When to prune?

Hydrangea pruning
Hydrangea pruning

The mild fall weather has brought an influx of pruning and trimming questions. I thought I might take a moment to share a few tips, reminders and how-to advice.  Without a doubt one of the most frequently asked pruning/trimming questions we receive is, “When is the best time to prune my ________________ bush(es)?”  Our answer varies greatly by the kind of plant that fills in the blank.

Tor Birchleaf Spirea
Tor Birchleaf Spirea

For the majority of our deciduous/leafy, summer-blooming shrubs, such as spireas, potentilla, ninebark, and smokebush, you have a few options.  Pruning in early spring, once growth begins; summer, after they are done blooming; or in the dead of winter, when they’ve gone dormant.

Dwarf Korean Lilac in full bloom.
Dwarf Korean Lilac in full bloom.

When working with deciduous, spring-blooming shrubs like, forsythia, lilac, rhododendron/azalea, and magnolia, the best time to prune is quite different. Take a look at the branches of these spring blooming varieties. You’ll notice knobby buds on the tips of their branches.

Forsythia in full bloom
Forsythia in full bloom

For these plants to “burst forth” in spring, with flowers no less, they had to prepare themselves this season. Not only would pruning these plants in fall or winter sacrifice their flowers for the coming spring, but so much energy has been spent preparing those buds that aggressive pruning or all over trimming can stress these plants to a point they are unable to recover from. The best time to prune and shape your spring blooming shrubs is after their flowers have begun to fade, or just after they have completed their bloom.

Fruit producing shrubs can only produce if the flowers are allowed to be pollinated and left to mature to fruit. By pruning plants such as, chokeberry, dogwood, cranberry, or viburnum, once they have finished blooming, you may be trimming off the fruit you were hoping to enjoy later in the season.  We would recommend pruning these once their fruit has set so that you have the opportunity to enjoy the seasonal interest provided by these plants.

Quick Fire Hydrangea fall color
Quick Fire Hydrangea fall color

Hydrangeas can bloom on old and new wood which makes them far less fussy over the time they are pruned. We do recommend that you trim off the flower heads in the fall or early winter before the weight of winter snows can collect on them causing breakage.

Arborvitae are a popular evergreen for screening and structure. The best time to trim them is based on personal preference. If you prefer the natural soft look of arborvitae, then we would recommend that early August be your trimming deadline. Not because it will hurt them to prune them later, but because you need to allow enough time before they go dormant for some new growth to emerge.  By trimming or shearing them back later in the season, once growth has stopped for the winter, they will maintain that freshly sheared appearance all winter long with no new growth to provide the visual softening mentioned above.

Technito Arborvitae, Photo courtesy Bailey Nurseries
Technito Arborvitae, Photo courtesy Bailey Nurseries

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