Most vegetables grow well in full sun and loamy, well-drained soil. Unfortunately, many gardeners must work with clay soil when trying to establish a vegetable garden. Clay soil is composed of fine dirt particles that compact together and has very little air space between the particles. Because of this, clay soil will not drain very well. Fortunately, clay soil is full of nutrients because water cannot carry them away. Unfortunately, clay is slippery when wet and rock hard when it dries. The best way to grow vegetables in clay soil is to incorporate organic materials into the soil to improve drainage and structure.
Take a sample of your soil by digging 1 quart of soil from between 6 and 10 locations across your garden. Mix the soil completely and spread it over a newspaper to dry. Place 1 cup of the mixed soil in a sandwich bag and take it to a soil laboratory for testing. A soil test can determine the pH of soil as well as the soil's clay content ratio and nutrient deficiencies. The test results will make recommendations on what amendments to add to the soil as well as application rates. Return the rest of the soil to your garden.
Break up your garden in fall to a depth of 12 inches using a rototiller. The combination of freezing and thawing over the winter will help to loosen clay soil to make it easier to prepare a planting bed in the spring.
Add soil amendment to your soil based on the results of your soil test in spring to change the soil structure of clay soil. Common amendments to improve clay soil include organic material to aerate the soil and improve drainage. Good examples are wood chips, compost, composted manure, sawdust and peat moss. Spread these amendments over your soil in a 4-inch layer. Mix the amendments into the soil with a rototiller.
Dig planting holes for your vegetable transplants or drill holes and furrows for vegetable seed. Place transplants into their holes and put seeds into drill holes or furrows at a depth that is twice the diameter of the seed at its widest point. Cover with soil and water so that the soil remains only as damp as a wrung-out sponge.
Mulch around sprouted seedlings and transplants with straw to help hold in moisture and choke out grass weeds.