How to prune trees

There are two main reasons to prune a tree: To enhance its health and vigor or to make it grow the way you want. Some specific benefits of both approaches:

Reduce crowding

Trees such as crabapple develop dense crowns over time. Removing some of the twiggy growth crowding the tree's interior allows more sunlight to enter and air to circulate, reducing the chance of disease and pests. The new growth after pruning is also more disease-resistant. Many trees sometimes produce two branches that grow in the same direction and compete for the same space. In that case, you'll want to remove the less esthetic or robust branch to provide room for the other to flourish.

Repair or prevent damage and ensure safety

Broken, ragged branches are vulnerable to various insects and diseases. Branches that are dying, dead, or diseased should also be removed as soon as possible to prevent the disease from spreading and the branch from falling on its own. Trees growing over your house or other structures should be inspected annually for signs of decay so that threatening limbs can be removed.

Manage wayward growth

Any tree can occasionally produce branches that brush against the house, hang too low over a pathway, or block the view from a window.

Increase or improve flowers or fruit

Proper pruning can dramatically increase the quality and quantity of flowers or fruits a tree produces. Pruning a crape myrtle (Lagerstroemia) in later winter will produce more flowers in summer, for example.

When to prune

Light pruning—removing dead or broken branches—is safely done any time of year. But some times are better than others for different needs.

To invigorate a tree

Late-winter or early spring pruning is best for most trees, since it allows the tree to concentrate its stored energy on fewer branches. This leafless time also eases pruning by reducing cleanup and letting you see the tree's shape. Regrowth covers the pruning shortly, and pruning wounds quickly begins healing. Late winter and early spring are also when to prune trees that flower in summer, such as crape myrtle (Lagerstroemia), to encourage vigorous growth that produces summer flowers.

To retard growth

Late-spring or early summer pruning is best for slowing the growth of fast-growing trees. Summer pruning also tends to reduce the number of suckers that sometimes grow around pruning cuts. Prune trees that tend to ooze or bleed after pruning during the warm temperatures of summer. These include birches (Betula), dogwood (Cornus), maples (Acer), and walnuts (Juglans).

Hint

In hot-summer areas, avoid removing too much foliage from trees with thin bark, which can become sunburned.

How to prune

Pruning is easy and requires nothing more than a pair of pruning shears to get started. But pruning to solve or prevent problems, to make a tree attractive or productive, or to minimize future work takes a bit of understanding and thought.

Thinning

This is how to prune most trees. The word invites confusion because it refers to both a pruning cut and a desired result. A thinning-type pruning cut means to remove a branch either at its origin or to an adjoining branch. Doing so encourages subsequent growth to follow the tree's natural branching pattern. Thinning also means selectively removing branches to allow light and wind to penetrate the tree.

Thinning large limbs vs. Thinning small limbs

Heading or topping

This method of pruning is rarely desirable. Cutting to shorten a branch or stem at an essentially random point is a heading cut. Heading cuts stimulate growth to occur just below the cut, usually clustered together. Heading large branches of mature trees produces vigorous, twiggy growth that ruins the natural shape.

Hedge-shearing refers to multiple heading cuts on small branches. A hedge's thin exterior layer of leaves and leafless, twiggy interior is typical of the growth produced.

Heading a tree means cutting a branch at an essentially random place. Subsequent growth is clustered near the cut.

Removing heavy branches

Ripped bark caused by pruning off a heavy branch is a common cause of long-term damage. Prevent this by removing most of the weight from the branch first, several inches out from the final cut. Called a three-saw cut, this is the only way to safely remove any branch that may tear bark.

1. Cut up from the bottom about a foot farther out from the location of the final cut. Cut about a third of the way through the branch or until the saw begins to bind.
2. Cut down from the top an inch or two farther out on the branch. Once you've cut about half way through the branch, its weight will force it to break at the point of the bottom cut, and the branch will fall off.
3. Remove the remaining stub. Don't cut flush with the main trunk; that would create an unnecessarily large wound. Cut from the top or bottom just beyond the place where the branch and trunk join, called the branch collar, which is often indicated with prominent ridges of bark.