Know your spring-blooming plants before pruning

Q. When should I prune my spring blooming trees and shrubs so I don’t lose next year’s flowers? The flowers are long gone.

Keith from Poland

A. Trees and shrubs which bloom in the spring should be pruned when they are done blooming. Examples are lilac, azalea, rhododendron, forsythia, crabapple, dogwood and weeping cherry. These plants bloom on old wood, meaning the plant sets the bloom in August for bloom the next spring.

The blooms almost always survive our winters, but in some cases, extreme cold can kill the buds of plants such as forsythia. If you trim these plants in late winter or early spring, you are cutting off the blossom buds.

Plants that bloom in late summer, such as butterfly bush and some hydrangeas bloom on new wood. These plants can be pruned in late winter or very early spring. Thus, knowing the name and cultivar of your plant will help you prune at the correct time.

One of the most common questions coming into the diagnostic clinic is, “How do I get my hydrangea to bloom?” Well, some hydrangeas bloom on new wood and some on old. Some do both. Knowing what you have is imperative to proper pruning and seeing the blooms.

Pruning is done for many reasons. It is mostly to maintain the health and appearance of your flowering shrub. Removal of dead or damaged branches will help to maintain a healthy shrub. Most people tend to shear. This is usually because the plants are large and unruly. That should not be your main reason for pruning. Pruning is not a substitute for proper plant selection – choosing a plant that fits the height and width of the space in your garden.

Thin instead of shearing. Thinning is a process of removing stems at their point of origin. It is also called selective pruning. This is the preferable way to prune because it opens up the plant to increased sunlight and air circulation.

When you cut a few inches or a few feet from the top of the plant, you are encouraging new growth at the site of the cut. This sometimes results in a condition called “witches broom.” This is when one stem turns into 4-5 stems, causing an explosion of growth at the tips. This blocks the sun and air circulation for the inside of the shrub.

If you are rejuvenating an overgrown shrub like lilac or forsythia, remove the biggest and oldest stems at ground level after blooming. Keep the sturdiest, well-placed younger stems and remove those that are damaged, spindly or too close to one another. Doing this will help to keep your plants healthy and beautiful!

For more information and pruning tips, visit

Today’s answer is provided by Barb Delisio, OSU Extension master gardener volunteer. Call the Mahoning County office hotline at 330-533-5538 to submit your questions. Regular clinic hours are Mondays and Wednesdays from 9 a.m. to noon.

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