More shrubs and trees are probably prevented from flowering by being pruned wrongly,
than are helped by being pruned correctly. 'If in doubt, leave it', should be the
novice pruner's motto. Wild shrubs are never pruned by gardeners, and are often well
covered in flowers.
The purpose of pruning should be to either improve the shape of a shrub or to
encourage it to flower better. Minor shaping is best done in spring, or after
flowering for spring-flowering shrubs; before growth begins for summer-flowering ones.
Really drastic pruning of deciduous shrubs is best done in autumn after the leaves
have fallen, while the plant is dormant, or of evergreens in early spring when the
plants are less active.
When pruning for better flower production it is important to know whether the flowers
are produced on the stems made the previous year or on the new wood formed during the
current year. Further, some shrubs flower best on vigorous shoots, others on
Shrubs which flower well on slow-growing wood formed the previous summer include
Rhododendrons, Magnolias, Ribes, Lilacs, and most evergreens. Every healthy growing
shoot ends in a bud or buds, if conditions for bud setting have been suitable at the
end of the previous summer. No pruning is needed and if flowering is not prolific,
the shrub is either not growing happily, or not getting the right temperatures in
summer. Many shrubs of this type do however benefit greatly from the removal of
the dead flower heads as soon as they have faded, and especially if flowering has been
prolific. If they bear a heavy crop of seed they may flower well only every other year.
Shrubs which flower best on vigorous stems produced the previous summer include
Forsythia, Philadelphus, Deutzia, winter and spring-flowering Buddleias, Cestrum
elegans and some Clematis. They respond to pruning immediately after flowering,
taking out stems that have flowered to encourage strong, new growth from below,
and removing also some of the weakly ones that may be developing.
Shrubs which flower on new wood formed during the current year are mostly late
summer- or autumn-flowering and include Fuchsias, some Hydrangeas, deciduous
Ceanothus, late-flowering Buddleias, Cestrum parqui and some late-flowering
Clematis. They are best pruned in early spring and can mostly be cut back quite
hard to encourage strong shoots that will flower well. Cuts are usually made just
above a healthy bud, towards the base of the previous season's growth.
Some shrubs do need special pruning: Wisterias should have the long twining shoots
shortened to about six buds, usually about four inches from the old wood, in July or
about two months after flowering. They may then have a second flowering, less good
than the first; these flowered shoots, and any later twining shoots, should be cut
back to two or three buds in early autumn, to encourage bud production for the
following spring (if sparrows do not take the buds during winter). Pruning of
Clematis is usually done in early spring or immediately after flowering.
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