Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible

potash and several trace elements. Releasing nutrients slowly over several years, granite dust is an inexpensive source of potash and does not affect soil pH. Not recommended indoors because it is too slow acting.
    Greensand (glaucomite) is an iron-potassium silicate that gives the minerals in which it occurs a green tint. It is mined from ancient New Jersey-seabed deposits of shells and organic material rich in iron, phosphorus, potash (5 to 7 percent), and numerous micronutrients. Some organic gardeners do not use Greensand because it is such a limited resource. Greensand slowly releases its treasures in about four years. This is too slow acting for indoor gardens.
    Guano (bat) consists of the droppings and remains of bats. It is rich in soluble nitrogen, phosphorus, and trace elements. The limited supply of this fertilizer-known as the soluble organic super bloom-makes it somewhat expensive. Mined in sheltered caves, guano dries with minimal decomposition. Bat guano can be thousands of years old. Newer deposits contain high levels of nitrogen and can burn foliage if applied too heavily. Older deposits are high in phosphorus and make an excellent flowering fertilizer. Bat guano is usually powdery and is used any time of year as top-dressing or diluted in a tea. Do not breathe the dust when handling it, because it can cause nausea and irritation.
    Guano (sea bird) is high in nitrogen and other nutrients. The Humboldt Current, along the coast of Peru and northern Chile, keeps the rain from falling, and decomposition of the guano is minimal. South American guano is the world’s best guano. The guano is scraped off rocks of arid sea islands. Guano is also collected from many coastlines around the world, so its nutrient content varies.
    Gypsum (hydrated calcium sulfate) is used to lower the soil pH, and it improves drainage and aeration. It is also used to hold or slow the rapid decomposition of nitrogen. This is seldom used indoors.
    Hoof and horn meal is an excellent source of slow-release nitrogen. Fine-ground horn meal makes nitrogen available quicker and has few problems with fly maggots. Soil bacteria must break it down before it is available to the roots. Apply it two to three weeks before planting. It remains in the soil for six months or longer. Hoof and horn meal contains from 6 to 15 percent nitrogen and about 2 percent phosphoric acid. We advise avoiding use of any dried blood or bone meal that could carry Mad Cow Disease.

    Bat guano has transformed into the organic super bloom fertilizer.
    Horse manure is readily available from horse stables and racetracks. Use horse manure that has straw or peat for bedding, since wood shavings could be a source of plant disease. Compost horse manure for two months or longer before adding it to the garden. The composting process kills weed seeds, and it will make better use of the nutrients. Straw bedding often uses up much of the available nitrogen. Nutrient content of horse manure is N – 0.6%, P – 0.6%, K – 0.4%, and a full range of trace elements.
    Kelp is the Cedilla of trace minerals. Kelp should be deep-green, fresh, and smell like the ocean. Seaweed contains 60 to 70 trace minerals that are already chelated (existing in a form that’s water soluble and mobile in the soil). Check the label to ensure all elements are not cooked out. See Seaweed on this page.
    Oyster shells are ground and normally used as a calcium source for poultry. They contain up to 55 percent calcium and traces of many other nutrients that release slowly. Not practical to use indoors because they breakdown too slowly.
    Paper ash contains about 5 percent phosphorus and over 2 percent potash. It is an excellent water-soluble fertilizer, but do not apply in large doses, because the pH is quite high. Paper ash is also full of toxic inks.
    Pigeon manure has a very high concentration of nitrogen but is difficult to find. It can be used in the same fashion as chicken manure.
    Rabbit manure is also excellent fertilizer but can be difficult to find in large quantities. Use rabbit manure as you would chicken or pigeon manure. According to John McPartland, rabbit poop is the best. Bunnies rule!
    Potash rock supplies up to 8 percent potassium and may contain many trace elements. It releases too slowly to be practical indoors.
    Rock phosphate (hard) is a calcium or lime-based phosphate rock that is finely ground to the consistency of talcum powder. The rock powder contains over 30 percent phosphate