Pruning can be good for shrubs

Warmer air and sunny skies spur that primal urge to get out and play in the garden. Pruning shrubs is a good place to start. Most need annual pruning and are forgiving of mistakes.

Shrubs generally lack permanent trunks; instead, they constantly grow new stems near ground level to eventually replace relatively short-lived older stems. How long the stems live and how many new sprouts a shrub grows each year go hand in hand, and varies from plant to plant.

Prune mostly to help your shrub renew itself. Cut away oldest stems to clear the way for, and stimulate growth of, new stems. Many flowering shrubs blossom only on stems that grew the previous season, so ample growth this year is needed for a good show next year.

Don't wait for an old stem to become totally decrepit before cutting it away. In fact, every year cut the whole plant down to the ground in the case of butterfly bush, Hills-of-Snow hydrangea, Russian sage, and St. Johns Wort. All these shrubs flower only on vigorous new shoots, so old wood is not needed at all. Be almost as severe with kerria, snowberry, and other shrubs that flower best on stems that grew last year. Lilac, mock orange, and forsythia are among shrubs that also flower on one-year-old stems, but on one-year-old stems growing off higher in the plant, so their older wood can stay a bit longer before being cut away.

Once you have cut away some or all of the oldest stems from a shrub, turn your attention to the youngest ones. If they are crowded, cut some to the ground to leave room for those that remain. Start with those that are spindly, broken, or diseased.

Do you still have the urge to prune? Then look over your shrub and shorten or cut away any stems drooping to the ground, as well as any still overcrowded in the center of the bush. Also step back for an overall look, so that you can correct any wayward stems throwing the plant out of kilter.

Some restraint is in order. First, wait to prune spring-flowering shrubs until after their blossoms fade, or else you will be removing stems with blossoms you might otherwise enjoy. And second, shrubs such as pagoda dogwood, witch hazel, and PeeGee hydrangea have long-lived stems and send out few new shoots, so need little pruning.