Rammed earth garden beds are made by compressing a damp mixture of approximately 70 percent sand, 30 percent clay, and a small amount of cement into an externally supported form or mold, creating a solid, earthen wall after the frames are removed. One of the benefits of rammed earth is that its high thermal mass absorbs heat during the day and releases it at night. My technique for building rammed earth garden beds makes use of local raw materials, is resistant to temperature changes and is remarkably cost-effective.
Construct rammed earth garden beds by using two frames — a box inside of a box with a 3 1/2-inch gap between the walls. Pack this gap with the earth mixture, then remove the frames, leaving earthen walls that are ready to hold your garden soil.
3 sheets of 4-by-8-foot plywood
4 pipe clamps, each 60 inches in length
1 bag of Portland cement
1 hand tamper (or optional power tamper)
Mix of local sand and clay
Start by constructing the framework. Cut all three of the 4-by-8-foot plywood sheets in half, resulting in six pieces of 2-by-8-foot plywood. Set two of the newly cut pieces aside. Cut the remaining plywood boards into the following sizes: two at 2-by-4 feet, two at 24-by-41 inches, and two at 24-by-89 inches. Save the leftover wood for a future project.
The external, larger box uses the two panels that are 2-by-8 feet and the two panels that are 2-by-4-feet, held together with the pipe clamps. The internal form uses the two 24-by-41-inch boards and the two 24-by-89-inch boards, braced with the twelve 2-by-4s. After the two frames are assembled, you will have two big boxes sitting on the ground, with a 3 1/2-inch gap between their walls.
Mix the sand and clay with 8 percent Portland cement and very little water. Layer the mixture between the framed walls, 8 inches deep at a time, and then tamp it down tightly. Repeat this process until the rammed earth is 3 inches from the top of the form. At this point, add a layer of concrete to the top to finish the process. The following day, strip away the wooden form and then fill the rammed earth garden bed with soil and top with mulch.
Penticton, British Columbia