Question: My trees make all kinds of popping and cracking sounds during really cold winter weather. What’s all that racket??
When temperatures dip well below zero, trees will make all kinds of popping and cracking noises, especially if the temperature drops very quickly. These sounds are typically caused by frost cracks.
What is a Frost Crack?
When water freezes, it expands in volume. The sap in trees is made of water diluted with carbohydrates (sugars) and minerals, which acts like antifreeze. The higher the sugar content, the lower the freezing point of sap.
But there is always a point where even sugar-rich sap will freeze. Depending on how much sap is in the tree, its sugar content, and the temperature, it can result in a vertical cracking in the trunk, called a frost crack.
Frost cracks also form when the temperatures heat up. On sunny winter days, tree bark will warm from solar energy. This causes cells to expand in the bark and the sapwood under the bark. When the sun goes down, the temperature drops very quickly causing the bark to contract. However, the sapwood under the bark doesn’t cool as fast, causing the bark to crack.
Since sun exposure can be a key driver, the south and southwestern side of trees are where you will see many of these cracks.
Effects of Frost Cracks on Tree Health
Trees are similar to the plumbing in your house; they have xylem and phloem tubes in the interior of the tree, which transport fluids up and down the tree. When the sap freezes, these tubes burst just like the copper pipes in a house.
Frost cracks can be small and internal (so you don’t see them) or large and external (so they break through the bark). These larger frost cracks are the ones you usually hear – they tend to make that loud crack or pop that wakes you up in the middle of the night. Some cracks can be severe enough that they crack almost anytime the temperature plunges, year after year.
During the spring, the tree will try to grow over the crack with a special type of wood called “reaction wood” (kind of like a scab). Unfortunately, in most cases it cracks again the next winter.
This cycle of annual cracking and reaction wood growth leaves a large vertical seam, which is an indicator of a weak tree that, in many cases, has compromised strength and internal decay.
So while popping sounds don’t mean that your tree is going to fall down any time soon, take a good look at your trees in spring to see if there are any vertical seams. Keep an eye on them from year to year and if you have any concerns, call in an arborist for a hazardous tree assessment.
