February 16


What is Tree Dormancy?

By clientsite

February 16, 2017

What’s going on inside woody plants, trees and shrubs as winter approaches? The term “dormancy” is more than a simple or seasonal pause; it’s a series of physical and physiological changes. The process starts gradually in late summer and speeds up during autumn. Plants send energy to their roots and the fluid in their cells becomes super-cooled or saturated with solutes, similar to a type of antifreeze. Scales form over buds to protect them from freezing temperatures and drying out. Interestingly, woody plant roots do not enter full dormancy. Cooling conditions trigger a resting state, which can then be broken once conditions improve.

Last winter (’15/’16) proved to be a challenge for some of our trees. Remember the week of Christmas when the temperatures reached into the 60’s? During this warm up, trees began to break out of their dormancy, like they do in the spring, causing the trees’ natural “antifreeze” to subside making it vulnerable again to freezing temperatures. And of course, in true New England fashion, the temperatures dropped within a week into the single digits.

The Eastern White Pines took a hit that wasn’t noticeable until well into their growing season. The older needles, that were green coming out of the winter, started drying then browning and eventually died off within weeks of their decline. Although the new needles that budded were green and healthy, the trees were thinned and more likely to experience greater stress.

A White Pine in the spring after a mid-winter dormancy break. Notice the browning needles in the canopy.

Many Weeping Cherries, planted in the landscape, were also injured if not killed by the mid-winter dormancy break. The damage happened in the stem tissue killing off cells that move water and nutrients to other parts of the tree. These cells that were functioning started to decay as the season progressed. This resulted in stems that pushed out healthy leaves then died weeks later.

This Weeping Cherry finally succumbed to the freeze injury it sustained earlier in the year after a warm week in December.

As Certified Arborists, we make it a priority to protect plants against pathogens, insects, storm damage, etc. We promote preventative maintenance programs to avoid situations that affect the vitality of trees and shrubs, but unfortunately, when we are up against Mother Nature, it’s a bit more challenging. To help prevent damage from a mid-winter thaw and refreeze, we recommend thoroughly hydrating your trees and shrubs before going into winter to reduce the chances of drying injury associated with freezing temperatures.

When spring rolls around and your trees or shrubs aren’t looking their best, call ArborTech at (413) 525-0060 to schedule an appointment with one of our Certified Arborists or contact us here.


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