They may reduce erosion but are themselves sometimes subject to erosion by wind because they are light or by water because they float. They can reduce water loss from the soil but, because they are porous and absorb water themselves, are not as effective in this as the inorganic mulches. They can help maintain stable soil temperatures, but in the case of finer particle and decomposed organic mulch, plant roots may grow in the mulch material where they are again exposed to drying and temperature changes. This does not make them inferior to inorganic mulches but does reveal the differences. Organic mulches do not usually become as hot as the inorganic mulches and are not as likely to cause heat injury to plants and may not hold heat as long into the night.
Organic mulches decompose releasing nutrients into the soil.
This enriches the soil but requires that the organic mulch be replaced periodically. Organic mulches create a good environment for earthworms and, because of the action of the earthworms, soil permeability is enhanced. As organic mulches decompose, they release carbon dioxide into the soil. This can injure some of our arid lands plants which are adapted to well-aerified soils containing high levels of oxygen in the spaces between soil particles. Such plants do poorly when mulched with organic mulches.