Short Guide to Organic Fertilizers for Medicinal Marijuana

We??re slowly working on a more complete medical marijuana growing guide that will include an entire series of essays and entries similar to our previous Guano Guide / Manure Manual as well as our Molasses Manual. As that work progresses, we??ll be including bits and pieces of our research,

Table 1. A Selection of Organic Fertilizers for Use in Growing Mediaa
Fertilizer Material

Estimated N P K Rate of Nutrient Release Salt & pH Effects


Alfalfa Meal 2.5 0.5 2.0 Slow

Blood Meal 12.5 1.5 0.6 Medium-Fast

Bone Meal 4.0 21.0 0.2 Slow

Cottonseed Meal 7.0 2.5 1.5 Slow-Medium Tends to acidify

Crab Meal 10.0 0.3 0.1 Slow

Feather Meal 15.0 0.0 0.0 Slow

Fish Meal 10.0 5.0 0.0 Medium

Granite Meal 0.0 0.0 4.5 Very Slow

Greensand 0.0 1.5 5.0 Very Slow

Bat Guano 5.5 8.6 1.5 Medium

Seabird Guano 12.3 11.0 2.5 Medium

Kelp Meal 1.0 0.5 8.0 Slow Possibly high-salt

Dried Manure Depends on Source Medium Possibly high-salt

Colloidal Phosphate 0.0 16.0 0.0 Slow-Medium

Rock Phosphate 0.0 18.0 0.0 Very Slow-Slowc

Soybean Meal 6.5 1.5 2.4 Slow-Medium

Wood Ash 0.0 1.5 5.0 Fast Very alkaline, salts

Worm Castings 1.5 2.5 1.3 Medium


(a) Information in the table has been adapted primarily from Penhallegon, Ross. 1992. Organic fertilizer NPK values compiled. In Good Tilth. January. p. 6.; and Rodale Staff. 1973. Organic Fertilizers: Which Ones and How To Use Them. Rodale Press, Emmaus, PA. p. 50.

(b) Cottonseed meal from many sources may be too contaminated by routine pesticide use to be permitted in certified production. Growers should consult their certifiers before using.

(c) The availability of phosphorus in different forms of rock phosphate depends on the pH of the mix, biological activity, fineness of grind, and the chemical composition of the source rock. Precise performance is not easy to predict.

The preceding table was originally sourced from the website for ATTRA - National Sustainable Agriculture Information Service.

The numbers presented in this table should only be considered a rough guide to some manure based fertilizers such as bird and bat guano, who??s nutrient value often depends on a variety of factors.







heres another good 3lb content that has information on the time release of some common organic ferts

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