If you have ground that is not workable for a flower or garden bed, such as clay, rock, or is a very thin layer of soil, you have two choices. You can dig down and remove the area, or you can build plant beds above the ground. The cheaper method is to build plant beds. You can also install a plant bed in any location on your property. You can also build plant beds as deep as you need. The example here is for a 1-foot deep bed.
Prepare the ground. Clear out any debris, such as rocks or branches. Place your first stake in a corner of where you what the bed. Set the end of the measuring tape at this stake and extend it 3 feet in one direction. Place your second stake at this point. Move the end of the tape measure to the second stake. Extending the tape measure at a right angle, move 12 feet from the second stake. Place the third stake at that point. Extend the tape measure again at a right angle to that stake 3 feet so that you are standing across from the original stake. Place the fourth stake here. This is your boundary.
Lay out a 3-inch layer of gravel inside the boundaries of the stakes. Use a claw rake in a back and forth motion to spread the gravel into place. This will become your drainage system. Keep the gravel loose so water can flow through to the ground below. Cover the entire surface so that moles and other animals cannot reach the roots from underground.
Place the beams. Place the first 3-foot beam so that the stake is at the inside of one end. Place the first 12-foot beam against the edge of the 3-foot beam so that the end of the short beam butts against the inside edge of the longer beam. Place the next 3-foot section at the opposite end of the 12-foot piece. The end of the long piece should butt the inside edge of the second 3-foot section. Place the next long beam at the end of the short piece so that the end of the short beam meets the inside edge of the second long beam. This will give you four sides with the ends of each piece butting against the inner edge of the beam before it.
Standing outside of the box, place the first short beam of the second row so that the left end overlaps the 12-foot beam below it. Match up the edges. Place the other three beams in succession as you did in the previous step with the end of the beam meeting the inner edge of the next beam. Place the first short beam of the third row as you did for the first row. Match up the ends for this row as you did for the other two. You will notice that the wall is now interlocking and is not prone to falling over.
Fill in the area with soil. Use clean fill or as close to clean fill as possible. This will have very little or no rock in it. This will help allow the roots to grow. Fill the plant bed up to the first row of beams and disperse with the claw rake. Tamp down the soil with the back of the shovel. Repeat the filling process with each layer until you reach the top; do not tamp down the final layer. This will allow you to fill in as much soil as the plant bed can handle and eliminate most of the settling that occurs with loose soil.
Level off the surface. Use the claw rake to even out the top layer of soil. Keep this layer loose so you can plant seeds and seedlings.