Tree trimming, also called pruning, is a way of directing a tree's growth by removing twigs, branches or large limbs. Done properly, it can give a tree a more beautiful shape and a stronger framework. If, however, cuts are made at random, they can destroy the shape of the tree. All cuts must have clean edges so they can heal quickly and must be made close to a branch or bud so there is no stub left to rot.
Shaping A Young Tree
If at all possible, avoid taking off large limbs by slowly shaping a tree from its first years in your garden. The wounds will heal more quickly and the tree will put all its energy into a framework of trunk and branches that will last.
Choose the largest branches, spaced evenly around the trunk at about a foot to a foot and a half intervals, and remove weak branches or duplicates at about the same height. You may not want the lowest branches five years from now, but leave them until the upper ones grow in. Wait until the second year for your major pruning, allowing the branches to feed the growing root system the first season.
Thinning Congested Branches
Some trees sprout a multitude of small branches near the trunk, creating a thicket of weak growth. To get a strong shape, remove all unnecessary growth, leaving only large limbs at the center, smaller ones farther out and twiggy growth at the tips. This gives a silhouette that matches the common image of a tree rather than the dense mass of growth we call a shrub.
Raising The Canopy
As a tree grows taller, the lower limbs will often need to be removed to keep the tree-shaped silhouette, as well as to allow greater head room for walking underneath. Take a few branches off the bottom each year and also remove some of the side branches from the main framework, opening out the center.
As you open out the center, the tree becomes less resistant to the wind, less prone to breaking off limbs or toppling over all together. Topping a tree to reduce wind resistance is less effective and often destroys the shape of the tree.
Removing Weak Or Diseased Wood
Any branches that show signs of disease should be removed immediately to prevent infection of healthy growth. Any thin, spindly growth should also be removed.
Reducing The Size Of A Tree
Sometimes a tree just wasn't planted in the right spot and, after 10 or 20 years, outgrows the space it was given. If possible, remove the longest and tallest branches right down to their base, leaving the shorter ones unchanged. Otherwise, cut these branches back to a side branch well beneath the outer edges of the canopy, where the cuts will be hidden by the shorter branches.