Proper fertilization is another important key to successful vegetable gardening. The amount of fertilizer needed depends upon soil type and crops. All soils vary, from deep blow sands to fertile, well-drained soils to heavy, dark clays underlaid by layers of rock. Crops grown on sandy soils usually respond to liberal amounts of potassium, whereas crops grown on clay soils do not. Heavy clay soils can be fertilized considerably more heavily at planting than can sandy soils. Heavy clay soils and those high in organic matter can safely absorb and store fertilizer at three to four times the rate of andy soils.
Poor, thin, sandy soils, which need fertilizer the most, unfortunately cannot be fed as heavily and still maintain plant safety. The solution is to feed poor, thin soils more often and in lighter doses. In general, if your garden is located on deep, sandy soil, apply a complete pre-plant fertilizer such as 5-10-10 or 6-12-12 at the rate of 1 to 2 pounds per 100 square feet. If your garden consists of a soil type with a high percentage of clay, a fertilizer such as 10-20-10 or 12-24-12 at 1 to 2 pounds per 100 square feet should be suitable.
Apply the fertilizer a few days before planting. Spade the garden plot, spread the fertilizer by hand or with a fertilizer distributor, and then work the soil one or two times to properly mix the fertilizer with the soil. After the fertilizer is well mixed with the soil, bed the garden into rows in preparation for planting. On alkaline soils, apply 1-20-0 (superphosphate) directly beneath the intended seed row or plant row before planting. Apply the superphosphate 2 to 4 inches beneath the seed or roots of the plant at the rate of 1 to 2 pounds per 100 linear feet of row.
Take care to avoid banding nitrogen material directly beneath the row. Death of the seed or severe burning of the plants could result. Apply additional nitrogen as a furrow or sidedress application (in a row alongside the row of plants) later in the season. For most soils, 2 pounds of 21-0-0 (ammonium sulfate) per 100 linear feet of row, applied in the furrow and watered in, is adequate. Apply at first fruit set for crops such as tomatoes, peppers, and squash. Sidedress leafy crops such as cabbage and lettuce when they develop several sets of first leaves after germination.