What Are Useful Alternatives to Inorganic Fertilizers?

Soil Amendments

• Soil amendments, such as manure and compost, are not technically called fertilizers because they aren't regulated and can vary in their nutrient content, according to Colorado State University. However, they are useful additives to the garden because they improve soil texture and drainage and can add nutrients and microorganisms to the soil. Use only well-rotted manure and compost to reduce the risk of soilborne pathogens. Apply manures two to three months before a vegetable crop is set for harvest.

Plant By-Products

• Several fertilizers made from plant by-products, such as corn gluten meal, alfalfa pellets, cottonseed meal and soybean meal, are rich in nitrogen and have trace levels of minerals. Corn gluten meal, which is more expensive than synthetic fertilizers, suppresses the germination of seeds; use it three to four months before seeding, or after plants have germinated. Alfalfa pellets are used to increase organic matter in the soil and offer nutrients, but can contain seeds. Cotton is heavily treated with pesticides and residue tends to remain in the seeds. Soybean meal, like the other by-products, can contain GMOs (genetically modified organisms).

Animal By-Products

• Animal by-products generally are obtained from the slaughterhouse and fishing industries and provide high levels of nutrients to plants. Bone meal, blood meal, feather meal and fish emulsions are used as alternatives to synthetic fertilizers. The main drawback of most of these products is cost, although they usually cost less at feed stores than nurseries. Most animal by-products release nutrients slowly, although blood meal may burn plants if applied to closely to the roots. Some of these products may have a foul smell that dissipates within a few days of application.

Cover Crops

• Vegetable gardening is hard on soil. Replenish your soil during the winter by planting a cover crop, such as clover, winter wheat or winter rye. These plants prevent erosion and weed growth, reduce soil compaction and add nitrogen to the soil when they are dug under in the spring. Choose a cover crop based on its adaptability to your area and the availability of seed. Plants that overwinter, such as perennial rye grass and winter rye produce heavy top growth in the spring that is more difficult to dig under.