The trees are donning their brilliant fall colors, the fields of corn and soybeans are being harvested, the last tomatoes and beans are being picked from the garden – fall is here!
These beautiful, crisp, cool days of autumn are when we begin to put our gardens to bed for the season. This has many gardeners venturing out with shears in hand to primp and prune and otherwise tidy up in the garden.
While it is a great idea to cut back some of your herbaceous perennials in the fall, you should keep your pruning shears and loppers away from your trees and shrubs for a while yet.
Why? Because pruning stimulates regrowth. Plants respond to pruning with a burst of new growth; the more severe the pruning, the heavier the regrowth. If this growth occurs during the warm days of fall, the tender new shoots that develop will not have time to harden before the winter cold sets in and they become prone to winter damage.
In general, woody plants should be pruned when they are dormant. This usually means in late fall, winter, or early spring.
How do you know when trees and shrubs are dormant?
It’s easy enough to tell when deciduous trees and shrubs are dormant because they lose their leaves but it’s not as clear cut with evergreens since they keep their leaves through the winter. Luckily, evergreen trees and shrubs normally enter dormancy in the late fall around the same time as deciduous plants.
Not all pruning is done during the dormant period
Though trees and shrubs can always be pruned when they are dormant, there are good reasons to delay pruning of some species. This is especially true when it comes to the spring flowering trees and shrubs. If you prune these during the dormant period, you will be removing many if not all of the flower buds and this will obviously impact the spring bloom!
Many gardeners are tempted to prune their trees and shrubs in the fall as part of their fall clean-up chores – to tidy up scraggly looking or overgrown plants. Before you cut (even if they are dormant), it is important to think about when they flower and the age of the wood that produces the flowers.
Generally, trees and shrubs that flower in the spring form their flower buds in the previous season, usually in the late summer or early fall. These plants flower on “old wood” or growth that was produced the summer before. Because the flower buds are already set on the branches, you should try to avoid pruning them in the fall, winter, or spring. Shrubs like azalea, rhododendron, lilac, some hydrangea, forsythia, viburnum, and trees like dogwood, redbud, and crabapple fall into this category.
The best time to prune these spring bloomers is right after they finish blooming. Pruning at this time can range from simple deadheading of spent blooms to heading back branches and thinning to reshape or reduce the size of the plant. Here are some tips for pruning spring blooming shrubs.
The exception to this rule is if you want to do any heavy pruning. Severe pruning, including rejuvenation pruning where you might cut a shrub down to 12″ to 24″ or lower, should be done when the plant is dormant – usually in March. Obviously you must sacrifice the bloom for that season and possibly the following season as well but in most cases, you will be rewarded with a beautiful “new” shrub. Not all shrubs can be pruned hard like this so be sure to do some research before you start chopping!
Summer flowering trees and shrubs form flower buds on the new growth that is produced in the spring and summer. These are normally pruned in the spring before growth begins. However in colder regions, we often recommend that you delay pruning until the threat of very cold weather is past. This sometimes means pruning after growth has begun but don’t worry, it won’t hurt the plant.
Summer is a good time to prune certain trees and shrubs if you don’t want to encourage a lot of new growth. As I mentioned earlier, pruning stimulates growth, especially when it is done in the spring. Pruning in summer has a dwarfing effect because growth is slower at this time.
For instance, summer is a great time to prune water sprouts – those vigorous stems that grow straight up parallel to the main stem. Pruning them out in the summer can reduce the number of water sprouts that will develop the following season.
Summer is also a good time to prune trees that are heavy bleeders like maple, birch, and dogwood. It is best to avoid pruning these trees just before and during active growth in the spring because they have a heavy sap flow at this time.
A good pruning book will give you recommendations on the timing and techniques for pruning specific trees and shrubs. A handbook like this is a valuable addition to your gardening library.
For more pruning tips, visit our website.