"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.
Any gardening expert will tell you, (contrary to what you may believe) that pruning encourages new growth just when the plant is trying to go dormant and new growth doesn't have enough time to harden before the first frost and freezing temperatures hit. Pruning at this time of year will severely weaken the plants.
For most trees, the best time for major pruning is late winter to early spring because wounds close faster. Pruning in late summer and early fall may also stimulate new growth, which has little time to harden before cold weather comes.
Future frost events will kill the tender new growth and possibly the entire plant. You may not want to, but you should leave those ugly dead leaves in place through the winter. Wait to prune until the threat of frost in your area has passed and evidence of life within the plants is visible.
It is best to wait until the trees have been exposed to freezing temperatures and until the leaves have begun to turn yellow before beginning early dormant pruning. Keep a watchful eye on the long range forecast and suspend pruning when a severe drop in temperature is forecast.
Don't prune too late in northern regions.
In areas with cold winters, avoid pruning after the middle of August. If you prune too late, you may stimulate new growth that would not have time to grow thick, protective bark before the killing frosts of winter.
Plants are more brittle in cold temperatures. Messing around with them may cause branches to snap and split unintentionally. It's minor, but it could impact the look of a plant or create a haven for insects and diseases later. Don't prune when the temperature falls below 25°F.
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.
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.
Late winter is a good time to prune most plants. Because plants and their pests are dormant this time of year, pruning cuts can be made without the risk of pests and pathogens entering the tree through the wound.
Generally, the best time to prune or trim trees and shrubs is during the winter months. From November through March, most trees are dormant which makes it the ideal time for the following reasons: Trees are less susceptible to insects or disease.
Avoid pruning in fall.
Trees and shrubs reduce their energy production as the growing season ends, so new growth in autumn will use a plant's stored energy reserves. Dieback from a freeze means that energy used for this growth was wasted.
Choose the Right Time
Likewise, prune in the early morning or late afternoon to avoid the newly cut ends of branches becoming scorched by the hot sun. Wait 48 hours after rain to prune, to allow plants to dry out and avoid fungal diseases. When pruning, make cuts just above leaf nodes, or buds.
Spring flowering shrubs and trees.
Shrubs and trees like lilacs, azaleas, and others will grow best when they are pruned right after they flower in the spring. Avoid pruning them in the winter as it may stunt their growth.
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.
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.
Maples. Along with birches, elms, and other so-called "bleeder" trees, pruning maples in winter can lead to a great deal of sap. Wait until summer to avoid a possible mess.
Pruning Too Early
If you prune too early in the season, there's a good chance you'll snip the buds right off their branches, which means no flowers in the spring. Before you cut, do a little research, like with our pruning guide, or just wait to trim until the plant has finished blooming for the year.
When is the Best Time of Year to Prune Trees? There is never a bad time to remove dead, damaged or diseased branches. But most trees benefit from pruning in mid to late winter. Pruning during dormancy encourages new growth as soon as the weather begins to warm.
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.
Never prune too early in the winter, as incisions can dry out if the temperature drops well below freezing. When pruning, first prune out dead and diseased branches, especially those caused by the winter's snow and ice. Unwanted lower branches on all evergreen shrubs and trees should also be removed in late winter.
A good rule of thumb is that if the plant blooms on new growth, it can be pruned in winter, before the new season's growth begins and after the final bloom of the year. Be careful with spring-blooming shrubs—those usually can't be pruned in winter without damaging the flower buds and ruining the blooming season.
The best time to prune is after flowering. If the plant needs to be renovated, or severely reduced, this can be done late winter and early spring just before growth begins.