Ask the Arborist

Q. When is the best time to prune a young tree, and how many branches should I remove? Is there anything I should do to protect the tree where branches were removed?

A. The best time of the year to prune young trees depends upon the species of the tree, but here are a few basic guidelines.

If you are just trimming out dead branches, do it when the tree is fully leafed out so you can easily differentiate live wood from dead. Pine trees should always be trimmed in the cool months between October and April.

If you are trimming a fruit tree, do it before the new growth begins in the spring so you don't interfere with blossoming and fruit production.

Generally speaking, though, almost any tree can be lightly trimmed almost any time of the year.

The three main reasons to trim a tree are safety, health and aesthetics. With a young tree, you wouldn't think the safety aspect would be a factor. But much of the pruning done to a tree when it's young plays a role in some way when the tree matures.

We've all seen examples of bad trimming. It's that tree that looks like a telephone pole with five stubs sticking out of it. I call that the first phase of tree removal. Not only does a whacked tree look bad but it's also detrimental to the health of the tree.

Never start pruning a tree just for the sake of lopping off branches or cutting off the top. When in doubt, sit down and take a long look at the tree. If you can't think of a good reason to trim it, using safety, health or aesthetics as your guide, then don't.

Always keep one thing in mind: Trees make their own food using their leaves as little sugar factories. The more leaves a tree has, the more food it's producing and the healthier it can be.

When trimming a young tree, your goal should always be to train it into a structure that has a good strong main stem (trunk) and well-spaced branches.

Leave as many branches as you can on the lower part of the main stem because they contribute to its strength. As the main stem gets stronger in a few years, you can then trim off the extra branches if you want to. If there are two main stems competing for dominance, pick the best one and trim the other one off.

Prune out competing branches and any branches that look weak. Always trim to a lateral branch or other growing point and don't leave unsightly stubs. Each pruning cut should be carefully selected and correctly made using sharp tools. And remember, when all else fails, use common sense.

The necessity of protecting the open cut area where branches are trimmed off has been debated by experts. Many products on the market can be applied to pruning cuts. Some are paint-based sprays; others are as thick as tar and must be applied with a putty knife.

The bottom line, though: It just isn't necessary to seal a pruning cut.

A young, healthy tree will begin the healing process almost immediately, creating a callus or woundwood that will completely heal over and close off the cut. My advice to you is to make good clean pruning cuts with sharp tools and then leave the tree alone.

David D. Mortimer is a certified arborist with more than 30 years' experience in the treecare industry. Email questions to dmortimer@theacorn.com.

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