4 Plants You Shouldn’t Prune In Spring: Key Ornamentals To Leave Alone

There are certain plants you shouldn’t prune in spring. It may be tempting to cut them back during your spring cleanup, but you may be sacrificing flowers.

A hand pruning a shrub with shears
(Image credit: Isabel Pavia / Getty Images)

Are there plants you shouldn’t prune in spring? Pruning in spring is “a thing.” You have surely read online that spring is the best time to prune ornamental plants, but is that information correct? Sort of. The best we can say is that the plants to prune in spring rule is neither entirely correct nor entirely incorrect. Some plants are best pruned in spring, others should never be pruned in spring.

So what plants should be pruned in spring? Which plants shouldn’t? Read on to learn more about pruning basics and plants you shouldn’t prune in spring.

Four Plants You Shouldn’t Prune in Spring

A general rule of thumb may help. If a plant blooms before May, do not prune in spring. Here are a few garden favorites that should not be trimmed back in spring. Note that the best time to prune these shrubs is immediately after flowering is done..

1. Azalea

Rhododendron spp.

USDA zones 6-8

If you like azalea blossoms, do not prune azaleas in spring. Azalea are shrubs that flower in spring, which means that they set their flower buds the previous summer. Azaleas can be evergreen or deciduous shrubs and should be pruned at some point between the moment they flower and July 4. The plants are perennials. They grow best with at least four hours of sun every day and moist, acidic soil.

2. Oakleaf Hydrangea

Hydrangea quercifolia

USDA zones 5-9

Hydrangeas are more difficult when it comes to pruning, since some species bloom on new wood, and some on old wood. Oakleaf hydrangea is a perennial shrub with large clusters of long-lasting flower panicles that bloom on old wood. These are plants to prune in fall. Hold off on pruning oakleaf hydrangea until after the flowers fade, although dead or diseased branches can be trimmed away whenever you see them. The plants prefer moist, slightly acidic, well-draining soil in full or part sun or part shade.

3. Lilac

Syringa vulgaris

USDA zones 3-7

Lilacs are popular ornamental landscaping shrubs and turn any garden into a delightful spot, thanks to their showy blossoms. During the three-week blooming period in late spring, the shrubs fill with extremely fragrant flower clusters - purple, pink or white. Lilacs are perennial shrubs. They need good air circulation and do best in a full sun location in moist, well-draining, alkaline soil. You should be pruning lilac bushes in early summer, after the flowers have faded.

4. Forsythia

Forsythia spp.

USDA zones 5-8

Forsythias are a genus of deciduous flowering shrubs that belong to the olive family. These low-maintenance, fast-growing perennials have a graceful, upright, arching form. They are known for their long branches that fill with brilliant yellow blooms early in the spring. Forsythia flowers precede their leaves. Pruning forsythia should take place in the summer, after the flowers have been spent. Plant forsythia in a location with lots of sun and excellent drainage.

When to Prune

Spring cleaning in the garden means raking up winter leaves, taking out weeds, and trimming back some trees, shrubs, and perennials to prepare them for the summer season. Yes, some landscape shrubs and trees should be pruned in spring. These include evergreens, roses, fruit trees, most vines, overgrown shrubs, and summer-flowering deciduous plants. An annual pruning is basic plant maintenance. What happens if you don’t prune plants? Failure to use the pruners in spring can result in too-big or messy shrubs and fewer blossoms. If any of the trees or shrubs have suffered broken branches or are diseased, failure to prune can even cause the decline or death of the plants.

But there are some very important garden plants that should not be trimmed back in spring: spring flowering shrubs. This same rule applies to deciduous trees that are leafing out in spring.

Why Can’t You Prune These Plants in Spring?

Why shouldn’t you prune spring flowering shrubs in spring? It’s not hard to figure out: you will lose some of those gorgeous blossoms.

Keep in mind that not all garden plants set flower buds at the same time. Plants like evergreens, roses, fruit trees, and summer-flowering perennials set flower buds on new wood, that is, the flexible green shoots that appear on the plant early in the growing season. Pruning back these plants in early spring won’t decrease the flower, but rather encourage new wood to grow, which will increase the buds and flowers. These plants usually flower in summer.

But some plants set buds on “old” wood, the wood that grew the prior season. These buds appeared on stems or branches the prior year, and, by spring, are ready and eager to flower. If you prune these shrubs in spring, you will necessarily cut off flower buds and reduce your blossoms. The only time you’ll want to trim these plants in spring is when their branches are damaged or diseased.

As far as deciduous trees go, those that are leafing out in spring should not be cut back. They need that new foliage in order to feed new growth.

Frequently Asked Questions

Which Perennial Plants Should You Not Prune in Spring?

Do not spring-prune any perennial plant that flowers in spring. This includes azalea, oakleaf hydrangea, lilac, and forsythia.

Which Plants Should You Not Prune in Fall or Winter?

Fall and winter is not a good time to prune plants that set their buds on old wood. These plants should be pruned immediately after they flower.

Teo Spengler

Teo Spengler has been gardening for 30 years. She is a docent at the San Francisco Botanical Garden. Her passion is trees, 250 of which she has planted on her land in France.