These 10 fertilizers come from natural sources and can help improve the fertility of your soil and the nutrition of your crops. Before you add a fertilizer—natural or otherwise—to your garden bed, it’s advised that you have your soil tested for nutrient levels and pH.
It’s especially important to know the pH level before adding phosphorous fertilizers because phosphorous is only available at a fairly limited pH range. Adding more phosphorous to an area with the wrong pH will tie up the nutrient in the soil and not make it available to the plants. Not too mention, excessive nutrients can add to run-off problems and create pollution issues.
If you’re an organic farmer, be sure the fertilizer brands you use are on the Organic Materials Review Institute’s approved materials list. However, for home gardeners or small-scale farmers who aren’t certified organic but want to use only natural fertilizers, all of the following fertilizers are considered organic, even if the particular brand you use isn’t on the list.
1. Fish emulsion and hydrolyzed liquid fish
Processing fish or fish byproducts with heat or acid treatments creates fish emulsion. Fish emulsion is generally a pretty stinky fertilizer, but it’s a good source of all three macronutrients—nitrogen, phosphorus and potassium—with an N-P-K (nitrogen-phosphorus-potassium) ratio of 5-2-2.
Hydrolyzed liquid fish fertilizers are created using enzymes rather than heat. The resulting product is not smelly and retains more trace nutrients and vitamins. The average N-P-K ratio for hydrolyzed fish fertilizers is 4-2-2.
2. Bone meal
A byproduct of slaughtering facilities, bone meal is created through the steam processing and pulverization of animal bones. Bone meal is an excellent high-phosphorus fertilizer with an average N-P-K ratio of 3-15-0. The phosphorous in bone meal takes a few months to become available to plants via microbial processes in the soil. It also contains calcium, another essential plant nutrient. Phosphorous is most available in soil with pH between 6.0 and 7.0, so be sure to test and adjust soil pH if necessary.
Both commercially produced compost and homemade compost benefit soil by adding organic matter, providing food for beneficial microbial life, increasing the soil’s water-holding capacity and gradually releasing plant nutrients. Composts made with high amounts of manure or biosolids (sewage sludge) may be high in salts and can burn plants, but composts made with primarily plant residues do not generally contain troublesome amounts of salt. A typical N-P-K ratio for compost is 2-1-1, though its exact nutritional content depends on many factors. Compost that smells like ammonia or is not yet fully decomposed should be allowed to finish breaking down to avoid damaging plants. Compost also contains many micronutrients essential for plant growth.
The nutrient content of manure is dependent on many factors, including its age, source and the presence of bedding materials. Because of potential pathogen exposure, raw manure should be avoided. Manure should be a minimum of 180 days old or fully composted before it’s added to growing areas. In addition to containing macronutrients, manure is also a great source of several trace nutrients essential for plant growth.
Most cattle and horse manures have an average N-P-K ratio of 1-0.5-0.5 while poultry manures tend to be better high-nitrogen fertilizers (3-1-1 on average). The nutrients in manure are not immediately available to plants and can take up to several years to be released by soil microbes. In general, about half of the total nitrogen is available the first year, with the rest being released slowly over several subsequent seasons. Manure is also an excellent source of organic matter but can contain weed seeds.
5. Rock phosphate
A mineral rock powder, rock phosphate is an excellent source of phosphorous, with an N-P-K ratio of 0-2-0. The phosphorous contained in rock phosphate becomes more available the second year after application, and phosphorous is most available within the soil when the pH ranges between 6.0 and 7.0. Be sure to test soil pH before adding rock phosphate. It is also a good source of calcium.
6. Cottonseed meal
Cottonseed meal is a high-nitrogen fertilizer with an average N-P-K ratio of 6-0.4-1.5. It takes several months to be processed by soil microbes and broken down so that it can release the nutrients it contains. Organic farmers should seek out organic cottonseed meal because cotton is often a genetically modified crop and many pesticides are used during its growth.
7. Alfalfa meal
With an average N-P-K ratio of 2-1-2, alfalfa meal provides plants not only with these macronutrients but also many trace nutrients. It takes one to four months to be broken down by the soil microbes and for the nutrients to become available.
8. Blood meal
A byproduct of slaughtering facilities, blood meal is a very high-nitrogen fertilizer with an N-P-K ratio of 12-0-0. Because of its high ammonia content, inappropriate use or over-fertilizing could cause burned foliage.
9. Feather meal
Although it takes four months or longer to break down and release its nutrients, feather meal is a great high-nitrogen fertilizer with an N-P-K ratio between 7-0-0 and 12-0-0. It is a byproduct of poultry processing.
10. Liquid kelp
Although the amounts of nitrogen, phosphorous and potassium contained in liquid kelp are minimal, it is high in essential trace nutrients as well as plant growth hormones that accelerate plant growth and improve flowering. Liquid kelp is created through the cold processing of this ocean plant. It is mixed with water and applied to plants both as a soil drench and a foliar spray. The nutrients it contains are available immediately for plant use.