Mulch is any material applied to the soil as a protective covering. Its job is to keep down weeds, protect roots from temperature extremes, and retain moisture. Mulching not only benefits the soil and the roots, but saves you time and water. Apply mulch right after you plant the garden. Spread it between planted rows and pull it up to the plants as they grow.
In areas that get only light frost in the winter, apply mulch before frost is expected, to protect crops left to overwinter in the ground.
Where soil freezes hard, place a winter mulch on perennial vegetables after the ground has frozen. This usually occurs after the second hard frost. By insulating the ground, the mulch keeps it frozen through cycles of warmth and freezing cold that damage plants later in the season. Materials suitable for winter mulching are pine boughs, marsh and salt hay, and straw. Apply the winter mulch in a layer thin enough so you can see through to the plant and soil. Remove the mulch when the first signs of new growth appear.
Mulches composed of materials that once were living are organic mulches. Over the course of the growing season, an organic mulch decomposes and adds humus to the soil. Tilled back into the soil at the end of the season, or before planting the following season, an organic mulch conditions and restores the nutrient content of the soil.
Probably the most valuable mulches for vegetable gardens are compost and composted manure. Both add nutrients as well as humus to the soil.
Most environments offer “found” materials that make fine mulch once they are composted—ground leaves, weeds that have not gone to seed, rotted sawdust, or grassy seaweed. Grass clippings, shredded newspaper, decaying straw, rotted hay, and pine needles may be applied as mulch without composing. Vary the type of organic material you use for mulching to vary the nutrients added, and check the soil pH annually.
Garden centers sell organic mulches by the bag, the bale, and the truckload. Peat moss is sometimes used as a mulch, but it dries out, cakes, and resists the penetration of rain; rewetting it is tedious. Better and more attractive choices are cocoa hulls, pine needles, composted sawdust, and finely shredded bark. Avoid the coarser mulches used on beds of ornamental plants, such as large wood chips. They look good but they do not decompose by the end of the season, and that makes it difficult to till the soil.
Do not overdo organic mulches. Applied more than 4 inches deep, many mulches cause root rot, stem rot, and suffocation. As the season advances, replenish the mulch to maintain the original depth. Apply straw and other loose mulches 6 to 12 inches deep; they will settle quickly.
Plants set very close together grow into a living mulch. This is a good way to mulch closely spaced wide-row gardens. The leaves form an overhead canopy thick enough to shade the soil and reduce weed growth.
Black plastic film is a popular synthetic mulch, but it is being challenged by thin, loosely woven fabrics called geotextiles, which keep down weeds but let air and water pass through to the soil.
Installation is the same whether you use plastic or geotextiles. Before seeding or planting, lay the material over the ground and weight the edges. Cut slits or X’s in the material where you want to place plants or seeds.