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A December to Remember!

Brutal winter weather decimates trees.

By Chris Leinster - January 1, 2023

Happy New Year! As we kiss 2022 goodbye, let's bid last December good riddance. Our Colorado Climate is brutal on trees, and December gave us a stark reminder why most trees don't grow here. In fact, without human interference, most trees can't grow here at all. Fortunately, with a little knowledge and a bit of effort, many of our favorite trees from similar climates around the world can thrive for generations to come, but last December may have been damaging or fatal to many of our leafy friends.

The month started mildly enough, with temperatures comfortably in the 50s and even poking above 60 on a couple of occasions. Then on December 21st, the temperature plummeted from a balmy 51 degrees to 24 below zero overnight! This marked a 75 degree drop in temperature in just a matter of hours. How wildlife and livestock survive such a rapid shock is beyond me. It's remarkable that trees and plants can withstand such whiplash. Unfortunately, some won't.

The most catastrophic consequence of such dramatic temperature declines is frost cracking. This occurs when water within the tissue in the trunks of the trees freezes. Water expands as it freezes, and rapidly freezing water within trees can split the bark and rupture the heartwood. Have you ever tried to chill a bottle of beer in the freezer and forget to take it out? You likely encountered a shattered bottle, as water in the beer expanded and cracked the glass. The same phenomenon can occur in trees. Trees have defenses to counter cold temperatures, but this historic event is sure to have wreaked havoc on trees all over town.

There's really nothing that we can do to try to mitigate this. We winter wrap trees to protect from the sun, but there is really no practical way to prevent trees from freezing. Most seasons the trees own strategies can protect them from winters' wrath. December's nearly unprecedented drop will test even the hardiest of trees.

Just as we were beginning to thaw out, even reaching 62 degrees on 12/27, the bottom abruptly dropped out and a ferocious snowstorm dropped almost a foot of heavy, wet snow over much of the Denver region Wednesday the 28th. Snow accumulated at the rate of several inches per hour. In fact, by the time I finished shoveling my driveway I turned around to find almost 2 inches piled up where I had started!

Snow has an insulating effect and can actually protect the trees from freezing temperatures. The moisture it brings is of course welcome as well. The problem with rapidly accumulating heavy wet snow is the weight. Snow loads up on branches and boughs, bending them to the ground, and inevitably breaking some. Snows of this magnitude can clobber newly planted trees and can even rip mature trees completely apart.

This is why winter tying of trees, particularly upright evergreens like Juniper and Columnar Spruce, and multi-stemmed trees like Serviceberry and Canada Red Cherry, is essential along Colorado's front range. It's also wise to run out during a snowstorm to gently brush or knock the snow off your trees. Check out my prior blog on tree tying and even link to a poorly made video detailing how its done

Unfortunately, Happy Trees cannot warranty against physical damage as a result of unprecedented freezing or snow load. I'm not looking forward to the many uncomfortable conversations I'm predicting for this upcoming spring, as homeowners venture back outside and some discover fatal damage to recently planted trees. Happy Trees guarantees that trees are healthy at the time of purchase, and that trees were properly handled and planted. Even if we did everything perfectly, there's nothing we could have done to prevent frost cracking or storm damage. We wouldn't warranty your tree if it was hit by a car. Last December was more like a runaway freight train!

I don't mean to sound overly pessimistic. As I walk the grounds of the Westminster Arboretum and the world headquarters of Happy Trees, I observe no evidence of frost cracking and only minimal damage from snow load. Still, a quick drive around the neighborhood reveals major damage to an unfortunate few mature trees. Winter is the bane of Colorado gardeners, only cherished by skiers and arborists.