Properly constructed raised beds provide many benefits, including better drainage, fewer weed problems and control over the quality of the soil. A bed raised by as little as 3 or 4 inches aids in drainage, particularly if you have heavy clay or other types of soil unsuitable for gardening. The beds do dry out more quickly than traditional beds, but they also warm up faster in spring and allow you to plant some warm-weather plants and vegetables sooner.
Drive a 3-foot stake into each corner of the raised bed site. Place a concrete cinder block over each stake, so the stake passes through the hole in the cinder block, to form each corner stone.
Place a row of cinder blocks between each corner stone to form the four walls of the raised bed. Stack a second row of cinder blocks on top the first if you want a deeper bed.
Dig out the topsoil inside the bed to the depth of one shovel blade. Place the soil into a wheelbarrow. Dig down to a second shovel blade depth, loosening the soil but not removing it.
Combine the soil in the wheelbarrow with an equal amount of compost. Place the compost and soil mix back into the bed.
Add additional compost or topsoil to the bed as necessary to finish filling it. Mix the additional compost in with the existing soil. Fill the bed to within 3 inches of the top of the cinder block walls.