Natural Fertilizers - Plant Based

Natural fertilizers and amendments come from many sources and thus are quite variable. Some come with potential ethical and or environmental issues and so due diligence is always important when choosing a product that will both address your issues and comply with your values. Needs should be based on a comprehensive, accurate soil test. This can save time, money, and frustration in the future. Many products are blends of these and other ingredients that may or may not me defined as organic. Always read the labels!

Here is some basic information about some commonly available plant-derived fertilizers. See the table at the end of this article for details on nutrient composition and availability.

• Made from the alfalfa. Plants are harvested, dried, and pelletized for easy distribution.
• Contains good amounts of N-P-K, as well as has a large suite of trace elements and a high proportion of organic matter.
• Naturally contains a plant growth stimulant called triacontanol, which has been shown to improve plant growth, vigour, and yields.
• Availability depends on local industry. Here in Saskatchewan, we have ample access to high quality, locally grown alfalfa meal (lucky us!).

• Made from dried and ground seaweed and kelp. The two species commonly used are Ascophyllum nodosum and Macrocystis integrifolia.
• Contain nutrients in varying levels depending on source and species, most notably potassium (K) and a large amount of trace elements. Are immediately available to the plant.
• Also contain plant growth hormones that can be beneficial to plant growth and development.
• Care must be taken to ensure that the product has been sustainably harvested.

• Source of potassium, some phosphorus and trace elements, depending on type of wood burned. Has been used since the olden days. The term “potash” is derived from the method of processing wood ash.
• Very alkaline (high pH) so should be used sparingly in soils with elevated pH. Saskatchewan soils south of the Boreal Forest tend to be neutral to slightly alkaline in pH.
• Free for those with a fireplace or fire pit. Ensure you do not use ash from the burning of treated wood as harmful residues may remain.

• Varying levels of N-P-K depending on source. Some are complete, some are not
• Contain high levels of organic matter.
• Often difficult to source unless local industry exists.
• Can contain pesticide residues, harm young seedlings (corn gluten meal), and can contain genetically modified organisms (GMOs). Know your source!

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Table 1. List of organic fertilizers and amendments with typical nutrient content and nutrient availability. Information adapted from product labels, Teaming With Nutrients (Lowenfels, 2013), and Whalen et al. (2020).

Fertilizer Type	Nitrogen (N)%	Phosphorus (P) %	Potassium (K) %	Trace Elements	Nutrient Availability*
Animal-Derived
Blood Meal	12	0	0	+	Fast
Bone Meal	2-4	10-15	0	+	Medium
Fish Bone Meal	4	13	0	++	Medium - Fast
Fish Emulsion	5	2	2	+++	Fast
Fish Hydrolysate	2-4	2-4	0.5-2	+++	Medium - Fast
Insect Frass (Cricket, Mealworm, Black Soldier Fly)	3-7	2-3	2	+++	Fast
Feather Meal	7-12	0	0	+	Medium - Slow
Crab/Shrimp Meals	2-5	3-8	0-15	++	Medium - Slow
Cattle Manure	0-1	0-1	0-1	++	Medium
Chicken Manure	5	3	2	++	Medium - Fast
Rabbit Manure	0-1	0-1	0-1	++	Medium
Wool Pellets	10	0	2	+	Medium - Slow
Bat Guano	3-10	3-10	1	++	Fast
Plant Derived
Alfalfa Meal	3	0-1	2-3	+++	Medium - Fast
Kelp/Seaweed (Liquid)	0	0	3	+++	Fast
Kelp/Seaweed (Powder)	0	0	17	+++	Fast
Other plant meals (corn, soy, cotton)	7	2	1	+	Medium
Wood Ash	0	1	3	++	Medium - Fast
Mined Product
Garden lime (CaCO3)	0	0	0	+	Slow
Dolomitic Lime (MgCaCO3)	0	0	0	+	Slow
Gypsum (CaSO4)	0	0	0	+	Medium - Slow
Rock Phosphate (Soft/Colloidal)	0	2.5 - 13	0-1	+	Slow
Rock Dusts (Basalt, glacial)	0	0	0-1	++	Slow
Wollastonite (CaSiO3)	0	0	0	+	Slow
Sulfate of Potash**	0	0	50	N/A	Medium
Epsom Salts (MgSO4)**	0	0	0	N/A	Fast
Azomite	0	0	0	+++	Slow
Diatomaceous Earth	0	0	0	++	Slow
Greensand/Zeolite	0	0	0	++	Slow
Other Amendments
Compost	Variable	Variable	Variable	Variable	Medium - Slow
Compost Teas	Variable	Variable	Variable	Variable	Medium - Fast
Worm Castings	Variable	Variable	Variable	+++	Medium - Fast
Perlite	0	0	0	N/A	N/A
Vermiculite	0	0	0	+	N/A
Biochar	0	0	0	+	N/A
Mulch	0	0	0	+	N/A

*Nutrient availability greatly depends on surface area of the fertilizer. In general, the finer the texture of the material, the more accessible it is likely to be. Availability is also highly dependent on local soil conditions and microbial activity.

** Mainly produced synthetically but some mines exist.

Albert, S., & Bloem, E. (2025). Antibiotic contamination of fresh organic fertilizers and processed bio-based fertilizer products. Agrosystems, Geosciences & Environment, 8(1). https://doi.org/10.1002/agg2.70059

Beesigamukama, D., Subramanian, S., & Tanga, C. M. (2022). Nutrient quality and maturity status of frass fertilizer from nine edible insects. Scientific Reports, 12(1), 7182. https://doi.org/10.1038/s41598-022-11336-z

Camilli, F., Focacci, M., Prà, A. D., Bortolu, S., Ugolini, F., Vagnoni, E., & Duce, P. (2025). Turning Waste Wool into a Circular Resource: A Review of Eco-Innovative Applications in Agriculture. Agronomy, 15(2), 446. https://doi.org/10.3390/agronomy15020446

Lowenfels, J. (2013). Teaming With Nutrients: The Organic Gardener’s Guide to Optimizing Plant Nutrition. Timber Press.

Marwa, E. M. M., Andrew, T., & Hatibu, A. A. (2021). Challenges facing effective use of bat guano as organic fertilizer in crop production: A review. International Journal of Engineering and Applied Sciences, 8(8), 8–15. https://doi.org/10.31873/IJEAS.8.8.01

Poveda, J. (2021). Insect frass in the development of sustainable agriculture: A review. Agronomy for Sustainable Development, 41(1), 5. https://doi.org/10.1007/s13593-020-00656-x

Sahin, O., Yagcioglu, K. D., Kadioglu, Y. K., Ozturk, H. S., & Gunes, A. (2025). Valorization of sheep wool: Impact of keratin hydrolysate on the growth and mineral nutrition of lettuce, spinach, and radish plants. Journal of Soil Science and Plant Nutrition, 25(2), 2642–2652. https://doi.org/10.1007/s42729-025-02289-z  

Whalen, J. K., Ziadi, N., Schoenau, J. J., Paré, M. C., Burton, D. L., & Bruulsema, T. (2020). Soil nutrient cycling. Digging into Canadian soils: An introduction to soil science. SaskOER. https://www.saskoer.ca/soilscience/chapter/soil-nutrient-cycling/