Raised beds give you control. You decide the soil, drainage is better, the soil warms earlier in spring, and there is less bending. They are the easiest way to get a productive garden going on poor ground or a small lot.
Sizing a bed
Keep beds no wider than four feet so you can reach the middle from either side without stepping on the soil. Length is up to your space. For depth, aim for at least ten to twelve inches, which suits most vegetables, and go deeper for roots and perennials.
Filling it
A roughly even blend of quality topsoil and compost makes a rich, well-draining mix. The soil will settle over the first season, so top it up with compost each spring. You do not need to buy special products; good compost and good topsoil are enough.
Plant by the square foot
Square-foot gardening divides the bed into a one-foot grid and assigns a number of plants to each square based on their spacing. One tomato per square, four lettuces, sixteen carrots, and so on. It keeps spacing simple and a small bed surprisingly productive. Dibble's bed planner does this for you: drag a crop into a square and it lays out the grid, using the same spacing data shown on every crop page.