Tree care: Late winter is prime time for pruning

Pity the poor trees.

They shade our homes, add glorious color in the fall, give us apples and cherries and provide beauty year-round. Yet, although many of us think we look at our trees all the time, do we really see what's going on with them?

Now's the ideal time to take a closer look at trees, and prune them to correct problems. In late winter, there are no leaves to hide crossed and rubbing branches, splintered wood and other issues. An expert certified arborist can see how a tree's entire canopy looks, and prune for the health of the tree, as well as for your safety.

Late winter also is the time when it's easiest for trees to recover from pruning. Wounds from late-winter cuts will heal quickly when spring comes, even in trees like maples and birches that bleed sap. And at this time of year, most tree diseases and pathogens are not yet active, so chances of spreading those problems while pruning are minimized.

But our climate is changing. Warmer weather is arriving sooner in Minnesota than in the past. The University of Minnesota Extension Service recently released a fact sheet suggesting that homeowners move quickly to cut out tree cankers and galls before the weather warms. Some of those pathogens begin to reproduce and spread when temperatures are just above freezing.

Among those diseases is black knot, a serious problem on plums and cherries that can kill young trees. Black knot's knobby, swollen masses are easily spotted on branches at this time of year.

Crabapple and apple trees, pagoda dogwoods, mountain ash and honey locust can all develop cankers, some of which look like sunken dead or gooey spots on branches. Stressed trees that were improperly planted or not cared for are especially prone to cankers, so it's hard to eliminate the damage once it begins, especially if the canker is on the trunk.

Here's a link to the U's bulletin on this issue: http://tinyurl.com/jhat3cr

Now is also the time to prune for our own safety and convenience. While it's best to shape trees when they're young, most of us plant a tree and then forget about it. Tired of crouching to mow under that crabapple? Sick of that maple branch scratching the car as you drive up to the house? Now's the time for some judicious pruning.

It's no exaggeration to say that pruning is an art, so if you're going to tackle trimming a tree, do it correctly. Improper pruning prevents trees from healing themselves and can result in serious problems later. No more than a quarter to a third of a tree's canopy should be removed at one time, and trees should never be given a mindless haircut to reduce height. That practice, called topping, results in weak, spindly "witches broom" growth.

So unless you're willing to learn a bit about pruning (a good guide is at http://tinyurl.com/zy6jbwu) and have a relatively small tree to test your new skills on, it's best to hire an expert to trim a tree. Pruning a large, mature tree is not only a skill, it's a dangerous job unless you know what you're doing. That means you don't hire the uninsured guys who cruise neighborhoods in pickups, chain saw in hand, to prune trees at bargain prices.

Instead, look for a certified arborist who has training, experience and references and can offer proof of insurance. Such work isn't cheap; get several estimates. But it's worth investing in the health of trees. Studies show the benefits of mature trees include cutting air-conditioning costs, helping the environment and increasing your property values.