Wait to prune until after several hard freezes, or you risk triggering new growth.
Fall isn't the right time to prune trees and shrubs. There are good reasons to wait till late winter or after the plants' leaves have fallen. Pruning too soon can harm your trees and shrubs.So, when it comes to fall pruning, procrastination is the way to go.
According to gardening expert Mike McGrath, author of Mike McGrath's Book of Compost, and radio host of the show You Bet Your Garden, the rule of pruning is that you should NOT prune in fall. That's right, nothing and no exceptions.
"As soon as trees and shrubs go into dormancy, pruning can begin," he said. "And you can prune up to the time when buds begin to plump up." From mid-November to mid-March, you can shape and thin your deciduous plants in preparation for the spring season ahead.
DON'T prune during fall.
No matter what type of shrub you have, fall pruning can stimulate late-season growth that may not have enough time to harden. This can weaken and damage the plant—especially if there's an early frost. Instead, wait until winter and trim bushes when the plant is in deep dormancy.
Don't shear the branches of spring flowering shrubs (Forsythia, Lilac, New Mexico Privet, Spirea, Flowering Quince, and others). These shrubs produce flowers on last year's wood, so removing old growth will reduce or prevent flowering. These plants should be pruned immediately after they are done blooming.
Avoid pruning shrubs in winter that will bloom in spring.
You'll be cutting off the flower buds that would provide the spring show. The time to prune a spring-flowering shrub is shortly after it has finished blooming, before it forms next year's flower buds.
When is Late Winter? Late winter is 4 to 6 weeks before spring thaw begins. This could be any time in January to May, depending on your climate. Use your average last frost date and count back.
In fact, it is better to prune a little at a time than to make drastic cuts. For plants that shed their leaves (deciduous plants), the best time for winter pruning is from the beginning of November to the end of February. To prune evergreens you can start later, from mid-December, and continue until February.
Pruning in Winter Causes Less Stress for Trees
Research shows that pruning before buds open in spring leads to “optimum wound closure.” Trees are able to heal from pruning cuts before warmer weather brings out destructive insects and pathogens.
New growth won't have time to harden off before freezing temperatures come along. When you prune in the fall wounds won't heal as quickly, leaving the plant more susceptible to fungal diseases. Waiting until after all the leaves have fallen allows you to see the tree/shrub's structure better.
As a general rule, prune spring-blooming trees immediately after they flower. Prune trees that bloom in the summer or fall in late winter or early spring before the end of their dormancy. Routine pruning of dead or dying branches can be done at any time.
In temperate regions, most plants go dormant during the winter. This is the time of year when they've halted active growth and have hunkered down for the cold weather. Because of this dormancy, late winter and early spring are typically the best times to make any adjustments to the shapes of many trees and shrubs.
The best season to prune trees is while they are dormant, or generally between November and March. This means waiting for them to lose their foliage and cease growth, but before forming buds. For fruit trees such as the apple tree, prune in late winter.
Also, do not cut back hardy perennials like garden mums (Chrysanthemum spp.), anise hyssop (Agastache foeniculum), red-hot poker (Kniphofia uvaria), and Montauk daisy (Nipponanthemum nipponicum). Leave the foliage. It's important to protect the root crowns over winter.
You will want to prune your trees when the temperatures are going to be fairly constant for at least a couple of weeks. If you trim your trees when the temperature is 60 degrees, and overnight, the temperature drops below freezing, your trees could be damaged.
Municipalities and homeowners often remove the lower limbs for pedestrian and vehicular clearance or to let the sun shine in for grass to grow. Mature trees, especially evergreens, benefit when healthy lower branches are left intact. Removing large limbs can increase the risk of decay.
Summer flowering shrubs should be pruned in late winter or early spring. This still gives them time to set flowers for the following year. Deciduous shrubs that aren't grown for flowers can be trimmed back at the same time.
Because of the digging involved, you can also rule out winter, when the ground is frozen. Thus, the ideal time to remove large shrubs and bushes is when the ground isn't frozen and it isn't too hot outside.
A rough rule of thumb is to prune spring-blooming shrubs soon after they finish flowering because most bloom on old wood, while those that bloom in summer and fall usually bloom on new wood and can be pruned in late winter or very early spring.