You can prepare the soil for the garden anytime of year, but fall is the best time in most regions. The fallow months of winter allow time for the soil amendments, microorganisms, and the wind and rain to transform the soil before the growing season begins.
If you intend to dig the bed in the fall, plant a cover crop such as clover in the late summer and rototill it into the ground before it goes to seed. Or plant a cold-resistant cover crop such as rye and turn it under in spring, three to four weeks before you plan to plant. In regions with very cold winters, turn under cover crops before the ground freezes. In warmer climates turn them under in late fall, or grow them over the winter and turn under in spring.
Here are the steps to making a simple raised-bed garden:
- Begin by taking some soil samples from the area to chose for a vegetable garden and having them analyzed. If you haven’t had the soil tested before, use a soil laboratory. You’ll get a lot of information abaout your soil. If you already know your soil, just test the pH.
- Outline the bed with markers or a long garden hose. If the bed is to be a traditional row-crop garden, make it a rectangle with straight sides. If it is to be a decorative wide-row bed, or a decorative garden with flowers and vegetables, shape it with lazy S’s and gentle sweeping curves.
- If the area is in sod, strip it off and use it elsewhere or compost it.
- If the area is weedy, water it, then treating the existing weeds with weed killer. Weed killer breaks down in the soil in a few days and has no effect on the vegetables to follow. Repeat the process in 10 days to germinate and kill any weed seeds in the soil. Wait another 10 days before continuing. For more information, see Controlling Weeds in New Gardens.
- Now adjust the pH of the soil, determined by the results of your soil test. Optimum soil pH for most vegetables is slightly acid, in the 5.5 to 6.5 range. If your soil is above pH 6.5, apply soil sulfur or iron sulfate. If the soil is below pH 5.5, spread finely ground limestone. See Soil pH for more information.
- Cover the bed with 4 inches of organic material. Use decomposed bark, compost, leaf mold, sphagnum peat moss, decomposed manure, composted sewage sludge (which is dry and relatively odorless), or a combination of any of these. Seaweed is wonderful where it is available.
- Use a rotary tiller to churn it all into the soil. Just hang on while the tiller pulls ahead, tearing up and turning the soil. Owning a tiller is not necessary because garden centers and hardware stores rent rotary tillers at reasonable rates. The easiest to operate are tillers with large wheels. If the soil is heavy and hard to dig, rent the largest tiller you can find. The weight and power make the job easier.
- Shape the beds by digging the paths 4 inches deep and throwing the soil onto the beds. Flatten the top and slope the sides.
- When you are ready to sow the seeds, rake the bed smooth and discard any rocks, sticks, clods, or other debris.
- Spread fertilizer according to label directions. Use a slow-release or organic formulation to last all summer. Rake the fertilizer into the soil and water it in, and you’re ready to plant.