Mulch helps minimize weeds, conserve moisture, moderate soil temperature, and make your yard look good. Mulched plants generally grow much better than similar, unmulched plants in the same garden. The two basic kinds of mulch are organic, such as shredded leaves and bark, and inorganic, such as gravel.
Choose appropriate mulch. Organic mulch adds to the health of your soil, but attracts insects and may be flammable. These mulches decay at different rates, depending on the size and composition of the pieces and the climate. Large chunks of bark last the longest, while grass clippings and shredded leaves need frequent replacement. Inorganic stone or sand mulch is fireproof and suitable for arid and coastal landscapes, but may attract cats and ants.
Determine mulch area. The sizes of the plants and turning radius of your mower determine the size and shape of the mulch area. Calculate the area you need to cover in square feet, then use the mulch calculator to determine how much mulch you need. Mulch out to the drip line or edge of the widest branches, if possible. Group shrubs and trees into beds, instead of mulching around individual plants, to save mowing time and unify your landscape plantings.
Eliminate weeds and turf. Clear all the weeds and grass from the area you intend to cover to prevent them from growing up through the mulch. Pull weeds by hand or hoe them out. Remove lawn grass by slicing under it with a spade, being careful to dig only into the top 2 to 3 inches of soil. Shake the soil out of the turf before discarding it to maintain the soil depth around your trees and shrubs.
Spread mulch. Cover the cleared area with 2 to 4 inches of mulch. Rake the mulch into a flattened doughnut shape, keeping it at least 6 inches away from the trunk or stems of the plant. Make a neat outer edge by leaving a small gap between the mulch and the edge of the surrounding lawn.
Maintain mulch. Replace mulch as needed during the growing season to maintain the 2- to 4-inch depth. Rake up and replace organic mulch in the spring, especially around roses and fruit trees.
Lay landscape fabric under gravel mulch to help prevent weeds. Never use plastic mulch for trees or shrubs because it prevents water and air from reaching roots.
Preferred mulches include bark chunks, shredded and composted fir bark, and weed-free straw. Avoid weedy hay and water-repellant peat moss as well as toxic mulches made from pressure-treated lumber, eucalyptus, walnut, redwood, or cedar sawdust. Do not use mulch that smells like vinegar, ammonia, or sulfur.
Photography by Suzanne DeJohn/National Gardening Association