They prevent loss of water from the soil by evaporation. Moisture moves by capillary action to the surface and evaporates if not covered by a mulch. Mulching will prevent crusting of the soil surface, thus improving absorption and percolation of water into the soil and at the same time, eliminating erosion. Maintenance of a more uniform soil temperature can be obtained by mulching. The mulch acts as an insulator that keeps the soil cool under intense sunlight and warm during cold spells.
Organic materials used as a mulch can improve soil structure and tilth.
As it decays the material works down into the topsoil. Decaying mulch also adds nutrients to the soil. Mulches also add to the beauty of the landscape by providing a cover of uniform color and interesting texture to an otherwise drab surface. Dark colored mulches widen the pupil of the eye, allowing more of the sensible light from flowers to enter the eye. Consequently, those dark mulches give plantings a more attractive appearance.