Landscape mulch materials vary in their suitability for various uses. Impermeable plastic mulch has a function in the landscape, but is very often misused. It may be used in areas where the soil must be kept dry, for example, next to a foundation where termiticides have been applied and where you are channeling harvested water from one area to another. Otherwise, permeable weed barriers, bark, gravel, and other porous mulches are better because they allow water and oxygen to pass to plant roots. Dust will eventually collect over the weed barrier fabrics and allow growth of some weeds, so it is not a perfect solution, but these porous fabrics are useful for weed control when the bark or gravel covering it is less than 3 to 4 inches thick, or annual weed potential is great.
Organic mulches keep the soil moist and reflect less heat.
They work well with plants adapted to cooler microclimates. Bark mulch should not be used on steep slopes or in drainage ways because it washes away in heavy rains. Some plants native to very well drained soils grow better in gravel mulches. Remember, rock mulch becomes very hot in our climate and can injure or limit growth of some plants. Ultimately, the mulch should be shaded by landscape plants that will provide environmental cooling.