Use the largest, flattest rocks to form the wall's base. Lay this base rock at least to the depth of one rock below the soil surface. In some cases, it is desirable to begin the rock wall well below the soil surface. Use the widest stones on the lower portion of the wall with smaller rocks for the top. Rocks 2 to 4 inches thick and 8 to 12 inches long will provide a good wall if properly placed.
Larger rocks are more difficult to hold in place.
Adding large amounts of soil between layers of rock will weaken the wall. When plant materials are to be used in the wall, place clean topsoil between the stones. If desired, small pockets in the wall will permit vegetation to establish a firm root system throughout the wall and provide added erosion control. However, large woody plants are not desirable. Properly constructed rock wall.