The benefits of an organic mulch are many, but the most important is the reduction of water loss by reducing surface evaporation. Organic mulches will also prevent annual weed growth by establishing a physical barrier so that weed seeds blown in will have difficulty establishing themselves. Likewise, seeds already within the soil will have difficulty penetrating upwards through the mulch. An organic mulch will also insulate the soil surface against temperature fluctuations. In summer, a layer of mulch will cool the soil making it a more hospitable environment for root growth and beneficial micro-organisms.
Mulches can also prevent wind and water erosion of soil.
As they break down and decay, organic mulches add to the soil fertility and improve its structure. Mulches have design benefits as well. Many as aesthetically pleasing and provide visual interest through texture and color. At the same time they function to unify a planting or bed. This is especially true when the bed if first planted and the plant material is small and occupies only a small proportion of the space it will eventually use when mature.