In nature, leaves and pine needles fall to the ground and create a thick layer of organic material that insulates the soil, conserving moisture and helping protect plant roots from changing temperatures. Mulch in the landscape and garden mimics this natural process, protecting plant roots from stress and thus improving plant health and growth. Mulches also provide an important aesthetic design accent to highlight your landscaping style.
Wood chips are a common organic landscape mulch. Organic mulches--those made of natural, previously living materials--slowly decompose. This adds organic matter and nutrients to the soil surface, which earthworms, insects and water deliver to the roots of your landscape plants. Properly aged wood chips are an excellent landscaping mulch, because they are commonly available free or inexpensively, stay in place without compacting or washing away and weather to a silver-gray that complements most landscaping schemes, according to the Virginia Cooperative Extension. Do not use wood chips that have not aged, however, as the decomposition process of green wood chips can damage nearby plants.
Pine needles, also called pine straw, are another attractive landscape mulch. They are often available free or can be purchased from garden centers. Pine needles can increase soil acidity, and the USDA Natural Resources Conservation Service recommends them for use around acid-loving plants like rhododendrons and blueberries. Pine needles are attractive and decompose slowly and, like wood chips, resist compaction, allowing water to continue to pass through into the soil, notes the Virginia Cooperative Extension. If enough pine needles are not available to bring the mulch to a sufficient depth, a 2- to 3-inch layer of shredded newspaper can be spread over the soil first, with a layer of pine needles added on top.
Pebbles are inorganic mulches that will not add to soil structure and nutrition, but they do serve to moderate soil temperature and moisture variations as well as add aesthetic interest to the landscape. The University of Rhode Island Landscape Horticulture Program recommends putting down landscape cloth or porous geotextiles first; these help warm the soil and block weed growth while still transmitting water and air to plant roots. An inorganic mulch like pebbles will hold the landscape cloth in place but will not encourage weed growth above the cloth. The cloth will help prevent the pebbles from migrating down into the soil as well. Pebbles or gravel do pose a risk of being thrown by lawnmowers. Avoid this with careful edging to keep the pebble mulch in place.