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

start ‘Haze’ on a 12/12 day/night schedule, but it still must go through the seedling and vegetative stages before spending three months or longer flowering. Plants grow more slowly in 12-hour days than when given 18 hours of light, and inducing flowering takes longer.

This ruderalis cross is blooming in the middle of summer. The photoperiod does not induce flowering in this plant.
    Indica -dominant varieties that originated in northern latitudes tend to flower sooner and respond more quickly to a 12-hour photoperiod. Many indica varieties will flower under a 14/10 or 13/11 day/nightphotoperiod. Again, the hours of light necessary to induce flowering in an indica -dominant plant is contingent upon the genetics in the strain. More hours of light during flowering can cause some strains to produce bigger plants with reduced flowering time, but some growers have reported looser, leafier buds as a result.
     
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    Give plants 36 hours of total darkness just before inducing flowering with the 12/12 photoperiod. This heavy dose of darkness sends plants an unmistakable signal to flower sooner. Growers using this technique report that plants normally show signs of flowering, such as pistil formation, within two weeks and develop pistils after a week of flowering.
    Growers have experimented with giving plants up to 48 hours of total darkness to jump-start flowering and have found that 36 hours-three contiguous 12-hour nights-is most effective.
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Half of this ‘Haze’ plant received light from a streetlamp, causing it to remain in the vegetative growth stage. The other half of the plant received total darkness at night and flowered!

Turn on a green light bulb to work in the indoor garden at night. Green light will not affect the photoperiod of flowering plants.
    Giving any cannabis variety less than 12 hours of uninterrupted darkness will not make it flower faster. Instead, the plant will take longer to mature, its buds will be smaller, and the overall harvest will be lessened.
    Genetically unstable strains could express hermaphroditic tendencies if the photoperiod bounces up and down several times. If you plan to give plants a photoperiod of 13/11 day/night, stick to it. Do not decide you want to change the photoperiod to 15/9. Such variation will stress plants and could produce hermaphrodites.
    Some growers experiment with gradually decreasing daylight hours while increasing hours of darkness. They do this to simulate the natural photoperiod outdoors. This practice prolongs flowering and does not increase yield.
    The photoperiod signals plants to start flowering; it can also signal them to remain in (or revert to) vegetative growth. Marijuana must have 12 hours of uninterrupted, total darkness to flower properly. Dim light during the dark period in the pre-flowering and flowering stages prevents marijuana from blooming. When the 12-hour dark period is interrupted by light, plants get confused. The light signals plants, “It’s daytime; start vegetative growth.” Given this signal of light, plants start vegetative growth, and flowering is retarded or stopped.
    Marijuana will not stop flowering if the lights are turned on for a few minutes once or twice during the flowering cycle. If a light is turned onfor a few minutes–long enough to disrupt the dark period–on two or three consecutive nights, plants will start to revert to vegetative growth. Less than one half of one foot-candle of light will prevent cannabis from flowering. That is a little more light than reflected by a full moon on a clear night. Well-bred indica -dominant plants will revert within three days. Sativa -dominant plants take four to five days to revert to vegetative growth. Once they start to re-vegetate, it takes four to six additional weeks to induce flowering!
    When light shines on a green object, green pigment in the object absorbs all spectrum colors but green, and the green light is reflected. This is why we see the color green.
    The smart way to visit a grow room during the dark period is to illuminate it with a green light. Marijuana does not respond to the green portion of the light spectrum, thus a green bulb is usable in the grow room at night with no ill effects.
    Some growers leave the HID on 24 hours a day. Marijuana can efficiently process 16 to 18 hours of light per day, after which it reaches a point of diminishing returns, and the electricity is wasted. (See Chapter Sixteen Breeding )
    I talked with Dutch and Canadian