NDSU Extension - Stark & Billings County

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Protect Your Trees from the Mower

The mower is one of the leading killers of trees in North Dakota

Mowers attack bark, the armor of a tree. Just beneath the bark is the phloem, a precious layer where nutrients are carried from the leaves to the roots. If you expose the bark, the phloem is destroyed. If you destroy the phloem, the roots stop receiving nutrients from leaves. The roots starve and die.

If that isn’t bad enough, the wounds created by mowers are easily invaded by diseases.
How much damage to the bark can a tree withstand?

Trees generally survive if the damage is limited to 25% or less of the bark around the tree. As damage levels increase higher, the tree suffers higher levels of decay and dieback. If the bark is stripped around the entire tree, it will die. This is called girdling.

If you love your trees, protect them against your terrorizing lawn mower (and string trimmer).

Place a ring of mulch around each tree. Follow the “3-3-3 rule”. Place a ring of mulch that is at least 3 feet in diameter around the tree—even more is better. The mulch should be 3 inches deep. Keep mulch to a minimum for the first 3 inches away from the trunk. Heaping mulch against the trunk can create stem rot and provide nesting habitat for voles.

Use wood-based mulches such as chips or shredded bark. This mulch will conserve moisture, smother weeds and enrich the soil. Wood mulch will insulate tree roots, keeping them cooler in summer and warmer in winter. Most importantly, the mulch will protect the tree from your mower!

Rock mulch is less desirable. It traps heat, accelerating bud break (and potential frost injury) in spring, as well as creating excessive heat stress in summer. Rock mulch compacts the soil and provides no nutrients.

Filed under: Trees
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