Mulching your trees

Ronald Dudley
Frederick County Master Gardener

When mulching your trees and shrubs think "Donut", not "Volcano".

You can maximize growth of new trees by having a mulched area under the trees rather than grass. Proper mulching of our trees is beneficial to the trees because the mulch reduces competition for nutrients and moisture and it adds protection from lawn maintenance equipment while creating an aesthetically pleasing landscape. However, excessive mulching of trees is detrimental to the health of the tree and is a waste of money and resources.

With mulch piled high against a trees trunk, creating a "Tree Volcano", the tree’s bark is compromised. To function properly, a tree’s bark needs to be exposed to the air. When mulch is piled directly against the trunk of the tree, the subsequent buildup and retention of moisture within the mulch pile softens the bark. This softening of the trees bark allows outside organisms like voles, insects, bacteria, virus and fungi to penetrate into the tree. The "Tree Volcano" method of mulching may also encourage some tree species to establish roots in the mulch pile rather than deep into the soil. This weakens the tree and makes it more susceptible to blowing down during a windstorm. Additionally, the "Tree Volcano" mulching method can lead to root death during dry weather, and delayed onset of dormancy in the fall and breaking of dormancy in the spring.

        Tree Volcano about 1 foot deep                         Inside a tree volcano


Correct Mulching of Trees.

Create a "Donut" of mulch with the trunk of the tree being in the center of the donut hole. It is best to place the mulch donut at the base of trees immediately after the tree is planted, but a mulch donut may be added at any time. If mulch is being placed around an established tree, care must be taken to not damage the tree’s root system.

How to apply mulch to the base of your trees:

1. Before you apply mulch, remove grass and weeds from around the tree.

2. The mulch donut is recommended to be as far out as the spread of the tree branches (the drip line), but at a minimum a 2-3 feet wide area around the tree trunk radius should be mulched.

3. Maximum depth of the mulch is 3 inches – the roots need to breathe. Taper the mulch layer to the grass at the edge of the ring.

4. Aged wood chips or shredded bark, are the best choices for mulch.

5. Mulch should never touch the bark of the tree!

6. As organic mulches decompose, replace the mulch as needed to maintain the mulches original depth.

7. When watering mulched trees you must be sure to water deeply to insure the water soaks not just the mulch, but flows through the mulch and percolates deep into the soil.

8. Larger trees, 10 inches in diameter and larger, do not need mulch, but if you do mulch them follow the same guidelines as outlined in steps 1 – 7.

           The tree donut (stones optional)                    The tree donut hole

Read other articles about tree care

Read other articles by Ronald Dudley