While I do have a compost pile, I wondered if it is OK to use grass clippings and leaves as a mulch. I have heard that they actually remove nutrients from the soil as they decompose and, therefore, shouldn’t be used as a mulch. It seems to me that they would be actually returning nutrients to the soil as they decompose. Please advise.
Organic mulches such as grass clippings do eventually return nitrogen and other nutrients to the soil. However, during the early stages of decomposition, the microorganisms responsible for the breakdown of the mulch require nitrogen and will steal it from the soil. This may cause a temporary nitrogen shortage to surrounding plants unless it has been supplied with nitrogen supplements such as cottonseed meal, bloodmeal, or urea.
If grass clippings are spread too thickly, they will heat up and make a hot, slimy mess. If they are too close to the stems of young, tender plants, this reaction can cause damage. Further, as the layer compresses, it can become tight and allow only anaerobic decomposition, often producing a bad odor in the process.
While some gardeners may disagree, grass clippings are not a preferred mulch. It’s best to compost them completely in a compost pile and use the resulting rich humus to enrich new or existing planting beds.