Purpose, availability, cost, and final appearance of a mulch are the determining factors in choosing the type to use. The more commonly used mulches are evaluated below.
Commonly Used Mulches
A 2-inch layer of sawdust provides good weed control. If applied around growing plants, add 1/2 pound of actual nitrogen per 10 cubic feet of sawdust to prevent nutrient deficiencies. Fresh sawdust contains a great deal of carbon and very little nitrogen, and its breakdown requires that microorganisms take nitrogen from the soil. There is a problem with crusting of fresh sawdust, with resulting impermeability of rainfall. Sawdust is best used for garden paths and around permanent plantings. Readily available from sawmills, it tends to be inexpensive.
A 2- to 3-inch layer of bark provides good weed control, is slow to decompose, and will stay in place. Shredded bark decomposes more quickly than chips. Wood chips may be available free or for a small fee from professional tree pruning services, but many people find them less attractive than bark chips. Bark chips can be purchased in large bags at retail stores. These make a very attractive mulch and are especially recommended for mulching around trees and shrubs.
A 6- to 8-inch layer of hay or straw provides good annual weed control. These materials decompose quickly and must be replenished to keep down weeds. They stay in place and improve the soil as they decay. Avoid hay that is full of weed seed and brambles. Fresh legume hay, such as alfalfa, supplies nitrogen as it breaks down. Hay and straw are readily available in rural areas, but city dwellers may not be able to obtain hay. Straw can be purchased at most garden centers, often commanding a high price. Both are recommended for vegetable and fruit plantings.
Baled pine needles also are found in garden centers. They make an excellent mulch around shrubs, trees, and in other areas when a long-lasting mulch is desired. Readily available.
A 2-inch layer of grass clippings provides good weed control. Build up the layer gradually, using dry grass. A thick layer of green grass gives off excessive heat and foul odors rather than decomposing. However, in limited quantity, clippings decompose rapidly and provide an extra dose of nitrogen to growing plants, as well as making fine humus. Avoid crabgrass and grass full of seed heads. Also, do not use clippings from lawns that have been treated that season with herbicides or a fertilizer/herbicide combination. Grass clippings can be used directly as mulch around vegetables and fruit plants or can be composted. They are an excellent source of nitrogen to heat up a compost pile, especially for those gardeners without access to manures.
A layer of leaves, 2 to 3 inches thick after compaction, provides good annual weed control. Leaves decompose fairly quickly, are easy to obtain, attractive, and improve the soil once decomposed. To reduce blowing of dry leaves, allow them to decompose partially. Highly recommended as a mulch.
A 2- to 3-inch layer of peat moss gives fair to good weed control. However, peat tends to form a crust if used in layers thick enough to hold down weeds. It is very difficult to wet and tends to blow away if applied dry. Peat also is a relatively expensive mulching material.
A 2- to 3-inch layer of compost is a fair weed control. Most compost, however, provides a good site for weed seeds to grow. It is probably better used by incorporating into the soil. A layer of compost can be used on overwintering beds of perennials, such as asparagus or berries, to provide nutrients and help protect plant crowns.
A 2- to 3-inch layer of these materials provides fair weed control, but both have a tendency to be easily blown by the wind. Peanut hulls stay in place somewhat better than corn cobs. A heavier mulch, such as partially rotted hay or straw, can be used on top to hold down the lighter materials. Recommended if readily available in your area.