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What to Prune Before May Is Over (And What to Leave Alone)

By Jenna Clark Dengarden

Updated May 15, 2026 8:53 AM

My wife trimming the forsythia bush in our garden. Work to do in spring. Photo by Dmitrii Marchenko on Getty Images

While you might find yourself preparing to prune some of your garden plants in May, you want to ensure you're pruning the right ones, as incorrectly doing so (or pruning the wrong plants) might cost you (and your plants). Pruning can be an essential part of plant care when carried out properly.

"Pruning is important to give the plant a uniform, cloud-like appearance and also to thin the shrub out to increase airflow through it," says Nathaniel Neufer, arborist at the United States Botanic Garden. "An open, airy plant has fewer problems with insects and disease than a congested plant."

Even though it might be tempting to cut every unsightly branch you see with your pruners or scissors, you should only remove what is necessary. "One of the hardest things to do is not over-prune," says Barbara Arnold, senior horticulture designer at Franklin Park Conservatory and Botanical Gardens. "Once the branch is removed, it can't be put back on." John Faerber, director of horticulture, landscaping and floral at The Lake House on Canandaigua, adds that using clean (and sharp) tools is key to getting the job done as effectively as possible.

We chatted about gardening and horticulture experts Neufer, Faerber, Arnold and several others, to learn more about which plants you should be pruning throughout this month. We also asked them for their insights regarding pruning best practices and what can happen to your plants if you skip pruning altogether (or do it at the wrong time). Furthermore, we inquired about which plants you should let be throughout the month.

arena photography — Igor Paszkiewicz / Getty Images

Read on for five plants that require pruning in May, so you can keep them both breathing properly and looking nice into the start of summer and throughout their flowering season.

1. Azaleas

May is the perfect time to prune any azaleas in your garden. "If these are pruned during the winter or too late in summer, you could remove the flower buds, and the plant will not bloom in the spring," says Neufer. That said, our experts note there is a specific method you should follow when pruning. "They have a whorled branching habit, so the best way to prune them is by identifying branches that are breaking out of the desired form and prune them back to a whorl on the interior of the shrub," he says. "They can also be thinned by removing entire branches to the ground if need be."

With this in mind, Dr. Kimberly Moore, associate center director and professor of environmental horticulture at the University of Florida, IFAS, Fort Lauderdale Research and Education Center, adds that you'll want to do some light shaping.

2. Gardenias

Moore notes that May is often a good time to prune gardenias since they have already flowered in many areas. "Prune right after flowering to shape the plant and remove leggy growth while preserving future buds," advises Moore.

3. Deutzias

Arnold recommends pruning your deutzias after they have flowered (if they have) in May. "Deutzias have very visible branches that need to be removed," she explains. "Remove any branches with spent flowers along with minor branches that didn't leaf out in spring."

While there's no real risk to not pruning your deutzias in May, she notes you'll likely appreciate the cleaner look and shape if you do.

4. Forsythia

Neufer notes that forsythia requires pruning in May to remove dead stems and prevent overgrowth as these flowers bloom on old wood. "Look for dead/diseased stems to remove first, then thin out the largest, oldest stems to the base," he says. "Then shape the plant to the desired size by pruning back to a lateral branch or node along the stem. Prune branches that are growing into the center to try and achieve a vase shape, with stems growing outward from the center."

Tip: Don't prune these shrubs before they bloom.

5. Lilacs

It's not surprising that you may find yourself wanting to prune lilacs in May (and, Arnold notes, you should) as these plants also bloom on old wood. That said, she explains that you'll want to keep your pruning efforts on the lighter side unless you find yourself needing to revive your plants. "May pruning for a lilac is a simple clean-up job, removing spent flowers and any minor branches that didn't leaf out in spring (there shouldn't be that many)," she says.

What Plants You Should Not Prune in May

While it's important to know which plants to prune in May, it's equally important to know which ones to leave alone. Arnold notes that you should avoid pruning trees and shrubs that flower in the summer. Furthermore, Moore advises against pruning Crape Myrtle, as you risk removing flower buds, which could reduce your summertime yield.

In addition to Crape Myrtle, Faerber says you should leave flowers such as peonies and irises alone this month to prevent damage and ensure they're healthy as they continue to grow and bloom.

This story was originally published May 15, 2026 at 8:15 AM.