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

purchase a light meter ($30-50). It will be very useful in setting the light level in your greenhouse for maximum efficiency.
    Carbon Dioxide (CO 2 ) is another important aspect of the greenhouse environment that will be only touched upon in this section. Closed greenhouses often have too little CO 2 during the day for plants to be able to use light effectively. Enhancing the levels of CO 2 will accelerate plant growth; methods for doing so range from expensive CO 2 equipment with infrared sensors to block dry ice kept in a pressure bottle until needed. More detailed information on CO 2 can be found in Chapter Thirteen, “Air.”

Over the last decade, the soil in this Spanish glasshouse has been regularly amended with organic matter. The growers put lightweight hydroclay on soil surface as mulch that does not decompose.

This beautiful greenhouse was grown by the legendary Shantibaba in Switzerland. After an extended stint in Swiss prison, he is free!

Greenhouse buds in all directions!
    Security is always a concern when growing cannabis. There are several ways to camouflage the greenhouse such as growing other plants with the cannabis. Paint the walls with sun-blocking paint so light still enters but prying eyes do not. Go to the discount store and purchase artificial flowers. Put the artificial flowers on and around the cannabis plants so it looks like they are growing from the cannabis. Remember to pay attention to other plants that could be blooming during this time and follow suit.
    Planting in the earth floor of the greenhouse allows you to use organic methods. The plants cannot be moved easily, but they grow bigger and require less maintenance than container-grown plants. Without containers, plants also retain a lower profile. Growing in Mother Earth is always better than planting in pots! Most all the principles that apply to outdoor growing apply to growing in a greenhouse, too. Check out Chapter Seven, “Outdoors” and Chapter Ten, “Soil & Containers” for more information.

Seeded female from Next Generation seeds in British Colombia, Canada is one of the new and upcoming companies.
    Greenhouses can be darkened to induce flowering during mid summer. This practice will allow you to harvest up to three crops a year! Cannabis plants flower when nights are long (12 hours) and days are short (12 hours). Darken the greenhouse so that plants receive 12 hours of uninterrupted darkness every day to induce flowering. When the greenhouse is darkened daily so that plants receive 12 hours of darkness, a crop of clones planted May 1st can be harvested by the middle of July.
    Automatic darkening machinery is available for large commercial greenhouses. Smaller greenhouses are normally covered with black plastic to “black out” the interior for 12 hours.
    When combined with natural sunlight, artificial light is optimally used during non-daylight hours. Greenhouse growers turn the HID lights on when sunlight diminishes (30 minutes before sunset) and off when sunlight strengthens (30 minutes after sunrise). Turn on the HID when the daylight intensity is less than two times the intensity of the HID. Measure this point with a light meter. Turn off the HID when the daylight intensity is greater than two times the intensity of the HID. A simple photocell that measures light intensity can be used to turn the lights on and off automatically.
    Supplementary lighting has greatest effect when applied to the youngest plants. It is least expensive to light plants when they are small.
    Many different types of coverings are available for greenhouses and cold frames. The best greenhouse films are UV (ultraviolet) resistant and still transmit plenty of light. Lexan is rigid and full of thermo-storing channels. It is one of the best greenhouse plastics available. Lexan lasts for years and transmits almost as much light as glass while retaining greenhouse heat. The only problem with Lexan is that it is clear! Some growers disguise greenhouse cannabis by wiring ornamental plastic flowers to the branches visible to passers by, which is advisable where neighbors are not curious and laws lax.

This Swiss grower moves the covering over plants in the afternoon and opens it after dark. The coverings slide over smooth wires strung between wooden posts.
    Regulating heat in a greenhouse is much more difficult than in an enclosed grow room. Greenhouses heat up quickly on sunny days and cool equally fast when the sun ducks behind a cloud or