Cold weather does much more damage to trees than hot weather. Hot weather generally means less moisture which can be fixed by watering – at least for smaller trees. In addition most established trees have extensive root systems which can reach deep for water in case of extended drought conditions.
I would like to talk about three different types of cold weather in regards to trees. One is late spring frost, another is early autumn frost and the third is extreme winter cold.
The most common type of cold weather which damages trees is the late spring frost. Trees are highly variable as to when they start to leaf out or flower in the spring. If a tree is maybe marginal for your growing zone it may leaf out earlier than other trees and be susceptible to late frost. I have observed that if a tree is just starting to leaf out it may not have much damage from the frost. If that tree has fairly big/mature leaves it also may fair well. It is when the leaf is past the bud stage and not at the fully mature stage that frost will kill the leaves. This usually doesn’t kill the tree, but it does stunt the growth as the tree must start again growing new leaves.
Most trees flower in the early spring, it is just that very few trees have showy flowers. Like Oak trees – you don’t really see the flowers – but they are there and will produce acorns if the tree is mature enough. A hard frost in the late spring will kill those flowers and then no acorns. I have seen this more with Black Walnuts. Most years we see large crops of walnuts drop from the trees. But we have had a few years which almost no walnuts dropped, and they were years with a late frost. Of course if you are hoping for apples, plums, pears or other fruit a late frost also decimates those crops.
The second type of cold is one that I have only noticed a few times. Last year – the fall of 2020 we had extremely cold temps in mid-late October. According to the Rochester Minnesota airport on October 27th we had a low of 11 degrees the historical average low for that day is 33 degrees. A regular frost is something that young trees and still green leaves can handle. But last year we had temps down in the teens and the green leaves just turned brown and died (the cover photo of this post is of leaves which died because of that low temp). In addition many of the smaller 1 – 3 year old trees still had green trunks and hadn’t hardened off. The extreme cold killed the trunks and the trees had to start from the roots the next spring limiting their cumulative grow.
This extreme fall cold is something I don’t know much about. I also don’t know enough about the hardening off process which young trees go through to discuss. I have seen information about how tree tubes may extend the fall growing season and so postpone the hardening off process to the possible exposure to extreme fall cold.
The third cold I want to talk about is extreme winter cold. Many growers that sell tree seedlings indicate a maximum cold temp the tree can survive instead of the growing zone. I believe that extreme winter cold affects younger trees more than established trees. In January of 2019 we had a number of days with temps of 29 below zero or lower in rural areas which we live in. I had around 8 hybrid Black Walnuts which I purchased from Indiana in 2012 and were fast growing. All but the largest one died back to their roots because of that cold. Those walnuts are now growing back from the roots similar to the Chinkapin oak I have been writing about.
Well that’s what I know about the types of cold weather I have observed that have negatively impacted my trees.