How to Build Basalt Retaining Walls for Landscaping

Dig a trench along the base of the hill that measures 12 inches wide and 6 inches deep, using the shovel or spade. Smooth the soil at the bottom of the trench.

Dig into the hill behind the trench to remove the grass and expose the soil.

Pour 2 inches of gravel into the bottom of the trench to improve drainage. Smooth the surface of the gravel and tamp it down.

Lay the first course of basalt stones into the trench on top of the gravel. Use the largest stones you have to provide a more stable base.

Set the second course of stones on top of the base course. Stagger the stones in the second course so the joints between them don't line up with the joints in the base course. Set the stones in the second course slightly back from the stones in the first course. You want the top of the wall to lean away from the base at a rate of 2 inches for every foot of height to improve the stability.

Lay a third course of basalt stones onto the wall. Install deadman stones every 6 feet into this layer. Deadman stones are large, flat stones installed perpendicular to the wall, with the back edges extending away from the wall. The deadmen help stabilize the walls by acting as anchors.

Fill the space behind the wall with soil and compact it.

Continue to build the wall until you reach the desired height, using the same process. Install deadmen every four to five rows. If necessary, shape the stones by chipping away at them with a rock hammer.

Fill the last 3 inches of space behind the wall with an equal mix of topsoil and compost, if you're planting flowers or other plants behind it. Otherwise, install sod on top of the soil.