When to prune shrubs

By Alan Jolliffe

Pruning time depends on the flowering season of the shrubs. The method of pruning depends upon whether the flower is borne on the new of the old wood. For pruning purposes, shrubs can be grouped in six classes:

1 For shrubs where the new shoots (those of the current year) bear the flowers, pruning should be done at any time in winter as the flowers usually arrive in summer or early autumn. The shoots of the previous year are pruned hard back to the structural branches of the shrub or even ground level. Sufficient old wood (it must not be too old) must be left in to form a structure to carry the new growth. This does not apply to shrubs that send up new wood directly from the ground level.

2 Where the plants flower on the wood made during the previous summer, pruning is done directly after flowering, as it is vital to give the plants as much time as possible to form and ripen new wood before winter. This is the wood flowers will be borne on the next spring. Some earlier flowering plants may be thinned, the old flowering shoots removed and pruned sufficiently to keep them tidy and trim.

3 The third group consists of those shrubs that flower in spring and onwards through the summer on the wood produced during the previous growing season.  These shrubs start to make much of their new wood before the flowers fade. Much of this new growth would have to be cut away with the old wood if the pruning were left until after the flowering season. Shrubs of this group should have the oldest wood cut right from the base early in the autumn. This will give the new wood a complete growing season in which to develop. When a shrub is pruned in this way, it will sometimes make so much young growth that a thinning out of this new wood may be necessary during the summer.

4 This group comprises shrubs whose blossom is borne on wood over two years old, or on short "spurs" from it. With this group of plants very little pruning is needed in the ordinary way, but the young growth must be cut back annually in winter to within 75mm of the old wood. Very old wood and weak growths should be cut out annually.

5 There is another group that consists of plants that throw up vigorous young growth direct from the roots. Some of this class flower best on the old wood, and most of the young growth must be cut away annually. But where the best flowers are borne on the young wood, and in cases where the plants are grown for their foliage or coloured stems rather than for bloom, they should be cut down almost to the ground each year.

6 The last group is composed of slow-growing shrubs that need no pruning. They may need light pruning to develop a nice shape but once mature they will require no pruning except for occasional thinning when overcrowded, or trimming should any of the branches become straggly.

Sometimes when a shrub has been in the same position for several years, the wood becomes thin and weak, and blossom is poor and scarce. Should this happen cut the old wood out and the newer wood hard back. Do not cut out all the old branches at once, remove an entire branch at a time, one every year in late spring.