Mulch helps preserve water and regulate the temperature in your soil but it also prevents the growth of weeds, protects soil from compaction, cuts down on erosion and, if organic, feeds your soil. As the mulch decomposes, it provides that vital organic matter to your soil, encourage microbe growth and shelter earthworms. All that organic matter keeps your soil loose so that it can retain moisture and promote root growth.
Mulch is a protective layer of material that is spread 3-6 inches deep on top of exposed soil between plants. Mulch is by far the best way to preserve the water in your soil and can be a very effective way of feeding your soil and regulating growing temperatures. Mulch can be almost anything: straw, grass clippings, corn cobs, river stones, pea gravel, chipped bricks, bark chips, leaves, peat moss, seaweed, wood ashes, sawdust and so on.
Nature abhors uncovered and exposed ground. Walk out into nature and look down. In a healthy ecosystem you will find very little, if any, bare ground. Nature will always try to cover soil with either plant growth, decaying matter or even inorganic matter. Trees drop their leaves and cover the floor of a forest for example. You’ll want to imitate the same process in your garden.