Growing Trees for Size and Shape
Height No Limit
Trees are the largest plants in the garden, the most permanent and the most dominating. Well chosen and placed, they can give it character and provide striking focal points. Badly chosen or overcrowded, they can become oppressive and make it difficult for other plants to grow.
Intrees must nearly always be used as single specimens or in very small groups. In larger gardens it may be possible to use them to form coppices or woodlands, but if you decide to underplant with shade-loving shrubs, such as and , the trees must be fairly widely spaced so that the shade is not too dense and the not too impoverished by their roots. Dappled shade is the ideal to aim for, with sunshine filtering through the canopy of leaves.
Trees vary enormously not only in their ultimate size, which may be anything from 4-40m (13-130ft) under British conditions, but also in habit. They can also be deciduous or evergreen and many of the evergreens belong to the great conifer family characterized by narrow, often needle-like leaves, for which reason a distinction is often made between broad-leaved trees and conifers. Trees also vary greatly in shape and branch pattern. Most native British trees are deciduous and rather billowy in outline. By contrast most conifers are evergreen and conical, creating a rather spiky effect very different from that of the oaks, beeches, elms and limes.
Some trees spread their branches widely and some hold them erect, and there are also erect varieties of normally spreading trees. These are known as fastigiate. One form of the common oak makes a splendid upstanding specimen only 4-5m (13-16ft) wide, even when old, and there are similar erect forms of the black poplar, the common beech, the hornbeam, the tulip tree (liriodendron), the maidenhair tree (ginko), some of the ornamental cherries and many more. There are also fastigiate conifers, including several cypresses and junipers. Such trees give you height in the garden without corresponding spread. Even so, some spread their roots widely and limit what you can plant nearby. Elms and poplars are notable offenders; elms also produce suckers freely, often far removed from the parent tree, and these can be a great nuisance.
As well as rounded, spiky and columnar trees there are some with a graceful weeping habit. Popular weepers include the weeping ash, beech, birch, elm and willow.
Some trees are grown primarily for their flowers and some have yellow, copper, purple or variegated leaves which can also be usefully employed to enrich and extend the colour combinations in the garden. Some also have attractively coloured bark: notable among these are the numerous birches which have white bark; Acer griseum, in which the bark is cinnamon-coloured and peeling; the snake-bark maples, in which it is green striped with white, and Prunus serrula, in which the bark is a shining mahogany-red.
PLANTING AND CARING
Installing a new tree has become more flexible now that you can buy them — and shrubs as well — in containers from which they can be planted at almost any time of the year. The traditional method — lifting them from the open ground — can only be done with safety when they are dormant, or nearly so, between mid-October and late March. There is still much to be said for this way of planting, especially with large-rooting trees which do not fit easily into containers, however large. `Open-ground’ plants are also available in greater variety and often in larger sizes, and provided they are carefully handled and replanted quickly before their roots become dry, they often establish themselves more rapidly and satisfactorily than container-grown plants. If there has to be an interval between acquiring and planting your new tree, heel it in temporarily in a suitable hole in moist ground.
For planting in the final site, dig a hole with plenty of width to spare. Usually the soil mark on the trunk will indicate the depth at which the tree was growing in the nursery, and you should also allow for this when preparing the site. If no soil mark is visible, the uppermost roots should be covered with 5-8cm (2-3in) of soil.
Ground for trees should be well prepared by digging. Remove alland enrich the soil with manure or , plus a sprinkling of slow-acting fertilizer such as bonemeal. It helps to prepare a planting mix of garden soil plus half its bulk of peat or leafmould, a similar quantity of sand and a peppering of bonemeal. Work two or three spadefuls of this around the roots of each tree before the soil removed from the hole is returned.
Trees almost always require secure staking for the first few years and, to prevent injury to the roots, the stakes are best driven in before the trees are planted. This has the added advantage that the tree can be immediately secured to the stake, leaving your hands free to shovel in the soil which should then be trodden down firmly around and over the roots.
Little pruning should be necessary for a few years except to remove young stems from the main trunks if these are to be kept bare, and to thin out branches a little if too much growth threatens to spoil the natural shape of the tree. Later on, as trees become mature and some branches die or become injured, pruning should always be done in such a way as to preserve, so far as possible, the distinctive shape and branch pattern of the tree.
Almost invariably this is best done either by removing branches completely or by cutting each back to a point at which another branch grows from it. The worst method of pruning trees is to shorten branches equally all over, leaving a mophead of stumps likely to produce a thicket of young stems, like a pollarded willow. The work can be done at almost any time of year except in March-April when the sap is rising strongly and there is a danger that some wounds will ‘bleed’. However, the safest time for pruning deciduous trees is November-February, and for evergreen May-June.