You should not do aggressive pruning in summer. Major structural pruning should wait until the plant is dormant in winter. Improper pruning will stress the plant. You might cut off valuable buds.
Late summer or early fall pruning causes vigorous re-growth of tissue, which in some cases may not harden off by the time winter arrives, leading to possible cold damage to the new growth.
A summertime shape up is healthy for people and trees alike. Although the best time to prune any plant is typically in its dormant phase, trees will benefit from a nice mid-season trim as well. Summer trims can cut down on the amount of pruning you'd have to do later in the year.
Helps Control Disease
Some trees, like oaks, should only be pruned during the dormant season because they are especially susceptible to oak wilt disease, which is known to spread extremely fast in the spring and summer.
"They heal much better when we prune in the heat. They do recover quicker," says McCue, a master gardener for 10 years.
Wait until just after any fruiting and flowering is complete to cut back. Prune a tree or shrub that produces fruit or flowers too early, and you'll cut off fruit and flowers. Prune the shrub or tree too late, and you may cut off growth that would have produced fruit and flowers next year.
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.
In summer, leaves engage in photosynthesis and produce carbohydrates. The tree translocates those carbohydrates throughout to grow roots, shoots, leaves, and fruit. By removing leaves during summer pruning you remove a resource point and thus reduce energy for overall tree growth or regrowth.
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.
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.
Few plants are pruned this time of year because pruning encourages new growth that does not have time to harden off before winter. Late-season pruning typically does more harm than good.
Pruning during the growing season always stimulates new growth. During summer's heat, having to produce that ill-timed new flush of growth greatly stresses a tree. Pruning in the fall is even worse as it prevents the tree from going into a natural dormancy. The exception is heavily damaged, disease or dead wood.
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.
In general, avoid pruning landscape trees in mid- to late summer (July, August and September), unless it's very light, because you can induce an off-season growth spurt, which can leave some species, such as ficus, vulnerable to freeze damage.
Pruning in August improves plant form just ahead of fall's growth spurt. Light shaping now will look beautiful after new fall growth arrives in the weeks ahead. Note: Plants should be well watered in the days ahead of pruning. Those that are experiencing drought stress should not be pruned.
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.
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.
Don't Prune in Late Summer and Fall
Pruning shrubs in August or early September may encourage a late flush of growth.
Dormant Pruning Avoids Spreading Disease
During winter, the bacteria, fungi, parasites, and insects that cause and/or spread disease are either dead or dormant. As a result, diseases are less likely to be transmitted by winter pruning.
Leaves the crown open to wind damage and sun scald, and. Increases reaction, or stress-response, growth sprouts (“watersprouts”) along the trunk and branches. These reaction sprouts are a sign of over-pruning – the tree is putting out new growth quickly in an attempt to generate energy through photosynthesis.
“Root pruning does not stimulate root branching all the way back to the trunk. Roots are often pruned before moving a tree in hopes of creating a denser root ball. However most root growth after root pruning occurs at the end of the root just behind the root pruning cut, not back toward the trunk.
Cut too much and you'll risk nutritional deficiencies or branches that are too weak to tolerate the wind or fend off diseases or insect invasions. Over pruning and topping can permanently disfigure your trees, or even kill them. Further, a tree's foliage is important for protecting it against excessive sun exposure.
Prune shrubs that flower before mid-June after they flower. For these spring-blooming beauties, remove the largest stems, cutting them back to the ground. This causes the plant to push out new growth from both the crown and all remaining stems.
Boxwoods can be pruned any time but late summer and early fall.