Manure vs. Mulch

The Role of Organic Matter

• Organic matter is the remains of once-living organisms that are in the process of decomposition. Mulches and manures are two forms of organic matter with very different characteristics. Manure is the waste of domestic animals, and has a high nutrient content compared to mulch, especially nitrogen. Mulch is the shredded remains of plant material and is composed almost entirely of carbon-based compounds, along with tiny quantities of other nutrients. The rate at which organic matter decomposes is largely dictated by nitrogen content -- woody mulches can take years to break down, while rich manures can decompose in a few months. Both, however, eventually decompose completely to form humus, a highly stable substance that is the physical basis for soil fertility.

Applications

• Manure is usually composted before it is applied to the soil. Composted manure works best when it is mixed into the soil before planting, though it can be applied on the surface, as well. Mulch should only be applied to the surface and is used to slow the loss of soil moisture and suppress weed growth. Most gardeners prefer the appearance of mulch over bare earth, and it is available in many colors and textures with different aesthetic qualities. Composted manure is an instant source of nitrogen and other nutrients for plants, while mulch nourishes the soil very slowly as it breaks down.

Sources

• The source of mulches and manures determines their physical characteristics and, in the case of mulch, also determines its aesthetic qualities. Manure from large herbivores like cows and horses has a moderate amount of nitrogen, while poultry manure is extremely rich in nitrogen and other plant nutrients. Leaves and grass clippings are two forms of mulch that are relatively high in nutrients and decompose very quickly, compared to woody mulches made from bark or ground up wood waste. The color of woody mulch depends on the source material, though it is often died to have a uniform color. Pine straw, another source of mulch, has a uniform and attractive appearance but increases the acidity of the soil as it decomposes.

Cautions

• Fresh manure generally has too much nitrogen for plants and "burns" the roots if applied directly, especially chicken and pig manure. Caution is needed when working with raw manure because of the potential for pathogens. Plus, the odor can be very offensive -- a major consideration when using manure in the home landscape. In comparison, mulch is a relatively benign, stable substance that is safe to handle. But mulches such as wood chips can temporarily reduce the availability of nitrogen in the soil and should be used sparingly around vegetables and other tender annuals unless used in conjunction with nitrogen fertilizer. One final caution is to avoid piling mulch directly against the base of trees, shrubs and woody vines because it often leads to fungal diseases in the root crown.