Prune flowering shrubs, trees correctly

As a mild-mannered horticulturist, I don't usually get too upset about how other people garden. But I do admit I get upset when I see people abusing their plants by pruning them incorrectly.

So I feel I must speak up and help people understand how and when to prune.

When I ask gardeners to define pruning, their response is, "Cutting off part of the plant." While that covers part of the definition, they almost never add the second part, which is " . . . to produce a desired growth response."

Perfecting pruning skills require learning how a certain plant grows. Since different plants have different pruning requirements, this week's column will focus on spring flowering trees and shrubs.

Perhaps the biggest abuse I see to shrubs and trees come from people who have already pruned those plants. Spring-flowering woody plants should always be pruned after they flower. This allows for vigorous summertime growth and results in plenty of flower buds the following year.

The horticultural reason for this is these plants are grown primarily for their spring color. If you prune them prior to the time they flower, you are cutting off the blossoms before they bloom. While that is not exactly like lighting dollar bills on fire, you are not getting full value from your plants.

Plants that grow in temperate zones — meaning those areas where they go dormant in the winter — have a built-in safeguard. The buds only bloom in the spring when they are going to have a long enough growth period to form fruits and seeds.

Because of this, all spring-flowering woody plants, including fruit trees, form their buds the summer before they bloom. If you prune any time between when the buds form the previous summer and when the plants finish blooming, you reduce the flower quantity.

So why should fruit trees be pruned before they flower? These trees are grown to produce fruit, and pruning eliminates as much as 90 percent of the flowers on some types of trees to divert the energy to the remaining fruit so it will be larger.

Now that we have established the time to prune, the next question is how to prune. For convenience, we can divide these plants into flowering shrubs with multiple stems or trunks and flowering trees with single trunks.

Pruning recommendations for most deciduous shrubs consist of thinning-out, renewal and rejuvenation pruning.