As with any other skill, it’s easier to learn how to prune if you first understand why you are doing it. Pruning is necessary to maximise the flowering or fruit-production of a plant; to encourage it to grow into appealing shapes; or to manipulate the way in which it grows in order to emphasize its most attractive features. Many deciduous shrubs produce colourful stems or interesting foliage but will only continue doing this is if they are properly pruned.
The dogwoods, Cornus alba, C. sanguinea and C. sibirica, are grown for the vibrant colours of their naked stems in winter. As the stems age and become woody, the colour fades, so not pruning the plant will result in a tall shrub with dull branches at the bottom and colourful stems at the top. Regularly cutting the stems back will encourage colourful new growth and create a compact shrub.
Leave newly-planted dogwoods to become established for a year before you do any pruning. The first year after planting cut half the stems back to the base, leaving about 5cms of stem at the stump. You don’t need to worry about cutting back to a bud. Do it in late spring, just before the shrub starts to produce leaves, and strong new shoots will start to grow within a few weeks. The following year remove the stems you left but not the ones that have been produced during the current season. You will be able to tell the difference by the brightness and suppleness of the new growth. In subsequent years the shrub will be strong enough for all of its stems to be removed each spring, giving you masses of fresh, brightly-coloured stems. On old plants, even new stems can become thick and woody, so you may need to use loppers rather than secateurs to cut them.
Continually producing new stems requires a lot of energy from a shrub, so it is important, after pruning, to mulch around the base of the plant with compost or well-rotted manure. If you don’t do this you will end up with weedy, thin stems. The exceptions to this annual regime are Cornus sanguinea ‘Winter Beauty’ and Cornus sanguinea ‘Midwinter Fire’. These are not as vigorous as other cultivars and, once they are mature, should be cut back every two or three years, rather than annually.
The white bloom on the ghost bramble, Rubus cockburnianus, is also most striking on young stems. Rubus does not form a trunk-like base in the way that Cornus does, so it can be cut back to ground level. Once again, this should be done in early spring, taking great care not to get hurt by the vicious thorns. I usually cut away the top half of the stems first, take them to the shredder, and then go back to remove the rest. You get fewer scars that way. Once you’ve done this you will be left with the stubs of the bramble, poking sadly out of the ground. It may seem improbable, but by the end of the season the new stems will be as long as the ones you’ve just removed.
Pruning willows in this way, not only encourages colourful branches but keeps the plant to a manageable size. Stems can either be cut back to a stump, as described above, or to a short stem. A year after planting remove all the stems apart from one upright one. Cut this horizontally at the height you want the new stems to shoot from ( I cut mine at about 1m). You will need to use a pruning saw to cut through the wood. The new shoots will sprout at this point. You may get growth appearing lower down the stem and from the base. These can be rubbed out with your fingers when they first appear or, if you don’t notice them early enough, cut off close to the trunk. This technique is useful in smaller gardens because it allows you to use the space underneath the willow for spring bulbs and low-growing perennials.
Cutting back trees to the ground in the spring, known as coppicing, encourages the tree to produce new shoots from its base. These juvenile shoots often have much more decorative foliage than mature ones. When the foxglove tree, Paulownia tomentosa, is coppiced each year it has leaves that reach 60cms across on shoots 2.5m tall that are popular in jungle-style gardens. Forcing Paulownia to continually produce new shoots does, though, sacrifice its flowers, which only grow on mature trees. Similarly, treating Catalpa bignoides, the Indian Bean tree, in this way will produce beautiful foliage but no flowers and therefore no beans.
The juvenile foliage of Eucalyptus is also more attractive than the mature foliage. After the tree has been planted for a year it can be coppiced, to create a fountain of new growth each year. Alternatively, leave the stem to reach about 2m – 3m tall and then, in the spring, cut the main stem at about 2m and remove any lower branches, cutting them flush with the stem. You will be left with something resembling an ugly tree stake but, within a week or so, small buds will erupt along the stem. Leave the buds that form on the top 10cms of the stem, and rub off all the rest. A few weeks later they will have grown into new stems, leaving you a clear trunk topped with eye-catching foliage.
Use the right tool
Secateurs will cut stems up to 2cm wide, loppers will cut double that. With both secateurs and loppers the branch to be cut should be placed as deep in the haws of the blade as possible. If you need to strain or twist the cutters you really should be using a saw. General-purpose and carpenter’s saws are designed for cutting dead wood and are not suitable for pruning. Pruning saws have teeth that are side wide apart so that the sap and sawdust don’t clog the saw. They usually cut on the downward stoke, as you pull the saw towards you. After you have used the saw it will have sap and tiny pieces of wood in the teeth which you should wipe off with a cloth.
Shrubs that can be cut back to the ground
Shrubs that can be cut back to the ground or to a short trunk
Cotinus coggyria & Corylus can be treated in this way but should only be cut back every three to five years.