My notes on “Organic Fertilizers”.

by Alex Robles

Everyone in the cannabis cultivation industry is scrambling to find the perfect “Organic Fertilizer” that’s state approved and will consistently feed a crop.  All fertilizers have their benefits and limits, so pay attention to what you need.  These are just some of my notes on this topic that I’ve taken from different sources.  This is by no means meant to be a complete list of information on this broad topic.  I didn’t add a lot of NPK rations because every product and nutrient source will be different at different times.  I intentionally left out worm castings because I’m a big fan of it and I feel that deserves it’s own entry.

  • Organic fertilizers are made from animal matter, animal manure and vegetable matter (e.g. compost and crop residues).  Natural organic fertilizers include animal wastes from meat processing, peat, manure, slurry, and guano.

Growers Note: Inorganic fertilizer, also referred to as synthetic fertilizer, because they’re manufactured artificially and contains mineral salts or synthetic chemicals.

  • To be sustainable, one of the things organic farms need, is to be self-sufficient in nitrogen (N).   The fixation of atmospheric dinitrogen (N2) in the soil is helped by legumes, recycling of crop residues (green manures) and the application of animal manure, or compost.  As N is most often the limiting nutrient in organic systems, the aim has to be to maximize N2 fixation within the system.

Growers Note:  Dinitrogen (N2) forms about 78% of Earth’s atmosphere, making it the most abundant uncombined element.  Nitrogen fixation refers to the conversion of atmospheric nitrogen gas (N2) into a form usable by plants and other organisms (ammonia NH).

  • One of the most common types of packaged soil amendments is the manure or compost based blended fertilizer.  Each of these products will typically test at 2 to 5% for each macronutrient (NPK).  Dried compost is used as a bulking agent, nutrients source and organic matter.  It’s typically blended other things rock minerals, plant and animal by-products.
  • Organic manures are basically made from either plant or animal by products.  The plant by products are mainly meals or cakes (cottonseed cake, neem meal), fruit pomaces, leaf compost soybean meal, wood ash etc.  While the animal by-products includes things likes of bone meal, blood meal, feather meal, fish meal and fish emulsion.
  • Organic fertilizers should be a sustained sources of nutrients due to slow releases during decomposition.
  • By increasing soils organic matter, organic farming can help return the natural fertility of damaged soil, which will improve the crop productivity.  Organic fertilizers enhance the natural soil processes, which have long-term effects on soil fertility.
  • All organic fertilizer has a Nitrogen, Phosphoric acid and Potassium amounts labeled as N-P-K ratio number.  This ratio tells the percentage by weight of each of these three elements.

Liquid Fish Fertilizer

There are a few things that limit the use of liquid fish fertilizer in a large farm setting; it is extremely expensive compared to other sources of fertilizer and it doesn’t build soil.  Typically, fish emulsion fertilizers have a ratio of 5 :2:2 or 5:1:1, I’ve used an even 2-2-2 product in the past.

  • Dried fish fertilizer (fish bone meal) is an organic product–for the most part.  It feeds plants, microbes and improves soil structure.
  • Fertilizers that are mostly water based like fish emulsion, hydrolysate and manure tea may provide nutrients immediately, but they’re not a good source for slow release nutrients.  They also don’t build soil structure because they don’t contain any significant organic matter to feed the microbes.
  • Fish emulsion and fish hydrolysate start with the left over bits from the fish industry–the parts no one else wants.  These are then treated with different chemicals and enzymes to break down larger organic molecules into nutrients and other small organic molecules. After that, one of two things is going to happen; it is either heated or cold processed.  Fish emulsion is the end product if the heating process is used.  Fish hydrolysate is the result of using cold processing.
  • In the process of turning fish scraps into fertilizer companies add a number of chemicals, including phosphoric acid, and odor inhibitors.  As long as these ingredients form less than 1% of the finished product, the product can still be called 100% organic.
  • Liquid fish fertilizer is made from whole fish and carcass products, including bones, scales and skin.  These bits are changed into nutrients for the garden.  Different types of fish, such as menhaden and anchovies, are ground into a slurry.

Growers Note: Menhaden is caught in harbors and rivers on the coast and are exposed to coastal pollutants.  Also, lake fish used could contain Mercury and PCB’s.

  • After straining out solids, sulfuric acid is added to lower the pH, preventing microbes from growing.
  • Whatever is left after these processes is then boiled down to a 50% solution and sold as a fertilizer.  Two things to think about when choosing a liquid fish fertilizer.
  1. The steam they use to remove the meal from the fish frame comes from municipal water, which contains chlorine.  When the product is boiled down to a 50% solution, the chlorine is doubled and can be as high as 14% in the final product.
  2. You cannot evaporate a liquid down to a 50% solution without the use of heat.  Once heat is used, all the heat sensitive vitamins, amino acids, growth hormones and the enzymes are destroyed.  Since it has been heated, no matter what the salesperson tries to tell you, the heat sensitive components from the fish are gone.  Some products have enzymes added back into it so companies can call it a hydrolyzed process, but it’s just a hydrolyzed emulsion.
  • Since emulsions have the consistency of syrup, they’re  famous for clogging sprayers and getting stuck in the bottom of holding tanks.
  • Liquid fish fertilizer has about 2% nitrogen, which is the same as most organic fertilizers; compost, manure, and coffee grounds. (Based on a NPK analysis for coffee grounds from the North Carolina State University, the ratio is 2.1:0.3:0.3.).

Animal Manures

Manures should not be used fresh.  First, it needs to age, rot or compost — which turns it into a more flexible fertilizer in the process.  Fresh manure can have dangerous bacteria, such as E. coli, which are destroyed during the composting process.  Aside from that, fresh manure often contains grass and weed seeds that can cause problems in fields and prepared beds when spread.  Finally, the ammonia in fresh manure can cause strange growth patterns and “burn” delicate plant roots.

  • Cow manure helps with moisture retention.  It also has high levels of ammonia and potentially dangerous pathogens. This is why it’s recommended that it be aged or composted prior to its use as cow manure fertilizer.
  • Horse manure: It contributes to increasing soil fertility, regeneration and maintenance of high quality yields.  It helps fight the negative effects of salinity.  This manure improves the capacity of soil water retention.  Horse manure also improves soil water retention.
  • Poultry manure:  It’s the most common type of manure because of the common practice of poultry rearing.  It improves soil fertility and enhances the development of the roots system and the vigor of the plants that make them less susceptible to diseases and pest attacks.  This manure breaks down pretty fast in soil and produces a lot of heat.  That’s why I don’t recommend using it during directly warm seasons.  Compost it for 3-4 weeks.
  • Ovine (sheep/goat) manure:  The effects on soil fertility and the development of plants are not as fast as fish or poultry manure, but they preserve soil humidity.  They are mostly used as starting inputs since they break down slowly.
  • Hay, straw and weeds are also good organic fertilizers for the long term.  They have almost no available nutrients for a quick feed, but they contain lots of organics for the long term.

Growers Note: When 10% – 20% of worm castings were mixed with composted dairy, horse, chicken manure, or plant compost almost all bad odors were eliminated within 1-2 days.

Organic Fertilizer Values



Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.