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Wrapping trees in fall can be lifesaving

Gardening columnist Don Kinzler recommends wrapping the trunks of young trees each fall to prevent winter injury and animal damage.

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Garden centers sell several options for wrapping tree trunks.
David Samson/The Forum
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According to a proverb attributed to ancient Greece, “A society grows great when old men plant trees in whose shade they know they will never sit.”

The proverb is a favorite of mine, not just because I like trees, but because the simple words say much about initiating good things, even though others might be the recipient instead of us. Planting trees expresses faith in the future.

When any of us plant young trees, there’s usually one goal in mind – doing our best to ensure the trees live to a ripe old age. A simple, but important step, is wrapping the trunks of young trees each fall.

Tree wrap is used to protect young and thin-barked trees during the winter months. Wrapping trees helps protect against sunscald and frost cracks, and both are temperature related.

Sunscald is an injury to tree trunks that usually occurs on the south or southwest side of the tree. During winter, those sides are warmest. On sunny winter days, the sun’s rays heat up the bark, causing dormant cells beneath the bark to become active. Just like a skier getting sunburn from the sun reflecting off winter snow, tree bark likewise absorbs the sun’s rays.

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When the sun sets, the trunk cools rapidly, and the activated cells freeze and burst, injuring the trunk’s tissue. Thin-barked trees are most susceptible, and types most affected include maple, linden, mountain ash, honeylocust, plum, cherry, ornamental crabapple, and apple.

Frost cracks are another temperature-related disorder, causing vertical cracks in the trunks of trees. As with sunscald, sun warms trunk cells, causing them to activate and expand. As the sun sets, the outer bark temperature cools quickly, but the inside of the tree remains slightly warmer, which results in splitting of the wood. Younger trees are most susceptible, and it seems especially problematic in maples.

To prevent both sunscald and frost cracks, young trees, especially the types most sensitive, and smooth, thin-barked trees, benefit from protective tree wraps their first five years. Smooth-barked fruit trees can benefit even longer.

Wrapping the trunk reflects the sun’s rays off the bark, keeping it cool, and preventing the damaging effects of freezing and thawing. For best results, the wrapping should extend around the trunk from ground level up through the first major branches.

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Wrapping tree trunks can save their lives by preventing winter injury and animal damage.
David Samson/The Forum

Several types of tree wraps are available. White plastic tube-like tree guards are commonly sold with new trees, or they can be purchased. Many garden centers also sell rolls of tree wrap material.

When using rolled wrap, begin at the tree’s base, fasten the wrapping to itself with tape, spiraling it upward, overlapping the material until you’ve intertwined the wrapping through the lowest branches. Rolled wrapping makes it easier to wrap and protect higher on the trunk, because it can weave between branches.

Winding tube-type tree guards around the trunk where major branches emerge can be a challenge. Black tree guards shouldn’t be used because they absorb heat, which is the opposite of what’s needed.

Tree wraps should be applied each year in early November and removed in April. The wraps should not be left on year-round because they can harbor insects and moisture-related rot diseases. If tree guards or wraps are left intact for multiple years, they can easily become embedded in the trunk, causing irreversible damage.

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As an added bonus, tree wraps or guards can protect against wildlife damage. Rabbits, deer and rodents can destroy young trees, either by gnawing bark and main branches, or by rubbing away the trunk’s bark.

Apple trees, the region’s most commonly planted fruit, are especially vulnerable to winter injury from sunscald, frost cracks and wildlife. As long as the trunks remain smooth, even older apple trees are easily injured. In addition to trunk wraps, fencing with chicken wire or metal hardware cloth will provide greater protect against wildlife, if extended high enough so it doesn’t become overtopped by snowdrifts.

More gardening columns from Don Kinzler

Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at donald.kinzler@ndsu.edu.
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