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Frost cracking, deep planting can affect the health of trees

November 15, 2018

Question: My father, who has sent you questions in the past, suggested I send you a picture of my maple tree. The two cracks in the trunk just appeared in the past week. I’m actually in Illinois, but our weather has been very similar to Pittsburgh where my parents live. This tree was transplanted approximately five years ago. I was curious if, with these splits in the trunk, whether or not I will lose the tree. The cracks are on the south and southwest side of the tree. Any input will be greatly appreciated.

Answer: Unfortunately, it looks very much like you are going to lose the tree. As evidenced by the photo you sent, the trunk is not just split, but the bark is also peeling completely off of the tree, which is far more concerning than the split in the trunk.

Tree trunks sometimes develop vertical cracks or splits (usually during the winter) due to something called “frost cracking.” Frost cracking occurs when the bright sun warms the bark and inner wood, and then is followed by a quick temperature drop at nightfall. This extreme temperature change can cause the inner wood and bark to split due to a sudden change of pressure within the tree’s tissues. It’s so sudden that, if you’re standing nearby, you may hear a “crack” or “pop” from the tree. Maples, cherries, walnuts, sycamores and apples are some of the most susceptible trees. It’s most common on the south- or west-facing side of young trees like yours.

However, while frost cracking can damage trees, more often than not, trees live for many years with frost cracks with no ill effects. Frost cracks cannot be prevented, and after the cracks occur, there’s little you can or should do to help them heal. In most cases, the cracks callous over, though sometimes they may serve as an entryway for fungal or disease organisms.

While you may think that the frost crack in your tree is its biggest cause for concern, I don’t believe that’s the case. If you look at how the trunk of the tree emerges from the soil, you’ll notice that it looks almost like a utility pole sticking straight out of the ground. But, if you look at a tree growing naturally in the woods, you’ll notice that the base of the tree flares out at ground level. The fact that your tree does not have an exposed root flare tells me that it was planted or mulched too deeply, which can cause decline and eventual death several years after the tree was planted (or transplanted, as the case may be).

The bark around the base of trees that are planted too deeply -- or around the base of trees that have mulch piled up against their trunk -- may eventually develop rot or be chewed away by voles or rabbits in the wintertime. When you plant or transplant a tree, always leave the root flare exposed and above ground level. And never pile mulch against the trunk of a tree. Make a “doughnut” of mulch around the tree; not a “volcano.”

Sadly, there isn’t much you can do for your tree at this point. If the bark were still intact, I’d suggest removing several inches of soil and mulch away from the tree’s base to expose the flare. Or, you could dig the tree out and replant it so that the flare sits above the soil level. But, at this point, I fear it’s too late for your tree.

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