Gardeners are instructed to "cut back hard" a handful of shrubs as spring approaches, that is, cut them down close to the ground. This cutting is applied to shrubs that flower on stems produced the same year, or on "new wood." Although this pruning may seem heavy-handed, if it is performed properly, no harm is done. But don't hack plants back thoughtlessly.
The first season, leave the shrub alone. The following year, when buds swell around mid-April, cut the stems back, leaving two or three buds per stem. Every subsequent year, follow the same procedure. Clean out the deadwood as well. This pruning technique will create a multi-stemmed candelabrum of stumps sprouting a multitude of vigorous new shoots that grow into a shapely and floriferous shrub each year. Caryopteris and butterfly bush, often used in mixed plantings of shrubs and perennials, respond well to this treatment.
The popular butterfly bush, Buddleja x davidii needs little description. The long racemes of flowers at the tips of its shoots are a candy store for butterflies. It often grows much larger than people expect and without proper pruning becomes ungainly. Fortunately, it reacts well to a thorough renovation, which will push plenty of buds from its older wood.
Caryopteris x clandonensis is a modest deciduous shrub showing little promise with its weak, open growth. Suddenly, in mid-August, it creates an airy blue and silvery impression with bundles of small violet flowers that appear in every leaf axil, lasting into September. It is less forgiving of neglect. An overzealous gardener can eliminate it entirely from the garden by cutting it back too hard because, unlike butterfly bush, Caryopteris sprouts very few new buds on the older wood.
By Robert Bartolomei,
Director of Outdoor Gardens and
Peggy Rockefeller Senior Curator