TOO MUCH MULCH CAN KILL TREES, by Larry Williams UF/IFAS Extension Agent

Mulch, when properly used, is a great thing for trees and shrubs. But too much mulch can be bad.

In today’s article, I’ll share with you information from Stan Rosenthal, UF/IFAS Extension Agent in Leon County. Rosenthal explains why overdoing it with mulch can result in tree decline/death.

Mulch has various benefits. It helps protect the soil from erosion as well as moderates soil temperatures. Mulch also protects against soil compaction. Believe it or not, when rain drops hit soil, they compact the soil. So mulch helps prevent this compaction. Mulching is also nature’s way of recycling tree leaves and converting them into nutrients and organic matter that helps improve soil structure that will facilitate better plant growth.

But over-mulching can have adverse effects. One common error is piling the mulch up deep against the tree trunk in what we often call “volcano mulching”.  With mature trees, volcano mulching can keep roots from getting enough oxygen, resulting in root death and decay. The mulch also traps moisture around the lower trunk, promoting rot. The excess mulch invites damage from rodents that chew the bark and can girdle the tree.  Too much mulch can also hide decay and dead spots on the lower trunk and major roots. Decay in this portion of the tree can cause the tree to become unstable.

On recently planted trees, it is especially important to avoid mulching right over the root ball, as this can interfere with water and oxygen reaching the roots. But mulch a little further out can help prevent lawn mower and weed whip injuries to the trunk of the tree and exposed roots. It also keeps competing sod away from the roots of trees. Another bonus of mulch is that well mulched areas catch and absorb more rainwater than bare soil. Try to tie mulched trees together in a bed for ease of maintenance and because trees grow best in groups.

On mature trees, keep all but a thin layer of mulch about twelve to eighteen inches from the trunk. From there outward, maintain mulch beds that are two to four inches deep out as far as you wish to maintain and find aesthetically attractive. Remember that roots can often grow two to three times as far outward as the branch spread of a plant. Any area of a tree’s spreading root zone that is covered by mulch is a good thing for the tree.

A natural forest has its own mulching process that recycles nutrients, absorbs rain water and maintains a cooler soil temperature on hot days. Mimic these areas by properly mulching. Just don’t over-mulch.

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