Simplistic setups work best, and this greenhouse—a representative setup—demonstrates just that. The medium here is ⅓ Fox Farms “Ocean Forest” soil, ⅓ vermiculite, and ⅓ perlite, mixed with water-retaining crystals. The containers are 2-gallon, and the plants in this picture, at three- to four feet tall in the flowering stage, need to be watered every other day. The nutrients used in this photo were General Hydroponics Flora Series as well as other amendments, as discussed later in the book.
In most environments plants cannot be placed outdoors in mid-Spring because temperatures are still too low for optimum growth. A greenhouse will keep the plants warm, day or night, even in cold or rainy conditions. Greenhouse-grown plants vigorously thrive. The clear plastic covering the greenhouse intensifies the sun and can elevate the temperature inside to roughly 85°F on a day when it is only 65°F outside—a temperature differential of 20°F.
When growing in a greenhouse you can produce three or even four crops per year, rather than one or two, as you can outdoors, uncovered. We place vegetated (approximately 24 inches tall) plants out into the greenhouse on April 20th and immediately induce flowering via light deprivation. (This deprivation is accomplished by using 6mm plastic that is black on one side and white on the other, with which we completely cover the greenhouse.) When the plants are fully mature and harvested, new, vegetated plants replace them immediately, and we repeat the cycle without losing a day of growth. And so on, repeating as we do in the symbiotic rotation process. In this way we get three crops by the first week of October.
When it starts to rain, we place industrial-use large dehumidifiers in the greenhouse to prevent powdery mildew and botrytis (gray bud mold); we also tightly close all of the doors in order to keep out the rain. On overcast or rainy days we augment with supplemental lighting. For example, in a 10 × 10-foot greenhouse we use two 600-watt metal halide and two 600-watt sodium halide lights, as one might indoors, which has the added benefit of raising the interior temperature to desirable levels on cold days. With the doors sealed, the greenhouse must still be allowed to ventilate to keep oxygen and CO2 levels in proper proportions.
Buds that are produced in a greenhouse are more like indoor buds than outdoors—they are denser, have more THC, etc.—because you have more control of the environment. There are lots of variables. For example, on warm days the doors at each end of the greenhouse are opened and both walls are rolled up and secured using bungee cords. Large oscillating fans are good to mount, to keep the air moving when the doors are closed and the sides rolled down. You must also install intake and exhaust fans.
Cover the greenhouse at night—you must have complete darkness inside to achieve optimum results. Try large sheets of 6mm Visqueen, white on one side and black on the other. The white side reflects heat off of the outside of the greenhouse and the black side absorbs heat on the inside. The cover is what allows you to induce flowering during months of extended sunlight.
These plants were two feet tall when placed into this 8×10 greenhouse in early August in Northern California. Then, due to fewer hours of available light, they immediately began flowering.
Photos: K
They reach full maturity in early/mid-October. This set-up was easy to produce and maintain.
The plants depicted above were two feet tall when placed outside into an 8×10 greenhouse in early August in Northern California (they began life indoors), whereupon, due to fewer hours of available light, they immediately began the flowering process. The plants reached full maturation in early/mid-October, and thus were in the greenhouse a total of eight-and-a-half weeks. This set-up was easy to produce and maintain. With added ventilation, heat, supplemental lighting, and a a good quality climate controller climate controller, this greenhouse produced the same quality of harvest throughout the winter months.
Greenhouse Grow Operations
Outdoor cannabis greenhouse with ceiling fans for air circulation.
A roving aisle allows easy access to every plant.
Photos: Better
Massive airflow is a must in a greenhouse.
Greenhouse extraction fan seen from exterior of garden.
Shade cloths are drawn to cover plants when the sun is at its most intense period of the day to eliminate unnecessary excessive leaf temperatures.
Elevated leaf temperatures cause unnecessary stress on the plants. Sun shades must be used in excessive light situations.
Photos: Better
Cola produced in a greenhouse garden.
Flowering cannabis in large cannabis greenhouse.
Flowering cannabis in large cannabis greenhouse.
Extraction fan to keep humidity and temperature levels appropriate in the greenhouse.
Photos: Better
The shade cloth visible in this photo can also be drawn in the evening to keep the plants warm at night and conserve energy on heating.
A worker tending to the plants in a greenhouse.
Small grow tents such as this, are perfect for hardening off clones.
Photos: K