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The Best Way to Mulch Around Trees

Author:Terry Baldwin
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squirrel staring down tree trunk
Photo by Kylli Kittus on Unsplash

Planting new trees takes a lot of labor and often a lot of cash. Mulching them greatly improves their chances of long-term survival. But improperly applied mulch can cause trees to die prematurely. To learn why and how you should mulch trees, read on. The neighborhood squirrels and birds are counting on you.

Why mulch is good for trees

Research has shown that mulching trees "can almost double" their growth rate, according to Kansas State University Extension. Here's why:

  • Mulch conserves moisture and moderates soil temperatures.
  • It keeps grass from hogging the food and water.
  • Mulch acts like a bodyguard, keeping lawn mowers and weed whackers a safe distance from your tree.

This last point is the most important. The larger the amount of bark removed from a tree's circumference, the greater chance it will die. Completely stripping a band of bark from around a tree "will certainly kill it," according to Dr. Curtis Smith, horticulturist with the University of New Mexico Extension.

Tissue underneath bark carries food from leaves to roots. No food? Roots die. Dead roots? Leaves die. And the tree slowly expires. So keep lawn machines away from tree trunks.

dead tree with stripped bark
The bark has been almost completely stripped from the base of this tree. A mulch bodyguard might've saved it from an early death.

The worst way to mulch trees—the volcano

tree with mulch volcano
Don’t mulch your tree like this – it’s piled too high over the root ball!

Piling mulch around the tree trunk in a volcano shape invites problems:

  • Surface-feeding tree roots will establish themselves in the mulch volcano instead of spreading out into the soil like they're supposed to, say experts at the Michigan State University Extension.
  • Too much mulch directly over the root ball can keep water away from the tree's roots, causing them to dry up, stressing the newly planted tree, according to Edward F. Gilman, professor of Environmental Horticulture at the University of Florida.
  • Roots can also end up girdling the tree stem, which will kill it, Gilman says.
  • A mulch volcano invites "root rot and insect invasion," warns MSU.

The right way to mulch trees & shrubs—the doughnut

tree mulched the right way
Here’s a better way to mulch trees – a wide ring of mulch pulled away from the trunk's flare.

To help your new trees thrive, follow this mulching advice from university experts:

  • The best mulch for trees is wood chips, according to Dr. Linda Chalker-Scott, horticulturist and associate professor at Washington State University. But even raked leaves work well, says the Kansas State University Extension.
  • Don’t cover the flare at the trunk’s base. Keep mulch 6-12 inches from the trunk to prevent rot and let water reach the root ball easily (sources: MSU and the University of Florida).
  • Spread mulch in a 3- to 6-foot wide ring. Six feet is better for long-term growth, according to Kansas State.
  • Make the layer 2 to 4 inches deep and replenish yearly.

The trees you plant now can still be here in a hundred years—even longer—with good care. Just follow these tips and remember doughnuts, not volcanoes.