When are you supposed to prune lilacs? How about forsythia,
weigela, beautyberry and roses? The biggest question about
pruning is when to do it.
The most common question I’m asked about pruning is when to prune a plant. There are different ways or reasons, but the biggest mystery usually is the timing. There are three “times” of year I suggest: after flowering, in the spring and emergencies. You might say those are not “times,” but instances. Nonetheless, it is the easiest way to remember.
This is the first important time to prune. Granted, not all plants flower; therefore, it doesn’t always matter. However, the flowering plants are the ones that usually create the most questions about how to care for them. Consider spring-blooming plants such as dogwoods and magnolias. After they flower in the spring, prune them. If you pruned the plant right after winter breaks or the previous fall, you would prune out the flowers.
Plants are focused on flowering. Take the dogwoods for example: After flowering in the spring they take the summer to grow larger and store energy for the fall. In the fall they produce flower buds that will overwinter for the spring. Fall bloomers are similar, the cycle is just shifted. That is why they are to be pruned in late fall or early spring.
Keep in mind that you can not always say an entire species of a plant blooms at the same time. For example, not all roses or hydrangeas bloom in the spring. Those plants have varied bloom times depending on the exact cultivar of the plant. You either need to research the blooming time or wait until it flowers. Another exception is that continuously blooming plants are safe to prune any time of year.
The second time to prune is spring, for two reasons: You will know what winter damage there is on your plant and it’s the least stressful time of year. Certain plants are not very hardy and will have some damage in the spring, like roses. You want to follow the flowering suggestion and then perform further pruning in the spring if you had winter injury.
As mentioned, spring is the least stressful time of year to prune. The spring usually has plenty of rain and the temperatures are pleasant. These are two main growing conditions that affect whether the plant can recover from pruning. Try not to prune when it is above 80 F if you can help it, especially if it is above 90 F. You want the plant to be able to recover quickly from the pruning wounds by having adequate moisture and moderate temperatures.
This tree shows an emergency pruning need. It is hard to say if the death was from disease, drought or physical damage. Nonetheless, it is a danger to the nearby house and family vehicles. Photo: Nikky Witkowski
This is the last time to prune. “Emergencies” include times of physical damage, insect infestations or disease outbreaks. Quick action is needed and warrants the pruning even if flowering is lost. The other time of “emergency” can be if your plant has unusual growth or reversions. At the top of this page, look at the picture of the weigela that has a reversion on it. The normal plant has the multicolored foliage and stays about 2 feet tall. However, the green foliage can grow larger and crowd out the multicolored foliage, causing you to lose that feature of the plant.
Prune with Confidence
If you follow these three simple suggestions, you can prune your plants at the proper times. If you missed your chance to follow one, it typically won’t harm the plant, just the flowers. The only time pruning is discouraged is during the dead of winter, but emergencies can occur at all times of the year. Just remember these are suggestions that allow your plants to be beautiful and recover the quickest.
Bloom Time of Certain Plants
Spring: Flowering Dogwood, Forsythia, Lilac, Magnolia, Redbud
Summer-Fall: Beautyberry, Butterfly Bush, Chrysanthemum, Cotoneaster, Red Twig Dogwood
*Varied: Annuals, Hydrangea, Rose, Spirea
* These plants either bloom continuously or the species has many different bloom times. For example, smooth hydrangeas bloom at one time whereas bigleaf hydrangeas bloom at another.
Spireas like Double Play Big Bang (left) and roses like Easy Elegance Champagne Wishes (right) often bloom repeatedly throughout the year. Their pruning times are considered “variable.” The Double Play Big Bang spirea blooms on new wood in the summer — grower Proven Winners suggests, “trim as needed to shape and deadhead after flowering to encourage repeat blooming.” Similarly, some roses bloom continuously and some cultivars and species of roses bloom at different times. You must research your roses’ bloom times. The pruning tips for Champagne Wishes at easyeleganceroses.com recommends removing dead or damaged canes and crossing or inward-growing canes in spring, before plants bloom, and deadheading all season. Left photo: Courtesy of Proven Winners Right photo: Courtesy of Baily Nurseries
(From State-by-State Gardening Jan/Feb 2012.)