Moss covered rocks are used as alternative ground covers, decorative features and are also found in rock gardens. The type of moss used to create these intriguing features is called rock moss, which is a common name for a number of Hypnum moss species. This type of moss often grows in thick sheets which can take up to ten years before reaching its maximum potential. Though thickness is suitable for lawns, gardeners interested in rock moss don't strive for a thick moss covering. Most gardeners aim to see a balance of rock and moss. Achieving the desired appearance can take a few weeks, when provided with proper growing conditions. Moss tolerates a swath of temperatures and grows in USDA hardiness zones 4 through 10. More than temperature, moss requires high humidity and minimal competition. This is why moss grows well on rocks, no other plants will compete with it on that barren surface. Moss is low maintenance and will thrive with minimal care. Rock moss is green, with tiny leaves and a sponge-like texture. It can withstand light foot traffic and is suited for growth on and between stepping stones, stairs and other rock or stone pathways and surfaces. When cultivated in rock gardens, rock moss adds depth to the landscape and provides color when annuals or other flowers are dying back. The key to establishing moss on stone is to keep the growing medium and the moss itself moist. To grow the moss on a rock surface, gardeners create a slurry. There are a number of recipes for moss slurry but each involve taking a certain ratio of moss and water, fragmenting the moss and then spreading the slurry on the rock surface. The slurry should be kept moist until the moss begins to take hold, which can take up to a month.