How to Mulch around Trees – and Why

Why you might mulch around trees

Existing trees don’t really need mulch, but there are three good reasons to mulch one anyway:

1. Aesthetics – it serves as sort of a frame around the base of the tree.  It’s tidy.
2. Weed control – weeds are difficult to remove around the base of a tree unless you hand weed; this is impractical in a large landscape
3. Protection – if there aren’t any weeds or grass near the trunk, you won’t whack it with the lawnmower, string weeder, and so on.  This was, I believe, the original reason that commercial landscapers began mulching around trees. Especially on trees with thin bark (e.g., Japanese maples and beech) you can cause a lot of damage just by banging into it.  This is sometimes called “lawnmower blight” in a rare flash of humor from plant pathologists.

How NOT to mulch – like this photo!

If you do want to mulch established trees, this is how should it be done:

1. Keep the mulch away from touching the trunk by 4 to 6 inches. Mulch that actually touches the trunk encourages damage by voles (mouse-like rodents) that may chew on the bark under cover of the mulch. It may encourage fungal diseases because the bark of the tree is periodically wet from the mulch. It encourages roots to grow above the soil into the mulch, which over time results in roots that may cross sections of the base of the tree, slowly reducing water uptake and eventually girdling and killing the tree.  Literally killing the tree with the “kindness” of mulching. Planting too deeply in the first place, and girdling roots are major causes of premature death of trees. In other words, don’t copy the “mulch volcanoes” you see sometimes done by landscape crews, where they pile it up against the trunk of the tree. Pictured here is an example of the infamous “mulch volcanoes” – don’t mulch like this!
   
        
2. Apply the mulch so it’s level, and no deeper than three inches.

This will protect your trees from the lawn mower and help prevent weeds, while creating an attractive accent at the base each tree.

by Larry Hurley

Photo credit: Extension Horticulture.