Winter Pruning Can Improve Health and Value of Trees

First posted on 03-09-2010

The dead of winter might not seem like an opportune time to trim trees, but that’s exactly when you should consider improving your trees.

University of Missouri faculty took time recently to explain how and why tree farmers and enthusiasts should be sharpening their saws and pruning now.

“The best time to prune is when nothing is growing, so try to prune from Martin Luther King Day through March,” said Mark Coggeshall, a research analyst with the MU Center for Agroforestry, at a Feb. 27 workshop at the MU Forage Systems Research Center in Linneus.

“Avoid cutting on your trees in April and May at all costs,” he said. “Once temperatures start warming up the tree’s sap really starts flowing, and you don’t want to cut when it will make the sap ooze out of those cuts.”

As he stood ankle-deep in snow, Coggeshall practiced what he preached. Wielding his pruning shears, he selected limbs in a four-year-old stand of black walnuts.

“Approach it like you’re a barber: Take a little off and stand back to see the effect,” he said. “You can’t be ruthless. In any given year try to take off the biggest branches, but keep in mind that you don’t want to remove more than a quarter of the leafing area.”

Coggeshall said pruning should begin at the top of the tree and move downward, leaving limbs in a helix pattern as you revolve around the tree. A rule of thumb is to remove a limb if it’s opposite a more dominant branch that’s larger in diameter or competing with the terminal bud in the top of the tree.

Limbs ideally should be cut when their base is less than 2 inches in diameter. Cut above the limb collar - an area at the limb base that’s designated by a slight swelling next to the main tree stalk. That collar will heal the wound caused by the cut limbs.

Pruning early in a tree’s life can help establish straight timber - a value-adding asset when selecting trees for harvest later. Tree limbs naturally push away from each other, so crowding causes limbs to diverge from a tree’s vertical axis. This can make the tree less straight and cause structural weakness later as side limbs compete for dominance.

“In the black walnut business, you’ve got to manipulate and train the tree to get a straight piece of timber, and sometimes you can’t salvage a tree with terrible genetics,” Coggeshall said. “In that case you can coppice it (cut it off at the base) and a new shoot will often grow like a corn plant off that established root system.”

For improving established woodland, MU Extension forester Hank Stelzer said the best approach is to nurture the best trees and forget about the rest.

“Get in mind your ideal tree and what you’d like to see on your property, whether it’s for lumber or wildlife, and focus on the gems you can find,” Stelzer said.

Stelzer said that eliminating surrounding trees, leaving about 10 feet of clear sky between the “gem” and neighboring trees, will leave more nutrients and canopy space for the crop tree.

“If it seems like too much to do with your entire acreage of woods, I suggest you concentrate on three to four acres every year to improve your forest’s health,” he said. “This is a good way to start looking at your woods.”

Photo: Mark Coggeshall, MU forestry research analyst, shows the proper way to prune black walnut trees at the Forage Systems Research Center in Linneus on Feb. 27.
Photo credit: Roger Meissen/MU Cooperative Media Group