Example of a lesson from our Arboriculture I course
Enrol in a Course to learn more about Plant Selection
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The success of a garden is largely determined by three interconnected factors:
The suitability of selected plants to the conditions in which they are expected to grow.
The use of optimum plant establishment techniques.
The garden maintenance regime.
A well-selected plant is more likely to survive establishment and be easily maintained.
WHAT TO PLANT WHERE
The first thing to consider with plant selection is the conditions where the plant is expected to grow.Environmental factors that influence the selection of plants include:
Climate – plants that originate from the same or a similar climate will be suited to the conditions.Extreme conditions such as snow and drought will prevent some plants from being grown in a given area.
Latitude – the closer to the equator means that temperatures are likely to be hotter and day lengths will be more even (variation in day length triggers flowering in some plant species).
Altitude – areas at higher altitudes generally experience cooler temperatures.
Oceans and lakes – large bodies of water alter growing conditions by moderating temperatures.
Soil – soil type, drainage and nutrition.
Winds – strength and direction.
Microclimate – factors that influence growing conditions in a specific area such as shade from large trees, reflected heat from hard surfaces and buildings, protection from winds by fences
Water – rainfall and irrigation.
Pests and diseases
Human activities – pedestrians walking on turf, children playing ball games, vehicles, etc.
There are many reasons why plants do not grow well in a particular garden or in a particular place.Most of these are caused by a combination of local climate and soil conditions.Some common problems include:
Alkaline soils – these are soils with a pH greater than 7.
Waterlogged soils – where drainage is poor, generally due to the site being in a low lying area, or because of poorly structured soils, such as heavy clays.
Salinity – in some parts of the world, this is a problem not just in agricultural areas, but increasingly in urban fringe areas.
Strong winds, poor soils and salty conditions associated with coastal areas.
Hot, dry areas.
There are two main ways to overcome such problem areas in the garden.
Modify local conditions to better suit the plants you wish to grow, such as providing irrigation in hot, dry areas; or growing or building a windbreak in windy areas, improving drainage, or lowering soil pH in alkaline soils.Such remedies can often be very difficult to achieve, time consuming, or expensive.
Grow plants which suit, or will cope with the conditions present in the garden. If you choose your plants carefully you can often have a garden that is very rewarding in terms of its appearance, and its hardiness.
SELECTED TREE SURGERY TECHNIQUES
This procedure can be compared with cavity work dentists carry out on teeth. Trees, like teeth, can develop rot in their tissue. Cavity treatment basically involves removal of rotten wood and filling the cavity with some solid material. In the past, concrete was a popular cavity filler; urethane foams which are flexible, non-toxic and water resistant, are now recommended.
Cavities can start from neglected bark injuries, from a stub left after a branch has fallen or been removed etc. Small wounds in most healthy trees will compartmentalise and should not need cavity treatment. When cavities do develop, any treatment should aim to minimise interference with this natural process. In the past, holes were often drilled into the cavity to drain water, but this is now rarely done as it is likely to damage the compartment walls and promote decay spread.
Often cavities will not need filling. Loose and decayed wood can be simply cleaned out of the hole; do not use a chisel to gouge out decayed wood. The tree may then be able to compartmentalise the decay. If this is not the case, a partial or complete fill can be used to encourage wound closure, prevent further damage or improve the tree’s appearance.
Cavity treatment will not improve overall tree vigour, health, stability or strength. Tree vigour can be improved by cultural practices such as adequate watering, feeding and soil treatment – these will help affected trees to combat further fungal attack.
Bracing and Cabling
These techniques are aimed at holding branches together which are otherwise in danger of breaking and falling. Bracing basically involves bolting metal rods into position between two branches. This holds the branches from splitting apart. Cabling involves tying the branches together using a metal cable attached to eye bolts which have been placed through the branches.
Bracing is primarily a preventative measure, ideally carried out before the tree begins to fracture. A mature tree with a splitting branch cannot be saved by bracing; the tree should be removed immediately as it poses a major safety risk. Young trees that show signs of obvious structural problems should also be removed, as they are not likely to be worth the effort and expense involved in bracing.
Cable bracing is the most common form of bracing. A flexible wire rope is placed between the trunk and branch to prevent excessive movement. If more than one cable is required on a leader, they should be placed at least 30 cm apart. Only one cable should be secured to a point of attachment.
Cable supporting co-dominant stems (ie. forked leaders) should be positioned about 2/3 of their length from their fork.
A cable attached to a trunk, supporting a heavy horizontal limb should be attached about 2/3 of the limb’s length at an angle of 45° to the limb.
Propping, like cabling or bracing, is an operation carried out to prevent damage. It involves placing a wooden or metal prop between a low, horizontal branch and the ground to prevent the branch sagging and breaking. Props can be made from steel or durable timber. The base of the prop should be placed on a firm pad, such as concrete, to prevent the prop and branch sinking into the ground.
TREES IN THE GARDEN
Before attempting your plant collection or tree reports for this lesson, read all of the following notes.
All too often trees are the forgotten giants of our garden areas. A shrub or ground cover plant is far closer to the human eye than a tree, and these plants usually get most of our attention because they are so easily seen. With trees it often seems to be "out of sight, out of mind".
Trees are in fact potentially far greater problems than shrubs. If a shrub blows over, it creates a bit of a mess and a gap in the garden bed. If a tree blows over, it can destroy half the garden, make a large hole in the roof of a house, or crush your new car. Trees, like people, can be hurt, they can get sick, and sooner or later they will die. They need to be fed and watered, and they do need "doctoring" if their life is to be extended to the fullest. Some trees, like some people, are hardier and never seem to become ill. In the same way, however, many trees have "medical" problems which no one seems to notice until it is too late!
The only real way to avoid a catastrophe with a tree is to closely monitor the plant. It should probably be checked (on average) once every six to twelve months. If any problems are found, they should be treated immediately.
Increasingly, tree care is recognised as an advanced science. We now understand the importance of regular attention being given to trees and, in studying this subject, you have a responsibility to monitor the trees you are seeing and let people know of their condition.
Start at the Beginning
One of the biggest problems with trees in gardens is planting in the wrong position. Some examples of this are as follows:
People are misinformed of the spread and height of a tree when they plant it. They might plant small seedlings under power lines which then grow into 20 m trees. At best, the tree becomes an eyesore when the electricity company cuts (or more usually ‘hacks’) away the offending branches. At worst, the tree is a significant safety problem, potentially bringing down live electricity wires during storms. Another common problem is when property owners plant very tall trees up against the wall of the house and branches rub on the roof, dislodging tiles etc.
Trees which cause damage to drainage or sewer pipes are planted too close to the pipes. The pipes then become blocked and either the tree has to be removed or regular expense is incurred as the pipes are cleaned out.
Trees which have damaging root systems are planted too close to paving or building foundations. Walls can be lifted and cracked, paths or driveways destroyed.
Often a tree which is expected to grow to 6m is planted in the front of a window for shade. When it reaches 20m, the room it is shading has become so dark that a light must be turned on, even on bright sunny days.
We all want the best value when we buy a tree but there often the cheapest plants are not the best ones to choose. What is the value in buying an inexpensive tree if it doesn’t live, or grows slower than a more expensive plant?
There are two decisions to make:
1. What plant variety you should choose.
2. Which plant from those available you should choose.
Some plants are very easy to grow; others are a great deal more difficult. Choose plant varieties according to your own capabilities and the amount of time and effort you are able to devote to caring for the plant.
If you don’t have the time to water, feed or otherwise tend to the tree after planting, it is better to choose varieties that do not require such aftercare.
If you don’t have the expertise to identify and spray pests and diseases when they come along, choose plants that are resistant to such problems.
If you have limited water available and live in a dry climate, you might be better growing drought-tolerant rees, rather than struggling with water-loving plants.
Even professional arborists often try to grow the plants they dream about, and end up with a collection of sick or slow-growing trees. These same people could have had a collection of healthy but different plants, if their choice of plants was better matched with their ability to care for them.
Be prepared to Replace Sick Plants
All plants have a limited lifespan – and that time varies from place to place.
Some trees (eg. Atlantic beech) may last for thousands of years; most last for hundred, but some may only last a couple of decades.
Some may be long-lived and resistant to pest or disease in one locality, but in another country or region could be highly susceptible and likely to have a shorter life span. For example, English elms in Europe are prone to Dutch Elm Disease but in Australia the same genus of elm trees is resistant to the disease, even though the beetle that carries the disease does exist in Australia.
At the nursery, you’ll be confronted with lots of choices, even after you’ve decided on the type of plant you want. Large, small, covered with flowers or not, bushy, or thin and tall – what’s going to give you the best results?
Plants that are healthier and not pot bound are more likely to grow faster and overcome the effects of disease or insect attack.
Larger plants may (according to species) take more effort to get established, but if you are prepared to put the effort in, will give a more immediate effect. If you don’t put the effort in, they are more likely to die.
Plants with a good, uniform shape, ie. straight stem, uniform branches and a good coverage of leaves, will get off to a good start as soon as they’re planted out.
Trees with several leaders (growing tips) may need side shoots removed or left (depending on variety) to encourage the proper development of a healthy crown.
Watch out for plants with lots of soft, lush new growth – these aren’t necessarily the healthiest or best plants to buy. Unless you can give the plant ideal conditions (moist, fertile soil in a sheltered position) lush growth is likely to wilt and die back once the plant is put in the ground. The plant will most likely recover but it may take several weeks for new shoots to grow.
A plant covered with flowers is appealing, but isn’t necessarily in good health. Even very sick plants can flower well. Instead, look for sturdy well-formed plants with healthy green leaves. If you really want a plant that will give you flowers quickly, choose one with lots of buds rather than fully opened flowers.
Check that your plants have not been exposed to a fluctuating water supply that will cause problems later on.
Try and ascertain whether the plants have been fed, and if so on what. A change in their nutrient supply can be devastating.
If the plants have been stored in a shade house, behind a windbreak, or in a greenhouse, they may need acclimatising. A tree guard may be essential, and for large plants that may be difficult or expensive to provide.
Avoid plants with any sign of insect attack or visible disease. Not only are these plants potentially going to die, but they could devastate the rest of the garden by spreading pests and diseases.
Observe the standards set around the nursery you purchase trees from. A clean and tidy site where health concerns are readily observed, is more likely to produce healthy plants than one where cuttings are left lying around, compost is left exposed and pots are not sterilised before re-use.
Don’t Be Afraid to Ask For Advice
A reputable nursery will give you sound advice on what are the best value plants for the garden. They won’t try to pressure you into buying their most expensive plants, nor will they flog off old, tired stock; after all, they need your repeat business.
Give the sales staff a clear indication of what you want – in terms of plant size, type and maintenance requirements – and you’ll be more likely to get the right plants for your garden.
HOW TO PLANT A TREE
Planting a tree might seem to be simply a matter of digging a hole and ‘bunging in’ a plant, but many trees fail due to poor planting techniques. If you follow these guidelines, your tree will have its best chance to grow to its full potential.
Select a site where there is ample room for the tree to grow to its full size. Do not plant close to buildings, under power lines, or over gas and water pipes.
Excavate the planting hole. The hole should be the same depth and approximately twice as wide as the container.
Avoid creating smooth sides to the planting hole. Roots will be unable to penetrate into the surrounding soil.
Remove the plant from its pot. Uncurl any circling roots, and if necessary, give the roots a light prune.
Plant the tree so that the soil level matches the level of the surrounding soil.
Backfill the hole with the excavated soil. If the soil is particularly poor, mix in an organic fertiliser before backfilling.
Gently firm the soil around the plant. Do not heavily press the soil down with your feet. This - will compact the soil, preventing roots from penetrating.
Water in thoroughly.
How to Water a Newly-Planted Tree
Remove the fitting from the end of your garden hose.
Insert the bare pipe into the disturbed soil around the new plant.
Turn on the tap to a gentle pressure. The planting hole will act as a sump, filling with water.
When water appears at the surface, turn off the tap.