And a single application may last a whole growing season. You also might choose organic fertilizers for philosophical or environmental reasons. Fertilizers containing high concentrations of nitrogen, when used alone, can actually deplete soil organic matter, so if you use any such fertilizer, apply plenty of bulky organic matter, too. Dig materials such as straw, peat, compost, and leaves into the soil, or lay them on as mulch. Among them are Chilean nitrate, rock phosphate, greensand, and sulfate of potash magnesia.
Synthetic fertilizers do have some advantages.
They cost less, are easier to transport, and more uniform in nutrient content. All but slrelease types are more quickly available to plants than organic fertilizers. Fertilizers are necessary make up for nutrients that are naturally carried down into the groundwater by rainfall, carried off into the air as gases, and carried into the kitchen by you. The only way to know for sure if your garden requires fertilizers is to have the soil tested. The cooperative extension services in most states test garden soil for a nominal fee.