Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible
Increased irrigation frequency is necessary to compensate for low water retention. Water- and air-holding ability and root penetration are a function of texture. The smaller the particles, the closer they pack together and the slower they drain. Larger particles drain faster and retain more air.
Irregular shaped substrates such as perlite and some expanded clays have more surface area and hold more water than round soilless mediums. Avoid crushed gravel with sharp edges that cut into roots if the plant falls or is jostled around. Round pea gravel; smooth, washed gravel; and lava rocks are excellent mediums to grow marijuana in an active recovery system. Thoroughly wash clay androck growing mediums to get out all the dust that will turn to sediment in your system.
Fibrous materials like vermiculite, peat moss, rockwool, and coconut coir retain large amounts of moisture within their cells. Such substrates are ideal for passive hydroponic systems that operate via capillary action.
Mineral growing mediums are inert and do not react with living organisms or chemicals to change the integrity of the nutrient solution. Coconut coir and peat mosses are also inert.
Non-inert growing mediums cause unforeseen problems. For example, gravel from a limestone quarry is full of calcium carbonate, and old concrete is full of lime. When mixed with water, calcium carbonate will raise the pH, and it is very difficult to make it go down. Growing mediums made from reconstituted concrete bleed out so much lime, they soon kill the garden.
Avoid substrates found within a few miles of the ocean or large bodies of salt water. Most likely, such mediums are packed with toxic salts. Rather than washing and leaching salts from the medium, it is easier and more economical to find another source of substrate.
Air is a great medium when it is filled with 100 percent humidity 24 hours a day.
Coconut fiber is an excellent hydroponic medium. See “Coconut Fiber” under soil amendments. Hit the site www.canna.com for detailed information about growing marijuana in coconut fiber.
Expanded clay, also called hydroclay, or hydrocorn, is made by many different manufacturers. The clay pellets are cooked at high temperatures in a kiln until they expand. Many little catacomb-like pockets form inside each pellet that holds air and nutrient solution. It is an excellent medium to mix with Peat-Lite and to grow mothers in large containers. I like the way it drains so well and still retains nutrient solution while holding lots of oxygen. Examples of expanded clay include commercially available Hydroton, Leca, Grorox, Geolite.
Some clay pellets will float.
Expanded clay can be reused again and again. Once used, pour expanded clay pellets into a container and soak in a sterilizing solution of ten milliliters hydrogen peroxide per four liters of water. Soak for 20-30 minutes. Remove expanded clay and place on a screen of hardware cloth. Wash and separate clay pellets from dead roots and dust. Let dry and reuse.
Coco is compressed into slabs and packaged in plastic. Add water to expand coco to full size.
Coconut fiber is also available in bags.
Expanded clay holds moisture and nutrients along with lots of oxygen.
Artificial foam slabs are used by some growers. To date they are still gaining popularity.
Pumice is a good growing medium. It can also be used as mulch or as an inert soil amendment
Peat moss mixed with perlite is one of the all-time favorite growing mediums. It is also an excellent soil amendment
Perlite is sand or volcanic glass expanded by heat. See Chapter Ten for more information.
Expanded mica is similar to expanded clay. For lots of exacting information on how and why this stuff works so well, check out www.hydroponics.com .
Foam is somewhat popular. It lasts a long time, lends itself to easy sterilization, and holds a lot of water and air.
Gravel is one of the original hydroponic mediums. Although heavy, gravel is inert, holds plenty of air, drains well, and is inexpensive. Still popular today, gravel is difficult to overwater. It holds moisture, nutrient, and oxygen on its outer surfaces. Use pea gravel or washed river gravel with round edges that do not cut roots when jostled about. Gravel should be 0.125-0.375-inches (3-10 mm) in diameter, with more than half of the medium about 0.25-inch (6 mm) across. Crushed rock can be packed with many salts. Pre-soak and adjust its pH before use. Gravel has low water retention and low
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