Dig a 12-inch-deep trench that is 10 inches wider than the landscape timbers with a flat shovel. Move along the trench with a level to even out the soil on the bottom of the trench.
Add 6 inches of gravel to the trench. Move along the trench with a level to even out the gravel on the bottom of the trench. Use a hand tamper or plate compacter to compress the gravel and soil at the bottom of the trench.
Drill a ¼-inch hole 6 inches from each end of the landscape timbers for the bottom layer. Drill additional holes every 4 feet.
Drill weep holes in the bottom course of the landscape timbers with a ½-inch drill bit at 4-foot intervals from the front to the back of each timber.
Place landscape timber on top of the gravel, 2 inches from the front edge of the trench. Place a level on the landscape timber to position it evenly.
Secure with 4-foot sections of rebar driven into the pilot holes with a sledgehammer.
Place a second course of landscape timbers on top of the first course, so the join below is at least 4 feet from the end of the timber on the second course. Align the front of the second course of timbers ½-inch behind the front of the previous row of landscape timbers. Attach the second course to the first course with landscape spikes driven in 6 inches from each end and at 4-foot intervals along the timbers.
Lay landscaping fabric behind the wall. Pour 2 inches of gravel on top of the fabric.
Add another course of timbers following the instructions in Step 7.
Place a perforated pipe in the trench behind the wall on top of the gavel. Cover with 4 inches of gravel. Wrap the landscaping fabric around the gravel so the gravel is completely covered with landscaping fabric.
Create a "dead man" by making a T shape with two 4- to 5-foot sections of landscape timbers. Secure with landscaping screws. Place the lower end of the dead man ½-inch from the front of the wall with the rest of the dead man horizontal and behind the retaining wall.
Dig out the area where the cross for the T will be behind the wall. Place a level on the dead man and level it into position by adding or removing soil. If soil is added, tamp to compact. Insert two landscaping screws through the end of the dead man into the landscape timbers on the course below.
Add a dead man every 6 to 8 feet along the wall and for each subsequent course of landscape timbers.
Backfill with soil behind the wall after each course of landscape timbers. Tamp each layer with a hand tamper or plate compacter.