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Should I Be Using Mulch Around Trees?

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Question: Should I Be Using Mulch Around Trees?
Using mulch around trees -- particularly young trees -- can be beneficial. However, there are some DOs and DON'Ts to keep in mind when using garden mulch around trees....
Answer:

DON'Ts:

1. Don't fall into the trap of the dreaded "mulch volcano," especially with young trees.

You've probably seen mulch volcanoes on people's lawns. Folks build circular raised beds around their trees, then fill the raised beds with wood-chip mulch. The mulch gets steeper and steeper the closer it gets to the tree, which shoots out of the hole at the end like a lava eruption! In a typical mulch volcano, the mulch may be 2" high at the perimeter and 6" high up close to the trunk.

There are several problems with mulch volcanoes:

  1. Water runs off the sides of the mulch volcano and away from a young tree's base (which is where all its roots are, for now), thus depriving it of water.
  2. 6" of mulch is too deep. Much water that would otherwise reach the tree's roots gets trapped in the mulch.
  3. Excessive tree mulching invites rodent pests and diseases.
  4. Excessive tree mulching can even suffocate roots.

2. Don't mound up dirt or mulch around the trunks of trees.

Piling up mulch against tree trunks can cause harm to your trees: it invites diseases and rodent pests, such as voles. If you are mulching around a tree, start tapering the height of the mulch down when you get to within about 1' of the trunk, leaving the base of the tree free of mulch. It would even be better to have to weed this 1' than to risk damage to your tree, wouldn't it?

DOs:

1. Do apply about two inches of mulch around trees, especially young trees.

Mulching trees keeps down weeds, thus eliminating competition for water. In addition, much water that otherwise would be evaporated by the sun can soak down through a 2" layer of mulch to the soil around tree roots. Mulching trees also helps keep their roots cooler in hot weather.

2. Do use shredded leaves when possible in mulching trees, especially young trees.

There's nothing wrong with using wood-chip mulches. However, a shredded-leaf mulch has some advantages. First of all, it's free. When you rake up your leaves, put them through a leaf shredder or leaf vacuum if you already own one; otherwise, shred the leaves by running the lawn mower over them. Secondly, leaves break down faster than wood chips, thereby releasing nutrients faster. Young trees, especially, will appreciate those nutrients.

In the final FAQ of this series, we'll look into how to water trees -- an important step in winterizing them.

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