Advice
RHS Help & Advice
Pruning and training ornamental trees
Purchasing
Most trees available from garden centres and nurseries will have been pruned in the nursery to produce a good branch structure and shape. However, individual trees will vary in their quality and it pays to take a little time to check them out; view from all sides. Ensure the main branches are strong and sound and that existing pruning cuts are well healed. Avoid trees which have competing leaders with two or more main shoots.
Most ornamental trees are pruned and trained as feathered trees or as standards. After the first two or three years little further pruning should be necessary if the tree has been chosen to fit the situation. The commonest mistake is to choose a species which is too vigorous for the size of garden. Where regular heavy pruning is needed to reduce height and spread the wrong tree has been planted in the wrong position.
Feathered trees
A feathered tree is one with a single main stem with lateral shoots almost to the base. This is the typical growth pattern for silver birches, poplars and alders. For this type of tree it is important that the leader is retained. Do not allow a forked or double leader to develop as this will create a point of weakness.
A feathered tree will branch naturally and symmetrically on its own. Only if a lateral is badly placed or likely to unbalance the overall shape is any pruning needed. Such pruning is best undertaken in early winter following leaf fall.
As the tree develops, the lowest laterals can be removed to leave a short, clear stem. However, do this in stages over two or three years as retaining the lower laterals helps to thicken up the main trunk.
Standard trees
The standard is the most widely available form used for ornamental trees. The main stem is clear of branches for the first 1.8m (6ft) or so. The crown of the tree will either be developed with a central leader or as a branched head. The central-leader standard is similar to a feathered tree but with the lowest branches 1.8m (6ft) from the ground.
With the branched-head standard there is no central leader. This form is particularly popular for small ornamental trees such as cherries and crab apples, but is not suitable for large trees. Once the appropriate length of clear stem has been formed, the leader is cut back in early winter to encourage laterals to form the main framework. The branches should be evenly spaced and any crowded or crossing branches cut out. Further pruning is largely confined to maintaining a balanced, even shape. Remove any vigorous upright shoots which may form a new leader and any side shoots that develop on the cleared trunk.
Weeping trees
Some weeping forms of trees are grafted or ‘top worked’ on to stocks with stems up to 1.8m (6ft) to produce weeping standards. Common examples include weeping ash (Fraxinus excelsior ‘Pendula’) and Kilmarnock willow (Salix caprea ‘Kilmarnock’). Pruning should be restricted to removing shoots that spoil the outline - cutting upward-growing shoots back to a downward-pointing bud and cutting out crossing or congested growth. Ensure that any shoots that spring from the trunk are pinched off while the growth is still soft.
Broadleaved evergreen trees
Broadleaved evergreen trees usually require only minimum training as young plants and are best treated as feathered trees. A strong central leader should be established and badly placed laterals or competing leaders cut out during the early years of growth. Little further pruning should be necessary.
Conifers
The feathered tree technique is also applicable to most conifers. The basic growth pattern of pines and firs is for a single central leader to grow with branches developing at fairly regular intervals along its length. They generally should not need pruning. Unlike broadleaved trees, conifers (with the exception of yew) will not regrow from old wood. Any pruning of mature conifers should be restricted to removing entirely dead branches. Attempts to reduce them in height will simply mutilate the tree. If the terminal bud dies or is damaged, use a cane to train in the best placed lateral as a replacement leader, cutting out any competing upright shoots.
Multi-stemmed trees
Some species, such as birch, can be cut hard back to near ground level to encourage several new stems to develop. However, this technique cannot be used with grafted plants. In the second winter remove surplus stems. In subsequent years laterals can be left or the lowest ones removed to show off attractive bark.
When to prune
Most deciduous trees are pruned when dormant in late autumn or early winter. Several species such as maples (Acer) and birches (Betula) bleed badly if pruning is left to late winter. Magnolias are pruned in mid-summer as winter pruning wounds are slow to heal. Cherries (Prunus) are also pruned when in leaf to avoid the danger of infection by the disease silver leaf. Evergreens are usually pruned in mid- to late summer.
Pruning techniques
The formative training and pruning of young trees should be within the capabilities and resources available to the home gardener. However, pruning of larger trees is potentially dangerous and should always be left to qualified professionals. If you are seeking a tree surgeon contact The Arboricultural Association.
Tony Dickerson