Pruning Trees and Shrubs in Late Spring
Mid-spring pruning should be finished as soon as possible; the main group of shrubs to be pruned during this season are those flowering from early spring to the middle of late spring, as named in the following list. You can do some pruning when cutting flowering sprays for the house; make sure that the cut is made just above a strong, new shoot.
Cut some of the oldest shoots down to ground level, cut flowered shoots back to strong new growth and thin out the remainder. This need only be done every three years or so.
The montana types can be cut back hard immediately after flowering to leave a few centimetres (inches) of the flowered growth every year or they can be pruned every four years or so in the same way, but further back, to the oldest growth. If C. alpina and its varieties needs treatment, do it after flowering, to thin out the oldest shoots and cut back others to strong new growth, also every few years. C. armandii can grow extremely large against a sunny wall but is a little tender, and does not take well to any more pruning than occasional thinning out and cutting back to the space available.
Virtually no pruning needed, as its habit of growth is naturally tidy and well-spaced but occasional removal of weak shoots and those which are old and hardly flowering improves its appearance even more.
If late in flowering or not yet pruned, forsythia should be pruned now; remove flowering sprays and thin out remainder.
A charming shrub, with its white chimneysweep’s brushes of flowers, it hardly needs any cutting beyond the removal of dead shoots, weak ones and any which cross or are too close to each other.
Tree heathers, spring-flowering (Erica arborea, E. australis, etc.)
These can be left alone and will still flower well but are bushier and more floriferous if cut back after flowering by about 30-60cm (12-24in).
The oldest shoots or spurs can be removed altogether after flowering, some of the flowered shoots cut back by about half and a little thinning done.
Those grown as wall shrubs should be pruned to produce spurs; cut back the flowering shoots after flowering to leave one or two buds.
Virtually no pruning is necessary, except to cut the oldest shoots down to about half their length occasionally.
If plants have become gaunt and leggy and if you live in a mild district, you can cut them down hard at the end of this season. This treatment may prove fatal, if the weather turns cold unexpectedly, but as they root so easily from layers or, pruning is probably not worth the risk involved.
Leave well alone and do not prune except occasionally to remove dead and diseased shoots, broken ones and weak or crowded ones.
Spiraea x arguta
Cut off some of the flowered shoots after flowering, back to strong new or potential new growth. Remove some of the oldest growth to ground level.
Tamarisk (Tamarix tetrandra)
Little pruning needed but cut back some of the flowered shoots to new ones, to keep the size under control.