Many practitioners have found that including a mulch layer (often of native hay or mesquite chips) over seeded areas can facilitate establishment of desired species and reduce weed encroachment. When acquiring mulch, ensure that it is weed free by purchasing it from a certified producer. Most organic mulch types enhance soil nitrogen which disproportionately benefits invasives and should be avoided in arid systems. Gravel or rock mulch, thinly applied with visible soil in between the piece of aggregate can provide benefits expected from organic mulches, such as moisture retainment  without nitrogen addition into the system . Woodchips have been found to limit the growth of native species.