Environmental Problems for Plants

Heat, cold, wind, rain, frost, shade, pollution and other environmental problems can have disastrous effects on plants. Plant varieties vary in their tolerance of these conditions, for example the heat which might kill one plant may simply slow the growth of another.

Some plants may adapt to certain extreme conditions over time under normal circumstances, but when those same conditions occur suddenly, the same plant may be badly affected. Some plants, for example, will develop hard, cold tolerant foliage over autumn which will withstand the low temperatures of winter; but grow tender less hardy foliage in spring which will suffer if confronted with an abnormal period of cold in mid-spring.

FOLIAGE BURN

Foliage may be burnt by any one of a number of things.

a/ Water related

• With some plants, wet foliage is likely to burn in direct sunlight.
• Direct sunlight on African Violet leaves often causes burn marks.
• Conifers which are watered on the foliage on a hot day commonly develop burn marks later.
• Generally plants with soft or fine foliage are most susceptible to this type of burn.
• Think about when the burn appeared. Was it straight after a hot day, and was the foliage wet then?
• The symptoms would occur on the parts which were wet and most exposed to the sun (except in severe cases, burn would only be on one side).

b/ Sun Scorching

Shade cloth is a good way of protecting plants from severe affects of sunburn...If a plant is exposed and continually burning, then it is probably best moved or got rid of.

• Burn will be worse on the most tender growth (usually the young leaves or growth tips).
• It will be worse where the plant gets greatest exposure to the sun.
• Symptoms will show very quickly (by the next day).

c/ Pollutants

• Chemicals in the soil can cause a more generalized burn (ie. Growth tips or young foliage spread all over the plant show burn, unlike sun burn which might be on one side only).
• Consider whether the soil might have been polluted by a previous owner or if chemicals may have washed in from a neighbour's place.

d/ Pesticides

• Overuse of many types of insecticides or fungicides can burn foliage they are sprayed on.
• Spraying on a hot day can cause foliage burn.
• Look for the effect on the foliage most exposed to the chemicals.

e/ Fertilizer

• Too much fertilizer can burn root tips, and in extreme situations, cause burn marks on foliage.
• Fertilizer burn is more likely in hot weather when many fertilizers become more soluble due to the warmth.

Treating Foliage Burn:

• Damaged foliage cannot be repaired. It can only be removed to prevent decomposing tissue spreading infection to healthy tissue.
• Feed damaged plants, unless the burning is the result of over-feeding, and try to look after them well so as to promote rapid rejuvenation.
• Avoid making the same mistake again by not putting susceptible plant varieties where they could suffer the same fate.

POLLUTION

Pollution symptoms are generally burning or discoloration of leaves and growth tips.

The effects will be worse in badly polluted areas, so if you suspect pollution from a nearby factory, look at plants growing closer to the factory; they should show more dramatic signs of pollution.

The environment can be polluted in many different ways:

Gas Leaks: Plants growing near leaking gas mains or gas containers can be seriously affected. In cases of suspected gas leaks contact the relevant agency (ie. gas supplier) immediately.

Spillages: Spilling weedicide, beer, detergents or oil on the garden can burn roots and in severe cases kill foliage.

Air Conditioning: This can affect indoor plants. Air conditioning changes gas levels to the detriment of plant (and people) health. Some plants tolerate air conditioning better than others (eg. Phoenix roebellini is better than many other palms in such conditions). Plants which are rapidly growing react faster to the poor conditions of air conditioning, so reduce feeding and watering while plants are under air conditioning. Remove plants at least every 10-12 weeks and grow in a well ventilated but protected place to rejuvinate before returning to air conditioning.

LACK OF WATER

Insufficient water can cause foliage to wilt, or drop from a plant.

Fruit can sometimes also shrivel.

Treatment:

• Ensure adequate water is getting to the plant. This may mean you need to irrigate in some manner (e.g. sprinklers, drippers).
• Often when soil is over-dry, water is repelled by the soil; so even flooding the ground does not necessarily work.

Water must get to the roots. One of the following methods may be necessary if the problem is severe:

• Dig a trench around the roots, only deep enough to break through any impermeable layer, being careful not to disturb the roots, and fill with water. Allow the water to slowly soak in to the roots.
• Dig a deep hole beside the plant (perhaps with an auger) and keep filling with water, allowing the water to soak in deep.
• After watering, mulch with a moist, organic mulch to help retain water in the soil.
• Apply a wetting agent to help improve water penetration into the soil

DRAINAGE PROBLEMS

*Too much water around roots encourages fungal root rots, or causes the plant roots to suffocate from lack of oxygen.

*Young root tips are white when healthy, but black or brown when not.

*Leaves often go yellow demonstrating a nitrogen deficiency induced by too much water around the roots.

Treatment:

‑Lay drainage pipes.

• Use pots with a greater number of drainage holes.
• Aerate the soil with an aeration fork.
• Apply gypsum or lime to break up the clay particles in the soil.
• Add organic matter to soils to help improve the soil structure, and hence infiltration of water into and through the soil.
• On water repelling soils, such as some fine sands, apply a wetting agent to improve water infiltration into the soil.
• Plant susceptible plants on mounds or in raised beds.
• Slope the soil surface in your garen so that excess water runs away from areas where it may be a problem to areas where it won't be a problem, or to where it can be disposed of, such as into a storm water drain , creek, or natural drainage basin.

FROST

*Frost burn generally appears as dead areas of foliage, and stems.

• Affected parts turn black, and they may go watery.
• Symptoms begin to show within hours of the frost occurring.
• Areas on the outside of the plant are most affected. Leaves closer to a wall or other plants are less affected.
• It can affect leaves, growth tips, fruit, flowers and buds.
• Frost damage to fruit buds or flowers can cause a great reduction of fruit from crop trees.

Treatment:

‑Don't remove burnt foliage until the danger of further frosts has passed. Dead damaged tissue should be cut off to prevent infection spreading as soon as frosts finish. Premature pruning will stimulate new shoots which will be particularly tender and exposed to frost damage.

‑Cover with hessian or some other physical protection.

‑Create air movement to stop frost settling (eg. In a frost prone greenhouse, a cheap fan might be left on overnight when there is a frost warning).

‑Use a heat source (eg. a kerosene fire or fan heater) on frost warning nights. Even in the open, a small fire creates air movement which is often enough to prevent frost settling.

‑Put sprinklers on for a few hours just before dawn when the chance of frost is greatest. The slightly higher temperature of the water is often enough to prevent frost damage.

-Place plants under shade cloth or greenhouse film during frost prone periods.

-Use a temporary or permanent wall close to the base of the plant, and high enough to overshadow it. This wall must be twice the height of the plant and located within a distance of half the plant's height...or four times the height of the plant and located no more than a distance away which is equal to the height of the plant.

HAIL

• Hail can severely damage fruit, flowers and foliage.
• The damage is obvious, causing denting and tearing of plant tissue.
• Damaged tissue cannot be repaired and is normally cut off.

SHADE

*Areas of a garden can become increasingly shaded as trees grow, without you noticing the change.

*Growth can become elongated and less bushy as plants stretch toward the light.

*Plant vigor and flowering can become reduced.

*Soil dries out more slowly in shaded areas. Algae or moss may grow on paths or lawns.

Treatment:

‑Remove some of the large trees.

‑Thin out branches in the tree canopies of large trees to let more light penetrate.

‑Replace some of the evergreen trees with deciduous trees to let more light in over winter.

‑Replant under trees with plants more suited to shade (eg. Dichondra as a lawn, Hosta lilies, clivia, impatiens, ferns).

TEMPERATURE

a/ Cold

*Cold temperatures slow down growth and reduce flowering and fruit development if not extreme.

*Extreme cold will kill parts or all of a plant very quickly.

b/ Heat

*The first symptom is slow growth, or no growth.

*As heat increases, the plant will wilt.

*In extreme heat parts or all of the plant will die quickly.

Treatment:

‑Mulching generally reduces temperature in hot weather, and increases temperature in cold.

-Improving ventilation can also modify temperature extremes (eg. prune or remove structures such as sheds or fences) to allow more air movement through the garden).

‑Watering and shading can reduce temperature extremes.

-Cover stone, concrete, ceramic, brick, metal, glass and other such surfaces which heat up easily and radiate or reflect heat. Do this by increasing shade (eg. building a pergola, planting shade trees etc), or by growing hardy vegetation (eg. climbers or tub plants) over such surfaces.

WIND

*Strong wind causes foliage to dry out faster than water can be taken up from the roots. This causes wilting, particularly with more susceptible newly‑planted plants.

*Damage will be worse on the more exposed side of the plant.

*Damage will be worse on growth tips and most tender foliage.

*strong winds can also cause physical damage, causing branches to snap, or leaves to be blown off. This can reduce the vigour of the plant (less leaves to produce food), and open it up to attack from pests and diseases (e.g. uneven/broken branch stubs, or split trunks).

*Plants can literally blow over, in extreme cases, out of the ground.

Treatment:

‑Erect or plant a windbreak.

‑Use tree guards until the plant becomes established.

‑Stake plants to stop them blowing over.

PLANTS HAVE VARYING TOLERANCE LEVELS

Every type of plant has a different level of tolerance to adverse environmental effects:

*There are certain environmental conditions which are preferred (eg. Most plants prefer a temperature between 22 and 30 degrees celsius, a soil which is neither waterlogged or bone dry and plenty of light but not that much that it burns the foliage. Plants generally grow best within such a range).

*There is a broader range of environmental conditions which are tolerated (eg. Most indoor plants will tolerate temperatures down to 5 or 10 and up to 40 or 45 degrees celsius; but below 15 or above 35 there is little if any growth).

*Outside of the tolerated range of environmental conditions the plant will suffer and perhaps die. Many tender indoor plants will die at temperatures below 5 or above 45 degrees celsius, others tolerate temperatures below zero.

Wind, frost, pollution and all other environmental conditions affect all plants in the same way as the examples above; in otherwords they have preferred, tolerated and intolerable environmental conditions for growth.

This is where good plant selection plays an important role. By choosing plants that tolerate or prefer the growing conditions that you have, you will greatly reduce the likelihood of plant problems occuring. Alternatively, if you wish to grow other plants, that may not grow readily in your area for some reason, then you need to modify the growing conditions in some way to better suit those plants.