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.
In February, harmful tree diseases are at a minimum and deciduous trees have already “hardened off”, meaning they have prepared for winter dormancy. When the growing season begins, the wounds will be sealed, and the healing process will begin. July and August are the second-best times to prune.
Pruning during the active growing season can cause stress for your trees and can stimulate additional growth that won't be able to harden before the temperature drops. Trees go dormant during the winter months, making it the perfect time to prune. With extra energy reserves, trees are able to heal more quickly.
That's especially for oak and elm trees! If possible, you should not prune oak trees at all during the summer to reduce the chance of oak wilt, which is a potentially fatal disease, and do not prune elm trees at all during the summer to reduce the chance of Dutch elm disease, both of which are fatal diseases.
Your Tree Will Look Better in Spring
Any branches cut back during the winter will be able to recover quickly in spring with new growth. This will also minimize the amount of time you'll spend looking at a plant that looks like a bunch of sticks after rejuvenation pruning.
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. The lack of leaves after autumn allows you to easily identify branches and limbs requiring removal.
Avoid pruning in fall.
Pruning cuts can stimulate new growth that, unfortunately, will be killed as temperatures drop to freezing. 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.
Tips on Summer Tree Trimming
The warmer months are a great time to do some structural cleanup. Remove suckers, water-sprouts and branches that are crossed or rubbing each other. Take out “the three Ds” where you see them, too, (aka dead, diseased and damaged wood).
Answer: In general, pruning a tree when it is dormant is recommended if there are large branches to remove; that is, pruning between the time the leaves fall from the tree in the fall and the time the buds swell in the spring. However, pruning for safety reasons or minor pruning may also be done in the summer.
Summer is an excellent time for restorative pruning. You can correct problems that have resulted from over-pruning or poor pruning. You can also clean up damage from winter and spring storms. Proper pruning will begin to restore most plants' natural shape.
Pest Control. Another benefit of summer tree pruning is pest control. By removing branches and fruit that have mites or aphid damage you are protecting the overall health and longevity of the tree. You are also ensuring that your fruit trees produce delicious, healthy fruit that's free of pests.
Wait till after the leaves fall. Mild fall weather may have you thinking about pruning shrubs and trees. But it's better to wait till late winter, or, at least, after leaves have fallen.
Differences Between Pruning and Trimming
Webb said pruning typically involves removing dead or diseased wood and thinning out stems and branches to improve the overall health and appearance of a plant. On the other hand, trimming typically involves cutting back plant material for reasons other than health concerns.
An improper cut like a flush cut (cutting too close to the trunk) or a stub cut (cutting too far from the trunk) can cause irreversible damage to a tree. A flush cut removes the branch collar and leaves a large wound in the side of the tree that won't heal properly.
In reality, pruning paint may impede healing and encourage the growth of rot organisms and insect infestation. Rather than seal out infection, wound dressings often seal in moisture and decay. In most cases, it is best to simply let wounds seal on their own.
July is the month for pruning fruit trees, especially well-established ones. A few simple, well-placed cuts can improve fruiting and limit the size of the tree, ensuring it stays compact enough for a small garden.
After a tree is topped, it grows back rapidly in an attempt to replace its missing leaves. Leaves are needed to manufacture food for the tree. Without new leaves, the tree will die. The new branches that sprout up below the cuts will continue to grow quickly until they reach the same size it was before it was topped.
Trees that Should Never be Trimmed During the Summer
This is because oak trees have a disease called Oak Wilt, which is spread by pests and could infect and even kill oak trees that are trimmed between April and October. Always wait until the fall and winter to trim oak trees.
The approximate thermal death threshold for trees in a temperate zone is 115°F depending on its age, thermal mass, water tissue content, and the ability of the species to adjust. Optimum growing conditions for most trees range from 70°F to 85°F. Overall tree temperatures usually run around air temperature (+ or - 4°F).
While it is possible to burn some types of freshly cut wood, any wood that is considered green that has not yet dried out or been seasoned should not be burned or should be avoided as much as possible.
During excessively cold temperatures
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.
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.
Never cut trees in dangerous weather conditions. Rain, wind, and lightning can all pose risk to your employees and affect the direction the tree falls. Make sure tools are in the proper working condition and appropriate for the job at hand.