Q. Can I use grass clippings as mulch?
A. Yes and no. Like other organic mulches, grass clippings will conserve moisture, suppress weeds and feed the soil, but you'll want to heed the cautionary notes first before you think about applying them. Here's why you may not want to use them as mulch:
If you've recently applied herbicides to the grass, you could be introducing contaminants into the garden bed that would harm your plants. Some herbicides are exceptionally long-lasting. And if you want to use grass in a vegetable garden, you want it to be free of both herbicides and insecticides, especially those that are not labeled for vegetable gardens.
As grass clippings decompose, they produce a lot of heat, which could affect plant growth and lead to disease problems.
Grass clippings tend to compact a great deal, so you'd need to apply many inches in order to achieve an effective layer of mulch. Creating a deep bed of grass mulch, however, would exacerbate the heat and decomposition issues.
If your grass clippings contain aggressive grasses like Bermuda, you could be introducing a weedy grass just where you don't want it.
Grass clippings can become very smelly as they decompose.If you feel you must remove the clippings from your lawn, the better place for them is in the compost pile, where they can raise the heat — and accelerate the decomposition — of the pile. If you want to experiment with using some grass clippings in your garden beds — and they're free of herbicides, insecticides and noxious weeds — spread a couple of inches out over the bed, let them dry for a day or two, then cover with a traditional organic mulch like shredded bark.
Ideally, though, the best place for your clippings is right in your lawn, where they return nutrition to the soil. Grass clippings contain 4 percent nitrogen, and smaller amounts of phosphorus, potassium and other nutrients. Studies have shown that up to one half the nitrogen applied to the lawn as fertilizer is removed when grass clippings are removed.
Clippings break down quickly in the lawn, provided not more than a third of the grass blade is removed with each cutting, and you haven't mowed when the grass is wet. If you have mowed when the grass is high or wet, just re-mow over the grass clippings that have clumped or matted.
