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Mulching for Tree Health

Adding mulch around trees can provide a wealth of benefits. Not only does mulch prevent excessive water loss and provide weed control, it also protects trees from lawn mower damage and soil compaction. In addition, many homeowners who have a difficult time growing grass have found that creative mulch beds can greatly enhance the aesthetics of their property.

While the benefits of mulch are numerous, it is very important to remember that poor mulching practices can also cause significant tree damage. Mulch can hold between 5 and 10 times its weight in water, so too much mulch around a tree may actually inhibit oxygen adsorption by the tree’s roots. It is also very important to avoid piling mulch directly on and around the base of a tree's trunk or root flare. This troublesome practice, known as "volcano mulching," provides an ideal habitat for small mammals, insects, and pathogens which can damage a tree. Volcano mulching also traps moisture around the tree trunk and root flare, leading to decay and, eventually, structural failure.

To ensure that your mulching practices provide tree benefits and not drawbacks, please consider the following three recommendations:

1. Avoid using artificially colored or exotic wood mulches. Chemicals in colored or treated mulch may have a non-desirable affect on soil chemistry. Mulch made from Redwood or Cedar trees can significantly change soil pH. It's best to use a hardwood mulch.

2. Never pile mulch around the base of a tree. As stated above "volcano mulching" can cause serious problems for your trees. Fortunately, it is entirely avoidable. Simply do not mound mulch at the point where a tree's trunk meets the roots. Mulch should be spread a consistent depth over as much of the tree's root system as possible, but it should not touch the tree's trunk.

3. Be very careful not to add too much mulch. For trees in dry, upland locations, 3 to 4 inches of loose mulch is ideal. In locations that tend to be wet, maintain a mulch depth of no more than two (2) inches. Before replenishing a mulch bed, be sure to rake the bed and determine the depth of the existing mulch. While mulch does decompose, it is a common mistake to accumulate excessive mulch by periodically adding fresh mulch. If you like the look of fresh mulch, simply remove the old mulch before adding the new.

If you have any questions about mulching or any other forestry-related issues, please contact Tony Gliot, the Village Forester, at (847) 883-8600.