Best Organic Fertilizers

Feed your garden by choosing natural soil amendments that are rich in nutrients, minerals, and organic matter — not just nitrogen.

  • Organic fertilizers are naturally slow-releasing and provide nutrients to plants where they need it.
    Photo by iStock/cjp
  • Bat guano is a natural all-purpose fertilizer containing nitrogen and lots of trace elements.
    Photo by iStock/sasimoto
  • Earthworm castings contain many trace minerals and are gentle, sweet-smelling, and clean.
    Photo by iStock/zerocattle
  • Compost is the key to any organic program, and can easily be made from food scraps.
    Photo by Terry Wild Stock
  • Manure from rabbits is a terrific natural fertilizer.
    Photo by Fotolia/awgeo
  • Llama and alpaca manure can be applied directly to plants without first being composted.
    Photo by iStock/Terraxplorer

Organic growing techniques have been practiced for as long as humans have tilled the earth. Only since World War II has agriculture become dependent upon toxic synthetic fertilizers and pesticides. These man-made chemicals temporarily increased the yield of many crops, but also increased the long-term cost of production, caused air and water pollution, changed soil structure, and jarred the entire ecosystem.

Organic fertilizers, whether they’re meals, manures, or composted plant material, contain N-P-K (nitrogen-phosphorus-potassium), trace minerals, enzymes, vitamins, and lots of organic matter. Of those ingredients, 100 percent are useful to the soil and plants. In contrast, synthetic fertilizers contain no organic matter. Soil microorganisms must have this carbon energy source, and, if it isn’t provided, the microbes will take it from the soil. That drains soil health with every fertilizer application.

Unlike synthetic fertilizers, organic fertilizers don’t create high levels of salts, such as nitrates, which disturb or even kill beneficial soil organisms. Organic fertilizers release nutrients slowly and naturally. (See my chart, Best Natural Organic Fertilizers, for a rundown.) All components are usable by the plants, because organic fertilizers don’t contain useless fillers as with synthetic fertilizers.

Feeding the soil and plants with nothing but N-P-K is like feeding your kids nothing but soda. Soil and people need a balance of nutrients. For some unknown reason, fertilizer recommendations continue to emphasize these three nutrients with special emphasis on high levels of nitrogen. Studies have shown that 80 percent or more of all synthetic nitrogen applied to the soil will be volatized or leached out, and the 10 to 20 percent that does reach the plant will be harmful. Other studies show that an excess of chemical fertilizer slows or even stops the activity of microflora and microfauna, such as beneficial bacteria, algae, fungi, and other microorganisms. Harsh fertilizers also cause damage to macroorganisms, such as earthworms, millipedes, and centipedes, which are extremely important to the natural processes in the soil.

The most important material in an organic garden is organic matter that becomes humus during the decomposition process. Humus becomes humic acid, other beneficial acids, and mineral nutrients. Organic fertilizers are better than artificial products because they’re the derivatives of plants and animals and therefore contain most or all the trace elements that exist in growing plants and animals. In addition, organic fertilizers are naturally slow-releasing and provide nutrients to plants when they need it. Synthetic fertilizers glut the plants with nutrients immediately after application, which is usually at the wrong time.

Here are my recommendations for the best, natural, organic fertilizers to boost your garden’s production and build soil health. This chart summarizes the N-P-K ratio and the benefits of most of these soil-boosting amendments.



Fall 2021!

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