Straight compost usually isn't used as a growing medium, but mixed with soil or other media it works wonders. Compost serves several purposes that make it appealing to vegetable gardeners: It improves soil structure, fertility and water-holding capacity. For the desired results, compost must be finished and cured before application. Unfinished compost can retard vegetable germination and seedling growth or it can compete with growing vegetable plants for existing soil nitrogen, according to the University of Illinois Extension.
Test the compost's maturity to determine if it is ready to use. Fill two flowerpots with compost. Scatter about 12 radish seeds in each pot (count them exactly). Cover the seeds with ¼ of an inch of compost. Water the seeds. If nine or more seeds grow radishes, the compost is ready for use in the vegetable garden.
Cover the garden plot with a 2- to 3-inch layer of compost in the spring. Till the soil to a depth of about 4 inches to work in the compost. Dig and turn the soil by hand or garden tiller. Mix 30 percent compost (by volume) with vermiculite or perlite for growing vegetables in containers.
Plant the desired vegetable seeds or seedlings.
Apply an additional 1 inch of compost to the garden after harvesting the vegetables, if further soil amendment is desired.