Building a vegetable garden is best begun in fall, but you will have success beginning in spring. Most of the hard work needed to build a vegetable garden is in preparing the soil. Once you've completed this part, maintaining the soil fertility can be achieved by planting a cover crop in fall and incorporating compost into the soil in spring.
Pick the site to build your vegetable garden. It should get a minimum of six hours of sun a day, but 8- to 12-hours of sun is even better. The soil should be well drained, and no puddles should remain in the location after rainfall. Ideally you should locate the vegetable garden near your house for easier access. Good air circulation in the area is important but avoid excessively windy locations because heavy winds can damage or break plants.
Improve the soil. Ideally you should begin this step in autumn of the year before you plant the vegetable garden, but a garden can be successfully started in spring. Begin by removing any vegetation, debris and large rocks. Lay down a minimum of 2 inches of peat moss and 2 inches of garden compost. If available, add a 2-inch layer of well-rotted manure. Turn the soil over with a garden shovel or by rototilling to loosen the soil, and incorporate the soil improvements. Rake the area smooth when finished.
Plant a cover crop if beginning in fall; omit this step if beginning in spring. Cover crops will add further organic material and help improve the soil. Sow oats, clover or winter rye. Broadcast the seed over the garden. After the plants have grown for 3- to 4-weeks, till them into the soil with a rototiller or turn under with a garden shovel. They will break down over the winter.
Turn the soil over one more time before planting in spring. You may only need a shovel and not a rototiller, but you can use a rototiller if desired.
Make a scale drawing of your vegetable garden. Determine the mature heights of the vegetables you will grow from the seed catalog or package. Plant taller vegetables on the north side of the plot so they do not shade the shorter varieties of vegetables. Vines such as cucumber and squash can grow up a trellis on the north side of the plot. Tomatoes and corn and other tall vegetables should be planted on the north side. Medium-size vegetables such as cabbage, broccoli, peppers and eggplant should be planted in the center of the plot. Smaller vegetables include carrots, onions, lettuce, salad greens and herbs, and should be planted at the southern edge, so they will not be shaded by the taller vegetables.
Consider encircling your vegetable garden with a small mesh fence to keep animals out. This can serve double duty; plant cucumbers, squash or melons along the fence on the north side of the plot and let them climb up it. This will also give you more space to grow other crops because vines take up a lot of room when allowed to ramble across the ground.
Apply a 3- to 6-inch layer of organic mulch to the garden after your crops are planted and the seeds have germinated. The mulch will help keep the moisture in the soil, reducing the need for watering and will also suppress most of the weeds. Those that do grow will be spindly and easily pulled. Organic mulch will contribute its organic matter to the soil as it decomposes and help prevent erosion from wind or rain.