Trimming helps boost the proper growth of a tree, as the extra branches and overgrowth can prevent trees from getting their necessary moisture and nutrients. On the other hand, the purpose of pruning is to remove infected, diseased, or dead branches of a tree.
Tree pruning involves the removal of live branches, as well as dead, diseased, and damaged branches for the health of the tree, while tree trimming only involves the removal of branches that interfere in some way.
The ISA guide to tree trimming (they use the term “pruning”) covers the basics of how to properly maintain mature trees.
Pruning is used to remove unnecessary branches. Trimming, on the other hand, promotes healthy growth. Both services are performed at separate times of the year, using vastly different pieces of equipment, to provide a better aesthetic and healthier landscape. Understanding the difference, though, is crucial.
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.
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.
The answer is: do not trim your trees in the fall! Trimmed trees may look neater to you, but dead or diseased trees are not very neat at all, and that's what you are risking by cutting back trees that are slipping into dormancy. Pruning trees stimulates them to produce new growth – it's meant to.
The 1/3 rule involves cutting about 1/3 of wood during any pruning activity. This moderate pruning practice is a balanced approach to thinning out shrubs to stimulate new growth. The plant loses a good amount of stems, usually on the top section, allowing more light and air to enter the inside of the plant.
In pruning, there are three primary types of pruning cuts, thinning cuts, reduction cuts, and heading cuts, each giving different results in growth and appearance.
Proper pruning encourages strong growth, increases flower and fruit production, improves plant health, and removes damaged limbs, all which give aesthetic appeal to a tree. Pruning at the right time and in the right way is critical, since it is possible to kill a healthy tree through neglect or over-pruning.
The two basic types of pruning cuts are heading and thinning. Thinning cuts are the least invigorating type of cut and are the most effective pruning cut for maintaining woody plants in their natural form. Pruning, particularly heading cuts, stimulates regrowth very close to the pruning cut.
It increases the level of carbon dioxide in the atmosphere. Ground water level also gets lowered. Deforestation disturbs the balance in nature. If cutting of trees continues, rainfall and the fertility of the soil will decrease.
Can tree branches grow back? When pruned properly, removed tree branches will not grow back. Instead, the tree will grow what looks like a callous over the pruning cut, which helps protect the tree from decay and infection. Because trees heal all on their own, you don't have to use a pruning sealer!
Over pruning reduces the foliage needed to make food for the tree, so in effect, it starves it. When a tree has been over pruned, you may not see much new growth during the spring. In the winter, more branches than usual will break as a result of heavy loads.
The best rule of thumb to use when making pruning decisions is to know that you can safely remove up to one-third of the plant's growth at any one time.
RULE 1: Prune your block with the weakest trees first and your strongest trees last. Trees that are pruned in early winter become more vigorous than trees that have been pruned just before or after flowering.
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.
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.
If a tree repeatedly loses too much of its canopy at one time, it can become weak or even die from the stress. That's why you shouldn't trim more than 25% of a tree's canopy at one time. Cutting the branch collar can also be a nasty error.
If your tree has a less severe problem, one of the best times to remove trees is during the dormant season, between late winter and early spring. Here's why. Dormant trees are leafless and lighter, so it's much easier for a certified arborist to cut and handle the branches.
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.