Are trees exploding in the cold?

The recent cold temperatures have led to online posts claiming that trees are exploding from the cold. Emily Swihart, Horticulture Educator with the University of Illinois Extension, spoke with Our Quad Cities News via Zoom to set the record straight on "exploding trees."

She said people don't need to worry about their trees going to pieces. "I think we're hearing about exploding trees in part because it's an attention-grabbing title. 'Exploding' might be an exaggeration of what is actually happening, but trees can be affected by the cold temperatures. Since we had a dramatic drop in cold temperatures lately, I think the combination of an exciting idea of trees exploding and really cold temperatures developed a media frenzy, if you will."

"I think most of the time when we're talking about exploding trees, we're actually talking about a pretty common issue that we can see on trees from winter to winter, which is called frost cracking. It can make a noise when it happens, in some cases. You have to be outside near a tree to hear that happen and you have to be there right at the right time, so most of us won't hear that sound, even if our trees do have a frost crack in them."

What causes the cracks? "The dark tree bark is going to warm under sunlight and in warmer day temperatures, so it'll warm and it will expand," Swihart said. "If that temperature and if that expansion happens underneath the bark at nighttime, when the trees are going to be cooling off under nighttime temperatures, sometimes that outer material, the bark, can contract so much and at a faster rate than the interior of the tree, that it can cause tension. There can be pressure built up and that can cause a crack or a fissure in the bark."

Swihart says frost cracks can happen during a typical winter, but the recent extreme temperatures have made the chances higher. "Some species are more susceptible to it than others, and so it has to be a combination of the right conditions. Something that can contribute to frost cracking is a dramatic change in temperatures. If trees have not become acclimated to a temperature, let's say we have really cold temperatures early in the winter. In December, trees may not have had enough time to concentrate sugars, to dehydrate, to become acclimated to our winter temperatures, so that can cause a higher prevalence of cross cracking."

"Thin bark trees are at more risk for cracking, like maples or birches. Their bark is just naturally thinner, so it is more susceptible to that pressure. Younger trees, even if they develop thicker bark as they mature, when they are younger, they have a thinner bark, so they're more susceptible. You're going to see it more on the south or southwest side of a tree, because that's where the sun is going to warm the bark more during the day and then it's going to cause a greater difference between the temperatures of daytime and nighttime temperatures."

Fortunately, Swihart says there are ways to help trees survive winters. "A healthy tree is going to be able to acclimate to winter temperatures and withstand winter better. So, we want to hydrate our trees going into the winter. Most people don't think of watering our trees, especially our young trees, in the fall, but we want to make sure that they are well hydrated. If we've had a dry summer and a dry fall, watering, putting a hose on the roots of that tree and watering it so that it can hydrate is going to help."

"Wrapping our trees, we can do that. There's some caveats that I want to make sure that everyone understands. We want to use a white wrap on those trees, because white is going to reflect the light and resist warming up more than a darker color wrap. We also want to make sure that we remove that wrap in the spring, we don't want to leave that on all year long." She said there isn't much homeowners can do to protect their trees from cracking, but there are ways to help. "It's generally not fatal to trees, but there's also nothing we should do to help, like seal the wound or cover it up. A tree is going to respond in its own way. We want to support the health and vigor of those trees by watering it, by pruning properly, by mulching, by keeping animals away from the trunk of the tree with those wraps in future years."

"We don't need to worry about taking it out of the landscape right away, but we do want to monitor it. We want to make sure that we're watering it, we're mulching around the base of the tree, we're not injuring it with mowers or string trimmers. That is a wound that we don't want to add to the tree ever, but especially if the tree is stressed from a frost crack."

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