A Primer on Pruning

One of the most perplexing questions facing gardeners is knowing when to prune. As a general rule summer- and fall-blooming shrubs and vines should be pruned in late winter while the plants are still dormant, while spring-flowering ornamentals should be pruned right after bloom before next year's buds have set. Most of the cuts made at this time will be heading cuts unless a branch is so unhealthy it must be removed entirely with a thinning cut. Some vigorous growers, such as wisteria, will need regular pruning throughout the growing season to keep them under control.

Heading

A bud on a branch is a point of growth, and the terminal bud, or growing tip, has the most energy, dominating growth on the branch of a tree, shrub, or plant. When the terminal bud is removed, the energy for plant growth is directed toward the remaining buds. This method of pruning is often referred to as a heading cut. And most gardeners are familiar with its results, such as when they pinch out the growth of a petunia to encourage the growth of side shoots and increased bloom.

Deadheading, a variation of heading, removes spent flowers to increase the attractiveness of plants and to prevent seeds from developing. The plant's energy is then redirected toward more growth or repeat flowering. The removal of smaller side shoots (disbudding) may produce larger, lusher blossoms on some herbaceous perennials, such as peonies, gloriosa daisies, and chrysanthemums. These are usually heading cuts, since only the flower and a minimal amount of the stem are removed.

Sharp loppers, saws, or pruning shears are necessary to make clean cuts without tearing or damaging the stem or bark. A heading cut should be made about 1/4" above a bud chosen because of the direction it faces. Pruning roses above outward-facing buds will cause them to branch out beautifully, rewarding the gardener with healthier plants and more profuse blooms.

Thinning

The other basic pruning cut, thinning, involves the removal of an entire branch to its point of origin. If a viable bud remains at the original point of growth, a replacement branch may develop, or the plant may just heal over the pruning cut and direct its energy toward the remaining branches. When making a thinning cut, be careful not to damage the branch bark collar, that is, the rings at the base of the branch.

Neglected older trees and shrubs can be a challenge for the gardener. A few thinning cuts to remove weak growth may be enough to allow increased light to the plant, renewing bud development and growth on the remaining branches. If not, a few careful heading cuts will renew vigor and increase vegetative growth. Late winter pruning of older shade trees, fruit trees, grapevines, and berry shrubs is ideal-it reshapes the trees or shrubs while they are still dormant and brings us into the garden before spring weather reminds us of other garden activities.

Thinning cuts may also be required where winds and weather have damaged plants, forcing the removal of injured limbs. But the vigorous growth that follows heavy pruning may not always be desirable. In these cases, the removal of some growth with thinning cuts during the growing season will help redefine the plant's shape.

A beautiful old garden with lovingly tended plants speaks of generations of gardeners who cared enough to study each plant as an individual specimen before changing its growth and shape with thoughtful pruning cuts. By pruning your plants as they need it, you'll be ensuring that they will remain healthy and happy in your landscape for years to come.