Montana State University

Protect trees now to prevent severe winter damage

September 2, 2010 -- By Toby Day, MSU Extension horticulture specialist


MSU Extension horticulture specialist Toby Day advises that a few easy protective measures taken now can help prepare trees for winter and prevent harmful effects of cold weather. MSU photo by Kelly Gorham.   High-Res Available

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Tel: (406) 994-4571
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Throughout Montana, many trees including ash, cottonwood, maple, willow and even Colorado blue spruce have suffered moderate to severe winter damage due to the early and prolonged October freeze that we encountered last year. Some species, such as ash, have all but died, leaving just suckers growing from the base. In the case of Colorado blue spruce, many have just one or two branches that have died with more showing effects each month.

The extent of damage is somewhat determined by the species or variety of tree, while much of the damage can be traced to trees that weren't able to harden off, a term that describes a tree's tolerance in response to colder temperatures and shorter days. While sudden cold snaps like the one last October will always create some fall freeze damage to trees, we can help trees prepare for the cold with a few simple tips.

Withholding water and fertilizer and limiting heavy pruning in the fall will encourage trees to harden off properly. This includes evergreens, such as pine, fir and spruce. Heavy pruning and late fertilizer treatments encourage growth rather than hardening off, so restrain from fertilizing and pruning trees until spring. Throughout the month of September and into October, reduce and even stop watering trees unless they show signs of wilting. Once leaves turn color on deciduous trees and fall off, the trees (including evergreens) are in a dormant state. Once dormant, the trees will not respond to watering. However, after leaves have fallen, it is important to resume watering to saturate soil so that the trees have a water reserve for coming out of dormancy, which could be as early as the first week in January. Following leaf drop, water deeply once a week until the ground freezes.

While many parts of the state experience continual measured snowfall in winter, areas in drier regions may see trees that have suffered even more winter desiccation. Evergreen trees and shrubs show signs of extreme water loss to their needles and twigs following winter. Even though the ground may be frozen, it is a good practice to bring the hoses out periodically and water trees throughout the winter to supply the trees with water - especially during warm periods in winter when the Chinook winds blow.

Protecting newly planted trees from winter desiccation is important. Construct sun barriers for newly planted evergreens on the windward and south side of trees or shrubs to protect them from drying winds and intense reflective winter sun. Tying burlap between fence posts or even propping a wooden pallet on end usually does the trick. Deciduous trees with smooth and dark bark should have trunks wrapped with a tree wrap to reflect the sun, reducing sunscald to the bark.

To learn more about proper tree care, you can download a free MontGuide, a self-learning resource from Montana State University Extension, called "What's Wrong with This Tree?" at http://msuextension.org/publications/YardandGarden/MT199518AG.pdf or by picking up a free copy at your local MSU county or reservation Extension office.

Toby Day, (406) 994-6523 or toby.day@montana.edu