A layer of organic material several inches thick buffers the soil against compaction from the harsh effects of heavy rain and baking sun, and helps the soil retain oxygen so it can support vigorous plant roots. It improves any soil by blending valuable organic material, or humus, into its top layer as the mulch gradually decomposes.
In nature, soil is always protected by a covering of organic material. Layers of leaf litter in the woods, and blankets of waving grasses on the plains, prevent erosion and absorb rainfall, just as your lawn and groundcover beds do. A layer of organic mulch provides similar protection to soil that isn't covered by plants. In your landscape, it forms an attractive cover that discourages weeds and masks imperfections.
More importantly, it helps conserve water by absorbing rainfall and preventing runoff. Soil covered by a layer of organic mulch stays damp much longer between rains or waterings because the mulch blocks evaporation.
Mulch protects nearby plants, too. A good layer of organic mulch between newly planted groundcover plants discourages weeds during the time the plants need to grow larger, knit together, and cover the soil on their own.
Trees and shrubs thrive on mulch, too. Circles of organic material under them not only condition the soil and improve its fertility, but they also create a barrier to prevent injury to their trunks and stems from lawn mowers and string trimmers.
A layer of organic mulch on the bare soil in your yard also contributes to the general health and vigor of the entire landscape because it shelters many kinds of beneficial organisms. For example, ground spiders and ants nest in rich organic material along the edges of lawns. From there, they prey on pest insect larvae and eggs in the soil under the lawn and garden beds.
Avoid spreading mulch too thickly. Anything over 2 or 3 inches threatens to become a suffocating blanket that blocks air and moisture from the soil. This causes plant roots to gravitate toward the soil surface in search of these essentials. In cases where surface tree roots are a problem, mulch lightly to improve the appearance of the yard, but don't try to bury the roots.
Organic mulch inevitably breaks down over time, and the mulch layer becomes thinner. Expect to add to it periodically, usually in the fall, to restore it to a 2- to 3-inch depth.
Shredded paper also makes a suitable mulch for protecting soil and discouraging weeds. If it becomes unsightly when rains wet it down, cover it with a thin layer of leaves or bark nuggets.
During the winter, fluctuating temperatures alternately freeze and thaw the soil. This often disturbs plant roots and may heave bulbs or plants out of the soil. A winter mulch does not prevent soil from freezing, but it provides insulation to maintain more even low temperatures.
Continued on page 2: Types of Mulch