Gardens are constantly changing. Small plants develop into mature trees with falling leaves and sometimes, seemingly inexplicably, a tree which may have been a good friend for many years suddenly dies.
In nature there is a purpose and use for everything, even for fallen leaves, but in the garden things can seldom be entirely natural. The gardener may have inadvertently caused a tree to die or may need to remove some leaf litter if it becomes too much.
Why your favourite indigenous plant is dying
The demise of a plant is often blamed, incorrectly, on insects. Although some may succumb to attack by foreign pests, local plants are unlikely to be destroyed by indigenous insects.
Even trees that have been totally defoliated soon sprout again. The termites sometimes found in a dead tree are not usually the cause of its death.
The most obvious reason could be that you may literally be “barking up the wrong tree” by having planted something unsuitable, which doesn’t belong in your area in the first place.
Another possibility is that your tree has a limited lifespan because it belongs to the group referred to as pioneer trees. Good examples are Trema orientalis (Pigeonwood) and Albizia adianthifolia (Flatcrown).
These grow unusually fast and, in so doing, provide protection for slower-growing species. After the slower plants have caught up, the pioneer dies out while its offspring are coming up elsewhere, for example, in grassland or some disturbed area.
This is how forests are formed.
Pioneers usually start to grow in an area where trees have been destroyed and, outside their natural areas, they often become invasive. As a rule of thumb, the faster the growth rate of a pioneer species, the shorter its lifespan.
If you have a large specimen of a pioneer tree in the garden, it is a good idea to plant a younger one close by to replace it when its life is over, although, if you look around, you may well find that offspring are already coming up naturally nearby.
It is possible for tree roots to be damaged during building operations. In addition, the builder may have buried waste material on the site which could become toxic to the trees.
Sometimes when the forest undergrowth is removed for a building site the large trees left standing slowly die, to the surprise and disappointment of the concerned owners.
It seems hard to believe, since the rainfall in the area has not changed, that the trouble is probably due to drought.
The explanation is that on windy days there is little movement of air inside a forest. Wind entry is limited as the verges are usually made up of thicket, often almost smothered with creepers, and the branches and leaves on top form an unbroken canopy. Thus transpiration is mostly from the outer layer of leaves. The ground, which is covered with a thick layer of dropped leaves, is not exposed to the sun and remains cool and moist.
These are idyllic conditions as far as forest trees are concerned. Now isolate one of these big trees. Its large leaf surface is exposed on all sides, and even a slight breeze causes a high transpiration rate.
The mulch cover is replaced by lawn and the ground becomes dry and hot.
Although the grass may be watered to a shallow depth, it does not take long for the soil below to become dry and the tree suffers as a result.
So to keep it alive it needs thorough watering, not just around the trunk, but at least as far as the outside edge of the tree.
Very often a large tree is saved for the shade it provides and the area around it gets paved or tarred. The rainwater, which the tree received before, now all runs off into a drain. It is, therefore, advisable to leave some holes where surface water can seep into the ground. Trees with large taproots are less dependent on surface water.
Like humans, some trees live longer than others of the same species.
While people have used their scientific advances to protect and thus prolong the life of weaker individuals, in nature it is always the weaker plants and animals which die first.
A weaker plant will be the first to be attacked by insects, and also the most likely to succumb to drought which has less effect on most other plants of the same species.
You may sometimes observe this in the bush when, after a period of drought, you find some dead plants among surviving members of the same species.
Unfortunately, you will not know whether the plant you buy is genetically weak or strong, and most gardeners wish to retain their specimen even if nature feels it should be eliminated. Therefore, it may be advisable to water any plants showing signs of stress during periods of severe drought. As they get older and larger, many trees, despite being quite healthy and unlikely to succumb themselves, have branches that die off.
Unless these are a potential danger, there is no reason other than cosmetic to remove them. Not only can they provide nest sites for some birds, but the decaying wood will attract caterpillars and other insects on which tits, wood-hoopoes and woodpeckers feed. No wonder the genus name for the Golden-tailed Woodpecker is Campethera, meaning caterpillar hunting.
The bark of many indigenous tree species is used for remedies by traditional healers. In addition other parts of certain plants, such as the roots, leaves, fruits or stems, may also be used. The reduction in availability of indigenous plants, and the concurrent growth in population, means that the pressure on these resources is increasing at an alarming rate.
Wise and knowledgeable herbalists remove only small amounts of bark and leave the tree long enough for it to heal before re-use, thus ensuring a sustainable resource for the future. This will usually not harm your tree and it is unnecessary to take preventative action.
Unfortunately there are also some unscrupulous middlemen who will quickly seize the opportunity to make a fast buck by selling bark to traditional healers. Without regard for the tree, they often rip off large amounts, causing the demise of the plant. To protect your trees, paint the trunk with any ordinary household PVA. This will not harm the tree, but the bark will be considered contaminated and its value will thus be much reduced on the traditional medicine market. Any colour can be used, but brown is most likely to blend in with the surroundings. Some of the trees, which are often debarked in this way, include Albizia adianthifolia (Flatcrown), Bridelia micrantha (Mitzeeri Sweetberry), Harpephyllum caffrum (Wild-plum) and Sclerocarya birrea (Marula).
Make the mostof garden waste
Robin-chats and thrushes find food among the decaying leaves beneath sheltering vegetation. If your garden is pristine clean and raked bare, these species will stay away.
It is not necessary to dig the soil over, especially around plants. In fact, this damages the surface roots and weakens the plant. Rather allow leaves to remain where they fall under shrubs and trees and even add those raked from lawns and paths. Much is often written in garden columns discouraging this, because it will supposedly harbour pests.
Perhaps retaining fallen leaves may not be to the advantage of some temperamental foreign plants, but the answer is to look at nature where leaves never get raked up.
As in the bush, bare earth should never be visible in your garden. Even grass cuttings can be added, but they must be mixed with leaves or other organic material as, on their own, they will form a dense mat, slowing down the decaying process and reducing the nitrogen content of the soil. Not only will this decomposing material attract insects and birds, but it will also form valuable natural mulch, retaining moisture and eventually turning into compost, which will enrich the soil. Nature will do all this for you.
It may not be practical to deal with all garden waste in this way, because if the mulching layer becomes too thick it can stifle germination of new plants. Although this would help deter unwanted aliens, it could also prevent exciting indigenous seeds, brought by wind or wildlife, from coming up. Therefore, especially if you do a lot of trimming, it is usually necessary to establish a compost heap for biodegradable material. This is far better than leaving it in plastic bags on the pavement for disposal.
Much of your kitchen waste, like vegetable peels, apple cores, coffee grounds and even tea bags can be included in the compost, while egg shells should preferably be crushed to promote speedy rotting. Avoid any non-biodegradable matter such as plastic, glass and cellophane. Tinfoil and metallic wrappings are extremely slow to disintegrate. Wood ash from the braai can be added, but avoid coal ash and any greasy or oily substances. For trimmed branches, the more finely cut up, the better. Thick wood will disintegrate very slowly and is best left to rot in the garden.
Commercially available plastic compost makers may be neat and tidy, but an open heap is the system that will attract the birds. Robin-chats will forage until they are by pushed out the more robust Hadeda Ibises, which extract the thick white larvae of the fruit beetles.
Flycatchers will dart in and out from their perches on the nearest tree to scoop up any disturbed flying insects. If you don’t fancy an informal, untidy pile, build a simple structure, about chest-high, from bricks or other materials such as treated poles and metal sheeting.
Leave a gap down one side through which mature compost at the bottom can be reached. The structure should have no floor, as the compost must be on the ground to allow earthworms access. There is no need to bring in additional earthworms which are available commercially. To prevent it drying out too much, the compost heap should ideally be positioned out of direct sun.
When starting a new heap it is best to put rougher material, such as twigs, in first. Air circulation is essential, so don’t compact the heap too much by, for example, stepping on it. Artificial compost activators will speed up rotting, but are not desirable if a nature-friendly process is preferred.
Compost is a natural fertiliser that is made all the time in forests, without activators.
If you are really impatient, and must have an activator, it is best to use manure or already-matured, good, rich compost for this purpose. To prevent the compost being “pirated”, it is wise to clear it out occasionally and sever intruding roots of nearby trees, which will have been heading straight for the nutritious heap. When starting again, the material that has not yet totally decomposed can be returned.
Most gardeners recommend turning compost regularly to accelerate the decaying process. However, this is not essential and, if not done carefully, may disturb or even harm little creatures living there, such as toads attracted to the rich insect life. At regular intervals, it is advisable to sprinkle a layer of soil over the compost and to water it. It should be kept moist but not wet, as beneficial organisms cannot survive in soggy conditions.
If done correctly, the compost will never give off a bad odour.
A good pile will generate enough heat during decomposition to destroy most weed seeds, and the resulting compost is useful as a potting soil, top dressing for lawns or a general soil improver.
Some garden plants become like addicts waiting for their next fix of artificial fertiliser. Homemade compost is the healthy, wholesome alternative.
l Bring Nature Back to Your Garden can be found at all leading bookshops, and can also be ordered for R165 from the Flora & Fauna Publications Trust at http://www.floratrustkzn.com. - The Mercury