Pruning young trees - Column

Flower & Garden Magazine, Feb-March, 1993 by Monica Brandies

It took me 30 years to learn one of the basic principles of pruning: start guiding a tree's growth early. As the rules of tree care change, and once-accepted techniques for pruning are discarded, thank goodness that one rule still stands.

When I planted a seedling tree in front of our first apartment in 1958, a friend stood by and watched. "That first branch is pretty low," he said. "Do you think you want it there?"

Of course, I didn't want it 4 feet from the ground. I wanted the branching point to grow higher with the tree. But if I cut one branch off at that point it would remove half the tree and leave the other half lopsided. Moreover, it would make a scar on the trunk.

While I stammered and stuttered, my friend assured me, "It won't grow any higher. It will always branch at exactly that point. Watch and see."

The sapling was still too young to prune away what seemed like half the tree, I told myself, and I did nothing. It was a big mistake. I realize now that my friend was right, and I should have removed that branch.

The tree grew fast. Eventually we moved away, but I still drive past when I'm in the neighborhood. The tree is 40 feet tall now. The first branch is still 4 feet from the ground. Some day a heavy wind or snow is going to split it apart at that weak crotch, where I should have made the decision to prune when the tree was young.

Since then I have planted many trees. Some grow with a definite central leader and are gracious enough to shed their lower branches themselves. While they are still small and spindly, those branches seem little loss. The scars close over. By the time the tree is tall, the lower portion of the trunk looks, to the casual eye, like it always was branchless. Without any assistance from the pruning saw, these trees naturally assume a strong, graceful form.

Unfortunately, other trees tend to split into multiple trunks close to the ground. They are bound and determined to form a double leader, or even a triple. Trees sold at garden centers have often been spaced so closely in the nursery that all their branches reach straight upward.

So how in the world are we supposed to get one long tall trunk? And the first branch coming off at a wide angle, high up enough not to poke people in the eye or interfere with the lawn mower?

The answer is in annual prunings, usually performed in early spring before the tree leafs out, to gradually guide the tree into forming a strong framework of branches. Remove one or two of the lower branches each year until the lowest remaining branch is at an acceptable height. For most ornamental trees, this height should be at least 6 feet to allow people to walk beneath. Street trees should be pruned even higher; the scaffold of branches on fruit trees can be much lower to permit easy picking.

Since trees need leaves to make food for growing, don't cut off too many branches too soon. Sometimes it is necessary to keep lower branches, at least for a year or two, even if they are unsightly or imperfect. If too much of a tree's growth seems to be going into these lower branches, trim them back to encourage the central leader to reach upward.

Pruning doesn't end here. The need for selecting the best scaffold of strong branches as the tree grows is equally important. Large shade trees need a single central trunk with well-spaced, wide-angled branches. Don't wait too long to remove vertical branches that compete with the main leader. Pruning only gets harder the longer it is postponed.

When the tree gets tall enough to begin selecting branches for its permanent crown, watch the side branches and make sure they join the trunk at a wide angle. In general, crotches with narrow V shapes are weak. A raised ridge of bark forming in the crotch is another indication of weakness.

If the leader is lost in a storm while the tree is still young, select a flexible side branch near the top to take over the job. Stake or tie it into position until it grows into place.

Along with these specific guidelines for training young trees, several general pruning rules still apply: remove dead, broken or diseased branches; remove crowded growth or branches that cross and rub against each other; and remove water sprouts along the branches unless one is needed to train as a main branch. In addition, never "top" a shade tree, as the resulting stubs invite decay, and subsequent growth is spindly, weak and prone to insect attack.

For years we have heard that cuts made to remove branches should be as nearly flush with the trunk as possible. In the last few years a new philosophy has gained acceptance.

Around the base of every branch is a "collar." Sometimes this is an evident ridge in the wood; other times it is a less obvious swelling. Arborists have found that when they make the pruning cut just beyond the branch collar, leaving it intact, the pruning wound starts to heal more rapidly. The roll of callus growth around the wound area soon seals it off. Pruning to leave the branch collar often means making the cut at a completely different angle than would be made for a flush cut. It also results in a smaller wound.