Gardening Tips: A guide to pruning
Pruning is a subject which can confuse amateur fruit-growers, especially when they first start. In fact, pruning is not really difficult once you understand how the tree or bush concerned grows, and once you have a clear idea of what your aims are. There are full details of pruning requirements for all the major fruits in the individual Step-by-Step Guides.
In trying to meet the individual needs of particular fruits you can first divide them into one of several broad classes, depending on the age of the wood on which the fruit is produced. Assessment of site,, age and general health are also important, and for these you must depend on your own observations. The nurseryman who supplied you with the tree should tell you what rootstock it is on and will give information on its likely effect in terms of how vigorous growth should be.
The reasons for pruning
Pruning actually delays fruiting; if you leave a tree unpruned, it will begin to bear fruit much sooner. But despite this early start, the unpruned tree soon begins to suffer from neglect. The branches are thin and weak, they tend to break under the weight of their crop, growth becomes dense so that sunshine cannot penetrate and fruit colour suffers. Fruit size, too, is poor and often a habit of biennial bearing sets in, a reasonable crop one year being succeeded by a small one or even none the next. Branches grow in the wrong direction and, crossing one another, they may chafe so much that the bark suffers wounding, and disease is given a chance to enter. Obviously some control of growth is essential for the regular production of good crops of high-quality fruit.
The degree of control will depend on the system of training you have decided to adopt. Espaliers, fans, cordon bushes and pyramids all have slightly different pruning requirements. Early pruning should be directed to laying the appropriate framework of branches for one of these systems of culture but, once the initial shaping has been achieved, pruning is necessary to maintain that shape.
Other reasons for pruning are the need to cut out wood which is worn-out— after only one year’s fruit-bearing in the case of fruits in the one-year-old wood only class—and encourage the development of new replacement branches. Misplaced growths must be removed, cutting back branches which cross others, or redirecting branches pointing in an undesirable direction. You need to avoid crowding and too-dense growth which will shade the fruits unduly, but always remember that there is a certain balance to be maintained between the number of fruit and leaves; it is the leaves which, under the energising action of sunlight, turn the tree’s nutriment into further growth or fruit. Pruning may also be necessary to cope with pest, disease, storm or accidental damage, or as preventive surgery to prevent disease infection from entering.
Basic pruning principles
Understanding something of how a fruit tree or bush grows is a vital help in pruning. If you examine a branch or long shoot of a fruit tree closely in winter, you will see that at intervals along it there are tiny buds. Some of these are fatter than the others and more rounded. These are the blossom buds which will provide you with fruit. The others are growth buds, at present dormant. Some of these growth buds will start to grow in spring, producing leaves and shoots, others will eventually change into blossom buds and some will remain dormant.
Left to its own devices the branch of a young tree will grow longer and longer, season by season. Most of the buds, probably all, along that branch will continue in their state of dormancy. This is because the bud at the tip manufactures a growth-inhibiting hormone which it sends back down the branch.
If you prune that branch and cut away the tip, you remove the source of the growth-inhibiting hormone, at least temporarily. The result of this is that the topmost bud remaining will now grow out strongly, and several buds below will also grow with gradually diminishing vigour. Thus, where there was originally one branch or shoot, now we have two, three or perhaps four. In this way new branches and sub-branches are made and the framework of a young tree is built up.
Controlling bud growth
On quite a young tree, one or two years old, you will find that the topmost bud will tend to produce a vertical or near-vertical shoot. Buds below will produce shoots out at an angle. This is an important point to consider. For a pyramid or an espalier which is to have another tier of branches formed you want the central stem to go on upwards, but for a bush-shaped tree this is totally unsuitable. In the bush tree we want the branches to spread out so as to keep the centre open and uncongested. The aim is to have a bush with wide-angled crotches (the junction of primary branches with the trunk). Rather surprisingly it has been found that a wide-angled crotch is always stronger, and the branch able to bear a heavier load without breaking, than the narrow-angled.
If you are going to control growth you must be able to stop some buds growing altogether, selecting only those you want to grow, discouraging some which might prove too vigorous and encouraging others which might otherwise remain dormant.
To prevent an unwanted bud from growing is easy: you simply rub it off with your thumb. To stimulate a bud to grow, take a sharp knife and cut a tiny moon-shaped sliver of bark from immediately above it. The cut should be close to the bud, but not near enough to harm it, and deep enough to remove the layer just behind the outer skin of bark. This is called notching. Less often it is desirable to restrain the vigour of new growth from a bud and you can achieve this by cutting a little half-moon from the bark immediately beneath the bud. In this case the process is called nicking. Both nicking and notching are ways of restraining the sap flow in one direction or the other.