Training Young Trees and Shrubs
Most trees and shrubs grown in a garden are purchased from a nursery. It is useful for the gardener to know how these were raised, for it does have some bearing on.
Woody plants may be on their own roots, having been raised from seed, cuttings or layers; or they may have root system (rootstock) of one plant, and the above-ground part (scion) of another as a result of grafting. Trees may be grafted low, with their union (the point where the rootstock and scion are attached) close to the ground, or they may be high-grafted on to stems of varying lengths.
Remember that grafted trees and shrubs are likely to produce suckers from their rootstocks, and these, if left, grow away at the expense of the more desirable scion variety. Suckers should be removed by pulling as soon as they appear. Do not cut them off at ground level otherwise all buds below will start into growth, and where there was one sucker, there may soon be several. Scrape away theuntil the point of origin is exposed, then with a sharp downward pull remove the sucker; this takes away the basal buds which cutting would have left.
Trees are trained in two main ways: as standards which have a clear 1.8 m (6 ft) of stem, on top of which the framework is allowed to develop, and as central leaders, where the leading shoot is continuous with branches arising all the way along the length of the trunk (Fig 1). Standards are the form most commonly offered for sale by nurseries and are well suited to small-growing trees such as mains (flowering crab apples) and sorbus (mountain ash). But for the larger-growing trees, such as betula (birch) and quercus (oak), the central leader should be tied.
After planting, select and retain three or five of the strongest shoots, cutting back sideshoots to two or three buds, and reducing their length by about half. This should encourage new shoots to develop near to ground level during the following growing season; in the next winter these main stems are cut back again to half their new growth. At the same time the centre of the bush should be opened up by removing crossing branches and any clutter of short shoots. Cut back the remaining sideshoot to two or three buds, and thin out the branches where there is crowding, so as to produce a well-balanced, evenly spaced framework.
These are planted in spring to the same depth as they were in the nursery, having first been given a good soaking. Select the three strongest shoots, reducing the remainder, and lightly tip or remove their growing points. In the following spring, thin out crowded branches and open up the centre of the bush.