Retaining Walls Made of Big Rocks

Dig a trench with a shovel for the boulder retaining wall that allows 8 inches for a base plus half the height of the boulders you plan to use. Line the bottom and backside of the trench with landscape fabric. Use enough fabric to line the entire backside of the rock retaining wall. This prevents weeds from growing and it also prevents soil from working in between the stones.

Pour sharp gravel into the trench and compact it well with a hand tamper. Set the first row of boulders in place inside the trench. Put the large stones as close together as possible. Wedge smaller stones in openings to stabilize this row. The boulders are set when you can stand on them and they don’t wobble.

Mix mortar mix according to package directions. Place mortar 1/2- to 1-inch thick across the top back portion of the boulders in the base row with a trowel. Set boulders on top of the base row, working smaller stones in between the larger ones, as necessary, and staggering the larger boulders. Keep the mortar on the back portion of the stones to create the appearance of a dry stack stone wall. When this row is complete, none of the stones should move.

Continue building the wall until it is the desired height. Continue to check that none of the stones move when you stand on them. Finish the wall with a row of flatter stones to give the appearance of a row of capstones.

Fill in the soil behind the wall, pulling the landscape fabric up behind the wall as you place the dirt. Tamp the soil well every 6 inches or so. If you prefer, fill behind the wall with small stones and compact them. Add soil only in the last 6 to 8 inches behind the wall.