Consider lava rock as a mulch in xeriscape gardens or around shrubs, succulents or other plantings that won’t change much over time. This type of rock is lightweight compared to traditional stone mulch, which makes it easier to haul and handle without professional help. Individual rock edges tend to be sharp. Stone mulch doesn’t ever break down or disappear—it’s a permanent addition to the landscape. Place it on a layer of landscape fabric to prevent rocks from sinking into soil.