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.
Spring-flowering deciduous shrubs should be pruned with thinning-out cuts, meaning a branch or twig is removed at its point of origin at either the parent stem or ground level. This type of pruning creates a more open plant because it does not stimulate excessive new growth. It also lets you maintain plants at a given height and width for many years.
These types of plants will need little or no pruning the first three years because the plants are still getting up to size. During that time, pruning should be limited to removing dead, broken or diseased branches.
After plants finish blooming the fourth year, providing they are large enough, start renewal pruning. Although the plant will be in full leaf, it won't be hurt.
In gradual renewal pruning, select about a third of the oldest and tallest branches and remove down to the ground each year. Thin them as needed to shorten long branches or maintain a symmetrical shape. For each old stem you remove, a new one will grow back.
If your shrubs are badly overgrown and need considerable attention, you are going to follow the same general procedure but you may need to spend additional years to get the neglected plants back into shape.
Rejuvenation pruning is for plants that are so overgrown and neglected that they cannot be pruned any other way. The entire plant is cut to the ground and then new shoots grow from the base. If you do this radical pruning, you will likely not get flowers the next year and in some cases, the plant may not grow back.
On spring-flowering ornamental trees, remove dead and broken branches but also take out crossing branches, water sprouts and branches that form narrow V-shaped crotch angles.
Larry Sagers is the horticulture specialist for Utah State University Extension at Thanksgiving Point.