sterilized potting mixes, or sterilise soils from areas suspected of being infected with pest nematodes before using. Chemical nematicides, such as Nemacur can be used to treat infected plants.
PSYLLIDS (see Lerps)
RED SPIDER – Red spiders are mites, almost invisible to the naked eye, that appear as a red haze, usually on the back of leaves. Leaves can turn a bronze colour & die. It is common on azaleas, camellias, and many other ornamental plants.
CONTROL: Natural‑ Introduce predatory Spider Mites to the garden. Use repellent plants such as onion, garlic & chives. Chemical‑ Kelthane, Derris, Malathion.
RINGBARK BEETLE (see beetles)
SAWFLIES - A type of caterpillar. Prune off and destroy infested branches or spray as for caterpillars.
SCALE - These are small, shield‑like insects which fix themselves to a part of a plant and insert their mouthpiece into the plant. They remain in the one spot, and do not move. They are related to mealy bug. Colours include red, black, brown...etc. They generally attack leaves, soft stems and roots. Thes insects suck sap from the plants which may lead to tissue deformations and poor flowering. They are common on Hibiscus, Ixora, Gardenia, etc.
CONTROL: Natural – encourage predatory wasps and insects to control scale. Chemical ‑Malathion, Dimethoate, White Oil (must get direct contact).
SLATER ‑ Also called woodlice, they live in shady places, often moist, under stones, amongst mulch, etc. They eat young tender foliage preferring plants already damaged by a prior pest.
CONTROL: Natural‑remove garden rubbish which may harbour slaters. Chemical‑some types of snail bait are effective.
SLUG & SNAILS‑ These will attack any relatively tender plant parts especially young seedlings. They are more of a problem in moist and poorly drained sites.
CONTROL: Natural‑use repellent plants such as prostrate rosemary & wormwood. Place out a saucer of stale beer (they drink it and will drown in the saucer). Crush them using your foot or some other solid object. Chemical‑ Snail pallets or powder.
TERMITES - Often called white ants, they are not true ants, or always white. They create colonies in soil or wood, and can cause severe damage to timber. They like high humidity and temperatures between 20-24 degrees C.
CONTROL: This is difficult without using very poisonous chemicals or woods that are termite resistant, or by treating wood with preservatives (e.g. treated pine, creosote soaked timber).
THRIP ‑ These tiny insects swarm over leaves & flowers in hot summer. The usual symptom is flecking of leaves or flowers. Ficus, Hibiscus and other shrubs are susceptible to thrip attack.
CONTROL: Natural‑A small board painted white and covered with a sticky substance such as honey will attract and hold thrips. Chemical ‑ Malathion or Derris Dust.
WASP GALLS - Small wasps that lay their eggs in young plant tissue, which stimulates the plant to produce extra cells, which develop into galls. The larvae feed on the plant tissue, and when mature emerge through holes they make in the walls of the galls. These are common on Australian native plants, such as Eucalypts and Acacias.
CONTROL: Prune affected parts off the plant. Encourage new growth in the plant (e.g. fertilising, watering).
WEEVILS - Weevils are a type of beetle with a characteristic long snout. There are many different types and they attack a wide variety of plants.
CONTROL: as for Beetles.
WHITEFLY ‑ There are many different types of whitefly. The young six legged insects are minute in size, they feed on leaves and produce scales from which small winged flies emerge. They can occur in large numbers on many types of ornamental & crop plants including: eucalypts, potatoes, tomatoes, beans, many herbs, etc.
CONTROL: Natural‑use repellent plants such as nasturtium & marigold. Chemical‑Malathion, Pyrethrum.
WHITE WAX SCALE (see Scale)
FUNGAL DISEASES ON PLANTS
ALTERNARIA - There are different varieties of this disease, and they cause blights (parts of the plant stop growing and die, often without rotting), and leaf spots, sometimes both appear together.
CONTROL: Use Zineb or copper based fungicides.
ANTHRACNOSE ‑ Dark brown or black sunken spots on the stems, fruits or seeds. It is a common fungal disease on avocadoes, mangoes and beans.
CONTROL: Remove diseased plants & burn, use clean seed. Don't replant susceptible crops in affected areas.
Chemical - Mancozeb, Zineb, Copper sprays
AZALEA PETAL BLIGHT (see Petal Blights)
BLACK SPOT OF ROSES - A type of leaf spot related to anthracnose diseases (caused by the same pathogens). Leaves develop snmall to large, black circular spots. Areas around the spots can become paler. Badly affected leaves can become very yellow and drop.
CONTROL: Remove and burn affected leaves. Ensure good ventilation around the plants. Spray with Mancozeb or a triforine-based spray.
BROWN ROT ‑ Fruits go brown in patches. In advanced stages rings/stripes of yellowish mould appears. Mummified/infected fruit can fall to the ground and carry the disease through to the next season. A range of sub-tropical fruit trees are prone to this disease.
CONTROL: Natural‑Remove infected fruit & burn as soon as detected. Chemical‑ Zineb.
BOTRYTIS ‑ A grey mould that is a serious disease on flowers. It occurs in humid weather attacking a wide range of plants. Flowers become spotty at first, then later they rot and become covered with a fluffy mould. Badly diseased buds fail to open. Botrytis can also affect stems and leaves with mouldy rot and fluffy grey growth.
CONTROL: Natural‑Water underneath the plant directly onto the soil. In particular keep flowers dry. Any diseased flowers should be removed and burnt. Chemical‑ Fongarid, Chlorothalonii.
BRACKET FUNGUS – Symptoms include mushroom like growths ranging in colour from white to yellow to red. Can be an indication of more serious wood rot inside of plant/tree. If this occurs at tree base, and rot has progressed too far the tree must be removed and burnt. CONTROL: Chemical – Spraying with Fongarid gives some preventative control.
CINNAMON FUNGUS (see Phytophthora)
COLLAR ROT - Common on young seedlings and vegetables. Brown patches appear on the stem near soil level, The stem may be completely ringbarked. Some larger, established trees may also be affected (e.g. Citrus).
CONTROL: Dust seeds with a fungicide before planting. Ensure good drainage and ventilation. Use sterilized seed raising mixes. For citrus cut away any infected parts with a sharp knife and paint with a copper-based paste (e.g. Bordeaux, Kocide). Ensure mulch materials are not placed in contact with the trunks of citrus.
DAMPING OFF ‑ There are five main fungi species causing damping off (different types of either pythium or phytophthora). This disease occurs on young seedlings and is a serious nursery problem. The plant rots at the base and collapses.
CONTROL: Natural‑Cleanliness,hygiene & good drainage.Don't plant too close together.
Chemical‑ Zineb, Fongarid or LeSan DX. Other fungicides can be more effective on particular types of damping off (eg:Previcur kills pythium but not phytopthera).
DIE BACK (see also Phytophthora) ‑ Kills the tips of the plant,and continues killing the stems and leaves as the disease spreads throughout the plant. Leaves tend to look pale and wilted. There are different types of fungus diseases which can cause die back. The most serious type of die back is cinnamon fungus which can cause death of fully grown trees. Die back can also be caused by waterlogging.
CONTROL: Natural: Cut off infected parts & burn. Feed & water if infection is not bad.
Chemical: You must identify the type of die back and select the appropriate chemical. If unsure, try Fongarid.
DOWNY MILDEW ‑ Often occurs in damp conditions. The upper leaf surface goes yellow while a grey mould begins to develop underneath.
CONTROL: Natural – Practice garden hygiene such as removing damaged plant materials and providing good air circulation. Chemical: Zineb, Mancozeb, Fongarid, Copper sprays or Sulphur.
LEAF SPOTS - These are some of the most common diseases, caused by a variety of fungi and bacteria, including ones which cause other diseases (e.h. Alternaria, anthracnose). Thewy lead to spots or discoloured tissue (often brown or black) on leaves.
CONTROL: They generally only require attention when the outbreak is serious. They are most common after wet weather. Affected leaves can be removed, and a fungicide used,
Reducing humidity around infected plants can help minimise spreading of the disease.
POWDERY MILDEW - Causes a white powdery growth on the leaf surface.
CONTROL: Natural ‑Don't overcrowd plants, water from underneath in hot, humid or moist conditions. Chemical ‑Mancozeb, Lime sulphur, Triadimefon.
PEACH LEAF CURL - Causes large reddish blisters to appear on peach or nectarine leaves early in spring and throughout the season. The disease reduces tree vigour but does not normally kill. The fungus carries over winter in the bark and bud scales of the tree. New varieties of low-chill stone fruit are susceptible to this disease.
CONTROL: Chemical: Copper based sprays early in the season and repeat regularly through spring and summer.
PETAL BLIGHTS - Petals discolour and then rot, often resulting in a slimy brown mass, which in time dries out and becomes papery and brown. The petals remain connected to the plant. If humid weather continues black, seed-like bodies called sclerotia develop, which can cause infection in later seasons. Common on Rhododendron and Azaleas.
Control: Spray with Benomyl or Mancozeb- based sprays.
PHYTOPHTHORA CINNAMOMI - Commonly called cinnamon fungus (and sometimes dieback), this is a very serious disease that affects a wide variety of ornamental, fruiting and timber species. It is commonly associated with wet soils and heavy clay sites, with soils that have a low pH, or soils that are poorly drained or become waterlogged in wet seasons. Many germinating seeds and new seedlings in warm humid propagation structures (e.g. greenhouses) are very prone to attack from this disease.
CONTROL: Very few fungicides will control it, but furalaxyl based sprays (e.g. Fongarid) may give some control. Soils and potting mixes can be sterilised prior to planting or sowing seed. Improving drainage will often help. Do not import soil or plants from areas known tio be affected with this disease.
ROOT ROT - Causes leaves to turn yellow and rot from the tips.
CONTROL: Natural – Ensure the sight has good drainage. Chemical ‑Fongarid, Natural improve drainage.
RUST - This fungus causes browny orange spots or stripes, normally on leaves. Affects a wide range of plants including grasses, roses, beans, etc.
CONTROL: Natural – Maintain good garden hygiene by removing infected plant matter. Chemical ‑Mancozeb or Zineb
SOOTY MOULD - this is a secondary infection caused by the infestation of sap sucking insects such as scale and mealy bugs. The insects excrete a sugary substance which encourages the development of the fungus sooty mould. Symptoms include black sooty covering of the leaves and stem. This will make the plant unsightly, reduce the photosynthetic ability of its leaves and may reduce its overall vigour.
CONTROL: Control the insect! White oil is the usual treatment used.
VERTICILLIUM WILT - A disease that attacks many different plants. Symptoms vary according to the plant affected. Generally lower leaves change colour (e.g. become yellow or pinkisk-green to purple), then wilt and die. This progresses up the plant. This is a soil-borne disease, and spores may remain in the soil for years.
CONTROL: Rotate crops, improve drainage, and remove infected plants and bury them deeply or burn them.
Weeds are the one thing every gardener hates, but every gardener has; to a greater or lesser degree. If you want to reduce the maintenance requirements in your garden control weed problems thoroughly, and as soon as they are detected. If a weed problem is left, it just gets worse, and if you let weeds produce seeds, the problem can just blow out of all proportion. Some weeds can produce thousands of seeds, and that can mean by putting off pulling out one weed for a few weeks, you will end up having to eradicate thousands of its offspring a few months later. Be aware that some weeds can reproduce vegetatively as well as/instead of seeds, for example: Kikuyu grass, dock, dandelion, californian thistle. Thus removing the weed will not necessarily eradicate the problem.
You will never get rid of weeds completely from a garden, but the simplest way to deal with weed problems is to create a garden designed so that weed growth is discouraged, and the odd weed which does grow is not so noticeable.
HOW TO DISCOURAGE WEED GROWTH
*Use mulch mats
*Plant ground cover plants
*Install hard surface strips (e.g. concrete) beside or under fence lines to prevent weeds growing through.
*Feed lawns and garden shrubs so they can compete better with weeds.
*Apply irrigation by dripper so you don't water areas between plants and promote weed growth there.
*Apply fertilizer at the base of desired plants where it will be used by that plant rather than spreading widely between plants where it will encourage growth of weeds.
*Have solid fences or barriers surrounding your property to stop weed seeds being blown in.
*Avoid bringing in soil contaminated with weeds (including pot plants with weeds growing in them). Be careful with plants given to you by friends.
*Avoid garden plants which sucker or self seed and could become a weed.
HOW TO MAKE WEEDS NOT SO NOTICEABLE
*Have a more informal garden style...weeds don't look so much out of place.
*Plant a rich variety of different plant textures...then the weed will not stick out so much.
*Avoid highly manicured gardens with well defined lines (eg. edges to garden beds).
WAYS TO KILL/CONTROL WEEDS
Be sure to remove them before they seed!
Mow them regularly.
Cultivate them (e.g. use a hoe to uplift them from the soil). Do this on a hot sunny day which will effectively kill most annual weeds. Also, cultivate them into the ground. You may have to do this several times before planting your garden. Be careful with weeds that sprout out from small sections. Chopping up the parent plant and leaving the pieces in the garden can encourage the spread of that particular weed.
Pull them out by hand. They can be placed in the compost heap if it is hot thus killing any seeds and the plant itself. Remove seeds before placing weeds into the compost heap.
Graze (eg. goats/sheep/poultry...there may be legal restrictions in residential areas).
Burn them, using a weed burner - this is only generally effective at killing annual weeds.
Solarisation - clear plastic sheets spread over weed infested areas will create a high heat beneath the plastic killing the weeds, and encourage weed seed to germinate with young seedlings then being killed by the heat.
The use of chemicals is the most widely used method of weed control in the developed nations. If planning to use any chemicals there are several steps you should follow:
* READ the instructions carefully
* Spray on a windless day
* Wear clothes that cover the entire body
* Mix and use chemicals as directed
* Spray those weeds only specified by the label. In other words use the right chemical for the particular weed problem
* Thoroughly clean hands and remove and wash clothes after spraying.
* Be careful not to spray chemicals where bees are active.
There are all different types of chemical treatments which can be used to kill weeds. Some are permanent and have side affects which may not be desirable (eg. The ancient Romans applied salt to roads to kill weeds. Some of these roads 2000 years later still will not grow weeds...but today, they might not be a road any longer).
To use herbicides effectively, some knowledge of the chemicals used and their effect on plants and the soil is required. Herbicides are either selective or non-selective. They work by either contact with the plant directly, killing what it comes in contact with, or by translocation meaning that it may be taken up by part of a plant then moved to other parts. Some translocated herbicides also act by contact.
Selective herbicides affect only certain weeds. Generally they will eradicate broadleaf weeds without harming grasses or vice versa.
Non-selective herbicides will affect everything they come in contact with - both weeds and desirable plants. The degree to which they work will depend on the chemical used and the plants/weeds it is used on. Annual weeds may be killed with one application while weeds may require several applications.
A translocated (or systemic) herbicide's main advantage is that if you only spray a small portion of the plant, the chemical will be transported throughout thereby killing the entire plant, roots and all. Glysophate is translocated herbicides that does not stay active in the soil so is relatively safe to use. This is sold under trade names such as Roundup, Zero, & Weed Killer.
Contact herbicides are reasonably effective against annual weeds. To kill any weed, this chemical must come in contact with the plant.
Residual herbicides stay active in the ground for a period after the application. This is good in situations where a path is having problems with weeds appearing between the pavers. This chemical will prevent future weeds germinating for up to a one year, period, or even longer depending on the concentration of herbicide used. This however can be seen a problem for some gardeners. Care is required as to application and distribution around the garden.
Australian Correspondence Schools incorp. Australian Horticultural Correspondence School
Established in 1979 by well known garden author, editor, nurseryman, John Mason. The college offers 150 different garden and horticulture courses, for general interest, careers, professional or job development.