Get a kit from your local Co-Operative Extension Service who will explain how to properly dig a sample and package it for mailing. Many soil tests will recommend liming. You may also be advised to add nitrogen, because it's almost always in short supply. Other nutrient deficiencies will be listed along with recommendations for correcting them. When it comes to buying a fertilizer or soil amendment, you have many choices.
Some fertilizers break down slowly, providing a continuous source of nutrients.
Examples are cottonseed meal, blood meal, bone meal, gypsum, Osmocote and ureaformaldehyde. Other fertilizers like ammonium sulfate, potassium sulfate and urea act more quickly, breaking down within weeks. Each fertilizer contains different combinations of nutrients in various quantities, so be sure to read the label carefully before buying. As spring approaches, your garden is primed for a dose of nutrients. March is an ideal month to fertilize plants before new growth begins.