Think of it as insulation. Covering the bare soil around your plants minimizes evaporation and lowers soil temperature-major water savers. But mulching also smothers weeds, improves soil, and gives landscaping a neat, finished look. Overall, it’s one of the best things you can do for your garden.

Mulches can be organic or inorganic. Organic materials-leaves, straw, bark, sawdust, peat moss, grass clippings, pine needles, even layered newspapers-keep working as they decompose, aerating and enriching the soil. But because organic matter consumes nitrogen as it breaks down, you’ll need to add fertilizer to replace this essential nutrient.

A good layer of organic mulch must be thick enough to insulate the soil and keep weeds from rooting, but not deep enough to harbor pests or suffocate your plants. (Roots need air, too.) Generally speaking, the chunkier the mulch, the deeper it should be, anywhere from 1 to 6 inches. In most cases, 3 to 4inches is plenty. Always keep stems and trunks clear of mulch and soil.

Inorganic materials, such as rocks or plastic, eliminate weeds and last longer than organic mulches, but of course they don’t add anything to the soil. If you decide on black plastic, either old-fashioned polyethylene or gas-permeable polypropylene, you’ll want to add a decorative layer of bark or neutral-colored rocks on top. And be sure to puncture the plastic a few times to let water in. In San Diego, mulch in the early spring to retain the moisture from winter rains-or anytime you’d like to control weeds or freshen your gardens appearance.