University of Maryland Extension

Excessive Mulch

Mulches in general, are beneficial to plant growth, however, if the wrong kind or too much is used they may be detrimental to plants. Keep organic and synthetic mulches several inches away from the trunk to prevent excessive moisture and the possibility of crown rot diseases. Organic mulches should not exceed three inches in depth. Although organic mulches break down over time they should only be replaced as needed to maintain their original depth.

Excessive mulching may encourage certain plant species to establish roots in the mulch layer rather than the soil underneath. Over time this can lead to root death due to desiccation during dry weather as the mulch dries out more quickly than the soil. Irrigation of mulched plants should be carefully monitored for water percolation through the mulch layer into the soil. Insufficient watering may only wet the mulch layer while the soil remains dry. Excessive mulch may delay the onset of dormancy in the fall by keeping root zone temperatures warm. In contrast, excessive mulch may prevent the breaking of dormancy in the spring due to cooler root zone temperatures.

Resource: Mulch


(PDF) 426-724 - Mulching for a Healthy Landscape (from VA Cooperative Extension)
(PDF) HG 803 Mulch Problems: Commercial Landscape Series
(PDF) ARG97-27 - Mulch - What's Growing in My Landscape Mulch?

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