For organic gardeners, creating a living soil rich in humus and nutrients is the key to growing great fruits and vegetables, abundant flowers, and long-lived ornamental trees and shrubs. The overall fertility and viability of the soil, rather than the application of fertilizers as quick fixes, is at the very heart of organic gardening. But like all gardeners, organic gardeners have to start somewhere. Your soil may be deficient in certain nutrients. It may not have excellent soil structure. Its pH may be too high, or too low. Unless you’ve lucked into the perfect soil, you’re going to have to work to make it ideal for gardening.

Chemical Vs. Organic

Many organic materials serve as both fertilizers and soil conditioners they feed both soils and plants. This is one of the most important differences between a chemical approach and an organic approach toward soil care and fertilizing. Soluble chemical fertilizers contain mineral salts that plant roots can absorb quickly. However, these salts do not provide a food source for soil microorganisms and earthworms, and will even repel earthworms because they acidify the soil. Over time, soils treated only with synthetic chemical fertilizers lose organic matter and the all-important living organisms that help to build a quality soil. As soil structure declines and water-holding capacity diminishes, more and more of the chemical fertilizer applied will leach through the soil. In turn, it will take ever-increasing amounts of chemicals to stimulate plant growth. When you use organic fertilizers, you avoid throwing your soil into this kind of crisis condition.

The manufacturing process of most chemical fertilizers depends on nonrenewable resources, such as coal and natural gas. Others are made by treating rock minerals with acids to make them more soluble. Fortunately, there are more and more truly organic fertilizers coming on the market. These products are made from natural plant and animal materials or from mined rock minerals. However, the national standards that define and distinguish organic fertilizers from chemical fertilizers are complicated, so it’s hard to be sure that a commercial fertilizer product labeled “organic” truly contains only safe, natural ingredients. Look for products labeled “natural organic,” “slow release,” and “low analysis.” Be wary of products labeled organic that have an NPK (nitrogen-phosphorus-potassium) ratio that adds up to more than 15. Ask a reputable garden center owner to recommend fertilizer brands that meet organic standards.

If you’re a gardener who’s making the switch from chemical to organic fertilizers, you may be afraid that using organic materials will be more complicated and less convenient than using premixed chemical fertilizers. Not so! Organic fertilizer blends can be just as convenient and effective as blended synthetic fertilizers. You don’t need to custom feed your plants organically unless it’s an activity you enjoy. So while some experts will spread a little blood meal around their tomatoes at planting, and then some bonemeal just when the blossoms are about to pop, most gardeners will be satisfied to make one or two applications of general-purpose organic fertilizer throughout the garden.

Convenient products like dehydrated organic cow-manure pellets and liquid seaweed make it easy to fertilize houseplants and containers too. (Don’t use fish emulsion indoors, though, because of its strong odor. Save it for your outdoor containers and garden plants.)

If you want to try a plant-specific approach to fertilizing, you can use a variety of specialty organic fertilizers that are available from mail-order 231 supply companies or at most well-stocked garden centers and home centers. You can find everything from organic tomato and rose fertilizer mixes to organic fertilizer mixes especially created for transplants, lawns, heavy bloom production, even containers. 

You can also make custom mixes to address your plants’ specific needs. For example, you can use bat and bird guano, composted chicken manure, blood meal, chicken-feather meal, or fish meal as nitrogen sources. Bonemeal is a good source of phosphorus, and kelp or greensand are organic sources of potassium.