Organic Fertilizers

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Terms

By legal definition, the term fertilizer refers to a soil amendment that guarantees the minimum percentages of nutrients (at least the minimum percentage of nitrogen, phosphate, and potash).

An organic fertilizer refers to a soil amendment derived from natural sources that guarantees, at least, the minimum percentages of nitrogen, phosphate, and potash.  Examples include plant and animal by-products, rock powders, seaweed, inoculants, and conditioners.  These are often available at garden centers and through horticultural supply companies. 

These should not be confused with substances approved for use with the USDA National Organic Program (NOP).  The USDA NOP, with its “USDA Organic” label, allows for the use of only certain substances.  The Organic Materials Review Institute (OMRI  at www.omri.org) approves brand name products made with ingredients from the “National List” for use with the NOP.  (For details refer to www.ams.usda.gov/nop and click “NOP Regulations” and then “National List Information”).  Many of the organic fertilizers listed here will meet NOP standards (based on the National List).  Growers participating in the NOP should consult with their certifier to ensure compliance for organic certification.

The terms soil amendment refers to any material mixed into the soil.  Mulch refers to a material placed on the soil surface.  By legal definition, soil amendments make no legal claims about nutrient content or other helpful (or harmful) effects it will have on the soil and plant growth.  In Colorado, the term compost is also unregulated, and could refer to any soil amendment regardless of active microorganism activity. 

Many gardeners apply organic soil amendments, such as compost or manure, which most often do not meet the legal requirements as a “fertilizer” but add small amounts of nutrients.

Notes:

  • Release Time – Organic products require the activity of soil microorganisms before nutrients are available for plant uptake.  Microorganism activity is generally dependant on soil temperatures greater than 50°F in the presence of sufficient soil moisture.  Dry and/or cold soil conditions will delay the release of nutrients from these organic sources.  This period refers to how long these products are available if applied to the soil.  Use this information to time the application of the product.
  • Application – Different products may be applied in various ways.  Some may be tilled in (worked into the soil with a machine or hand tool), others may be applied as a foliar spray (mixed with a surfactant and sprayed in a fine mist on the leaf surface while temperatures are below 80°F), and some may be injected into a drip or overhead irrigation system (fertigation with a siphon mixer).  Application rates in this fact sheet are generalized and based on some manufacturers’ recommendations.  Over- or under-fertilization may occur using these recommendations.

Plant By-Products

Alfalfa Meal or Pellets

Alfalfa meal or pellets are often used as animal feed.  Primarily they are used to increase organic matter in the soil but do offer nutrients and a high availability of trace minerals.  They contain trianconatol, a natural fatty-acid growth stimulant.

Alfalfa Meal or Pellets
Typical NPK analysis
2-1-2
Release time
1-4 months
Pros
Available at feed stores
Cons
May contain seeds
Application
Till in 2-5 pounds per 100 square feet


Corn Gluten Meal

Corn gluten meal materials have a high percentage of nitrogen.  It carries a warning to allow 1 to 4 months of decomposition in the soil prior to seeding.  Allelopathic properties will inhibit the germination of seeds.  However, there is no danger to established or transplanted plants.  This product is also marketed as a pre-emergent weed control for annual grasses in bluegrass lawns.

Corn Gluten Meal
Typical NPK analysis
9-0-0
Release time
1-4 months
Pros
Very high nitrogen
Cons
Germination inhibitor, some are GMOs
Application
Till in 20-40 pounds per 1000 square feet


Cottonseed Meal

Cottonseed meal is a rich source of nitrogen.  Buyers should be aware that many pesticides are applied to cotton crops and residues tend to remain in the seeds.  Pesticide-free cottonseed meal is available. 

Cottonseed Meal
Typical NPK analysis
6-0.4-1.5
Release time
1-4 months
Pros
High nitrogen
Cons
Pesticide residues
Most are GMOs
Application
Till in 10 pounds per 100 square feet


Soybean Meal

Used primarily as an animal feed product.  Available bagged at many feed stores.

Soybean Meal
Typical NPK analysis
7-2-1
Release time
1-4 months
Pros

High nitrogen
Available at feed stores

Cons
Almost half of the conventionally grown soy is GMO.
Application
8 pounds per 100 square feet


Animal By-Products

Bat Guano – High N

Bat guano (feces) harvested from caves is powdered.  It can be applied directly to the soil or made into a tea and applied as a foliar spray or injected into an irrigation system.

Bat Guano – High N

Typical NPK analysis
10-3-1
Release time
4+ months
Pros
Stimulates soil microbes
Cons
Cost
Application
Till in 5 pounds per 100 square feet or as a tea at 3 teaspoons per gallon of water


Bat Guano – High P

Bat guano (feces) harvested from caves is powdered.  It can be applied directly to the soil or made into a tea and applied as a foliar spray or injected into an irrigation system. The difference is that it is processed for high phosphorus content.

Bat Guano – High P
Typical NPK analysis
3-10-1
Release time
4+ months
Pros
Stimulates soil microbes
Cons
Cost
Application
Till in 5 pounds per 100 square feet or as tea at 3 teaspoons per gallon of water


Blood Meal

Blood meal, made from dried slaughterhouse waste, is one of the highest non-synthetic sources of nitrogen.  If over-applied it can burn plants with excessive ammonia.

Blood Meal
Typical NPK analysis
12-0-0
Release time
1–4 months
Pros
Available at feed stores
Cons
Can burn.
Expensive at garden centers
Application
Till in 5–10 pounds per 100 square feet


Bone Meal

A well-known source of phosphorus, bone meal is steam processed and widely available at feed stores and in garden centers.  If purchased at feed stores, phosphorus is expressed on the label as elemental phosphorus and is 2.3 times higher than numbers shown on garden center labels for phosphate (i.e. – 12% phosphate is the same as 27% phosphorus).  However, recent CSU research has shown that phosphorus from bone meal is only available to plants in soils that have a pH below 7.0.

Bone Meal
Typical NPK analysis
3-15-0
Release time
1–4 months
Pros
Highly plant available form of phosphorus
Cons
Cost  
Application
Till in 10 pounds per 100 square feet


Feather Meal

Sourced from poultry slaughter, feather meal has fairly high nitrogen levels but is slow to release the nitrogen.

Feather Meal
Typical NPK analysis
N varies 7 – 12% on process
Release time
4+ months
Pros
Long term fertilizer
Cons
Cost versus speed of nitrogen release
Application
Till in 2.5-5 pounds per 100 square feet


Fish Emulsion

Infamous for its foul smell, emulsions are soluble, liquid fertilizers that have been heat and acid processed from fish waste. 

Fish Emulsion
Typical NPK analysis
5-2-2
Release time
1 – 4 months
Pros
Adds micronutrients
Cons
Some have foul smell.
Application
Mix 6 tablespoons per gallon of water


Enzymatically Digested Hydrolyzed Liquid Fish

Enzymatically digested hydrolyzed liquid fish uses enzymes to digest the nutrients from fish wastes instead of using heat and acids.  This retains more of the proteins, enzymes, vitamins and micronutrients than emulsions.

Enzymatically Digested Hydrolyzed Liquid Fish

Typical NPK analysis
4-2-2
Release time
1 – 4 months
Pros
More nutrients than emulsions
Cons
More expensive than emulsions
Application
Mix 5 tablespoons per gallon of water


Fish Meal

Fish meal is ground and heat dried fish waste.

Fish Meal
Typical NPK analysis
10-6-2
Release time
1 – 4 months
Pros
Nitrogen and phosphorus source
Cons
Heat processed
Application
Till in 5-10 pounds per 100 square feet


Fish Powder

Fish power is dried with heat and turned into water-soluble powder.  It is a high source of nitrogen.  Many can be mixed into solution and injected into an irrigation system.

Fish Powders
Typical NPK analysis
12-0.25-1
Release time
Immediate to 1 month
Pros
Adds micronutrients
Cons
Heat processed
Application
Till in 1-2 ounces per 100 square feet


Compost, Manure, and Biosolid Based Products

For information on biosolids, worm casting, manure, and compost, refer to the following CMG GardenNotes:


Rock Powders

Rock powders relevant for use in Colorado soils are those that supply phosphorus.  Those that serve as a potassium source (greensand, feldspar, potassium sulfate, biotite, etc.) are not necessary as Colorado soils are naturally high in potassium.  Similarly, it is not necessary to add calcium (gypsum, lime, etc.) due to naturally high calcium levels in Colorado soils and arid conditions.

If you are making annual applications of manure and/or compost to your garden to add nitrogen, you should have sufficient levels of phosphorus in your soil.  If you are applying manure or compost to your garden based on phosphorus needs, you might have an excess N supply.  Excess nitrogen can lead to poor flower/fruit development and increases water pollution potential from nitrogen leaching from the soil.

Generally, plant or animal sources are the best value for phosphorus in the home garden.  Recent CSU research results concluded that no rock P (regardless of mesh size) is available for plant use unless the soil pH is below 7.0.

Colloidal Phosphate – a.k.a. Soft Rock Phosphate

This product is made by surrounding clay particles with natural phosphate.  Total phosphate is about 20% while available phosphate is about 2-3%.  This is why you can apply large amounts of colloidal phosphate, as it will release slowly over the years (usually more available the second year than the first).  For home gardeners the cost/return is adequate to apply colloidal phosphate at rates to supply phosphorus for this season’s crops.  This product also adds micronutrients to soil.

Micronized (passing through 1000 mesh screen [1000 wires per square inch]) sources may be more available than regular soft rock grinds in soils with a pH below 7.0.

Seaweed

Kelp is the most common form and is valued not for its macronutrient (nitrogen, phosphorus and potassium) contributions but for micronutrients.

Kelp is often mixed with fish products to enhance growth.

Three processes are available:  extracts (as kelp meal or powder), cold-processed (usually liquid) and enzymatically digested (liquid).  Ranked in quality of content and plant availability they are (highest to lowest) 1) enzymatically digested, 2) cold-processed and 3) extracts.

Kelp Meal

Kelp meal, a product of the ocean, is used primarily as a trace mineral source.  It is often combined with fish meal to add nitrogen, phosphorus, and potassium.

Kelp Meal
Typical NPK analysis
negligible
Release time
4+ months
Pros
Adds micronutrients
Cons
Insignificant nitrogen, phosphorus, and potassium
Application
Till in 1 pound per 100 square feet


Kelp Powder

Kelp powder is similar to kelp meal but ground fine enough to put into solution and applied as a foliar spray or injected into an irrigation system.

Kelp Powder
Typical NPK analysis
1-0-4
Release time
Immediate – 1 month
Pros
Adds micronutrients
Cons
Insignificant nitrogen, phosphorus, and potassium
Application
Mix ¼ to ½ teaspoon per gallon of water


Liquid Kelp

Usually cold processed, liquid kelp will have higher levels of growth hormones than extracts.  Some may also be enzymatically digested, making the growth hormones even more available to the plants.

Liquid Kelp
Typical NPK analysis
Negligible
Release time
Immediate – 1 month
Pros
Adds micronutrients
Cons
Insignificant nitrogen, phosphorus, and potassium
Application
Mix 1 – 2 tablespoons per gallon of water



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Authors: Adrian Card, with David Whiting and Carl Wilson (CSU Extension), and Jean Reeder, Ph.D. (USDA-ARS, retired).

  • CMG GardenNotes are available online at www.cmg.colostate.edu
  • Colorado Master Gardener/Colorado Gardener Certificate Training is made possible by a grant from the Colorado Garden Show, Inc.
  • Colorado State University, U.S. Department of Agriculture, and Colorado counties cooperating
  • Extension programs are available to all without discrimination.
  • Colorado Master Gardener LogoNo endorsements of products mentioned is intended nor is criticism implied of products not mentioned.
  • Copyright. 2011. Colorado Master Gardener Program, Colorado State University Extension. All Rights Reserved. CMG GardenNotes may be reproduced without change or additions, for nonprofit educational use.

Revised December 2011

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