Marijuana Grower's Handbook

by Ed Rosenthal

OVERRIPE BUD: The caps are falling off the trichomes and changing color. Photos: Rachael Smzajda, Courtesy of Harborside Health Center

  CRITICAL LIGHT PERIOD

  The 12/12 light-dark period formula has been accepted without question by growers all over the world. Probably one of the reasons for this was my discussion of the technique in some of my early books. The 12/12 regimen was selected because my co-author and I reasoned that no matter what critical period a variety might have, given 12 hours of darkness it will flower. However, most marijuana varieties need fewer than 12 hours of darkness to flower.

  If marijuana plants grown outdoors required a 12-hour dark period to flower, they would not be induced to start flowering until September 21st, the first day of autumn, when day and night are equal length. They would ripen 6-8 weeks later. Most modern varieties ripen between early September and late October. Budding was triggered six to eight weeks earlier.

  For instance, an eight-week variety that requires 55 days from forcing to maturity, which would normally ripen on October 1st, would start flowering August 1st. At that date in San Francisco, sunrise occurs at 5:14 am and sunset at 7:18 pm, a total of 14 hours 4 minutes. Dawn and dusk add another 15 minutes of red light. Plants use the absence of this spectrum to measure the dark period. The total lit period came to about 14 hours and 20 minutes, leaving nine hours and 40 minutes of darkness. The critical period for this plant was nine hours 40 minutes. If it were given just 10 hours of dark period daily indoors, rather than 12 hours, it would still flower. To initiate ripening, give plants an extra hour of darkness after the first 3 or 4 weeks of flowering.

  A forest of immature capitate trichomes. The caps that hold the THC and terpenes have not filled. Photo: Tom Flowers

  A single mature trichome. Notice the top has blown up like a balloon. Photo: Tom Flowers

  Electron micrograph of a single trichome in a forest. This gland is filled and ripe. Photo: Paul Mahlberg

  PHOTOPERIOD CHANGES BY MONTH & LATITUDE

  The further a region is from the equator, the greater the seasonal variations in light period.

  The latitude of your location affects ripening time. Take this into account when developing a growing strategy.

  Gardeners growing outdoors who discover the critical time needed to induce flowering can use this information to get more efficient use of their indoor garden. Currently, plants grown under a 12/12 cycle spend half their time in the dark. If the plants have a critical flowering time of, for instance, 10 hours of darkness daily, they can be provided 14 rather than 12 hours of light each day so that they receive almost 17% more energy with which to produce sugars used for more and faster growth.

  MANIPULATING LIGHT OUTDOORS

  Sometimes I think nature didn’t get it quite right on marijuana ripening, as far as we are concerned. If it were determined by human needs, the buds would be ready in late spring and ready to enjoy in early summer—the party season. If they ripened at the best time for the farmer, it would be in high summer when the weather was warm and the sun strong. Alas, nature has chosen the fall. The harvest can be good if the weather doesn’t attack first.

  ACTIVE SPECTRUM OF PHOTOSYNTHESIS

  The upper line shows sunlight reaching the top of the canopy. The lower line shows light reaching the under-story. Plants absorb or reflect most of the blue, green, yellow and red light. Some of it is used for photosynthesis. Far-red light (730 nm) is mostly transmitted or reflected, so there is a much higher ratio of far-red to red light under the canopy than in full sunlight.

  SUNLIGHT INTENSITY ON SUNNY AND CLOUDY DAYS IN EARLY SUMMER

  Notice the difference in the amount of light between sunny rather than cloudy days.

  With a bit of effort you can manipulate the outdoor light cycle to grow and flower the plants at your convenience. I think that the best and most convenient time to harvest is during the summer rather than the fall. Buds that ripen midsummer experience much more intense light and much more UV spectrum than fall ripened buds. The intense light gives the plant energy to grow a bigger bud. The UV light increases its potency.

  During the late summer through winter and mid-spring, the dark period is long enough to trigger plants to flower. Sativa dominant hybrids continue to grow even after they have been triggered to flower. Indicas grow just a little after they are triggered to flower.

  Another technique is to interrupt the dark cycle with light. The light doesn’t need to light the plant for long, just a few seconds. Think of it as a water spray. You want to get all the leaves “wet” with light, but once they have been sprayed they need no more light. This short interruption of the dark cycle is enough to reset the time count of uninterrupted darkness. By lighting the plants every few hours during the dark period, the plants continue to grow vegetatively, and not flower.

  FLOWERING CHART

  A. If the plants receive 18 hours of light, they do not flower. B. If the light cycle is interrupted by a dark period, the plants will not flower. C. When the plants receive 10-12 or more hours of uninterrupted darkness, they flower. D. When the dark period is interrupted, the plants won't flower.

  When the light interruption stops, the plants immediately start to flower. Plants can be started in August and planting can continue through the winter. To increase growth natural light can be enhanced using reflective material and electric lights. Spring starts on March 22nd and on that day light and dark share equal time. At the equinox, or shortly thereafter, the dark period may become too short to support flowering, and the plants will grow vegetatively.

  To get the best possible harvest, force spring plants to flower in June. If plants are forced June 1st, they will be ready mid- to late-July. If they are forced July 1st, they will ripen mid-August.

  EARLY HARVESTS & PHOTOPERIOD MANIPULATION

  In some areas, the light is intense enough and the temperature sufficiently warm to garden early in the year, sometimes beginning as early as February. Greenhouses increase the number of gardeners who can use this method. The only problem facing the gardener is providing the 14-15 hours of light the plant needs to grow strong vegetative growth.

  Plants started indoors can be placed outdoors in February and or early March, when they receive more than 12 hours of darkness and they will immediately start to flower. To keep the plants growing vegetatively, interrupt the dark cycle using periodic lighting at night. Since photoperiodism is a localized effect, the whole plant must be bathed in light for a short time to interrupt the flowering response. Both warm white fluorescents and HPS lamps can be used to prevent flowering because they are strong in red light but contain no far-red. The lights can be used a single time during the night cycle or, for best results, switched on every few hours. Once the plants reach the desired size, turn the lights off, and they will start to flower.

  If the temperature around the root ball becomes too cold, it can stunt plant growth. Although the light may have extended during the day, in colder areas it is difficult to plant outside due to frost risk. Thermoplanters from Black River Nursery keep the temperature of the root ball between 75-80° F (24-26° C), which eliminates root disease and fungus problems as well as cold root shock. It uses less water than a traditional planter because the heated planter evaporates the water back up to the plant. It comes with a plastic cover that converts it into a miniature heated greenhouse.

  The garden was in a warm area so the plants were placed outside early, in March. Since the nights were still long the plants would ordinarily have started to flower. By interrupting the dark period after five hours with bright lights the plants continued growing vegetatively. Several 24w warm white CFL fluorescents were placed in bowl reflectors and attached to a pole with clamps. Usually two people walked the pole over the plant rows. The plants didn’t need to be under the lights for long. A leisurely stroll once a night for 45 nights kept the plants growing vegetatively.

  This light, called a beam flicker, rotates the light back and forth to provide plants with enough light to interrup
t the dark cycle. It covers about 2,000 sq ft (190 sq m). It is much easier than a daily stroll and is automated using a timer.

  This technique of interrupting the night cycle may also be necessary for certain varieties in outdoor gardens in lower latitudes. For instance, most indicas and some indica-sativa hybrids flower very early in the season in the southern tier of the Northern Hemisphere because the light cycle never gets long enough to prevent it. Plants closer to a 50-50 indica-sativa mix withstand the long summer nights and continue growing a bit through part of the flowering cycle. These are good candidates for early harvests.

  LATE-SUMMER CROPS

  You can generate a late-summer crop by moving indoor plants outside late in the season. Most varieties start to flower when they are exposed to 10.5 to 11 hours of darkness daily. This occurs between late July and mid-August in most of the middle U.S.

  This home-built greenhouse was situated atop a building in Amsterdam. It helps grow beautiful buds to maturity in the short, cool, cloudy Dutch climate.

  Plants placed outdoors in July have a chance to grow a bit during the waning days of summer before longer autumn nights force them to flower. Plants placed outdoors in August, when the dark period has increased to 10.5 to 11 hours, will flower no matter what size they are.

  Sativas continue to grow a bit even as they transition to flowering. As flowering progresses, they put all of their energy into reproductive development, producing long colas filled with buds. They often require 90 days or more to ripen, so they can only be grown where the growing season extends into late October or early November.

  Sativa-indica hybrids continue to grow a bit although they are transitioning to flowering. They are the best varieties to grow in areas where plants can be harvested in mid to late October.

  Indica-sativa hybrids don’t grow much larger after they start flowering. They are likely to be shocked into flowering when they are placed outdoors after being grown under continuous light, so use 18 hours daily indoors. They ripen six to eight weeks after being triggered to flower.

  During the intense days of early August, indoor plants moved outside require conditioning in shade before being placed in bright light. An anti-transpirant can be used to help the plants withstand sunburn and adjust to UV light, which is mostly absent indoors under HPS lamps.

  WINTER CROPS

  This technique works best in conjunction with an indoor garden to supply plants. The idea behind this is that from late August through the beginning of February, plants placed outdoors are triggered to flower by the long nights. Plants placed outdoors start flowering and ripen within eight weeks.

  This technique can be used in subtropical and low-latitude mild-climate areas such as Florida, the Gulf Coast, Hawaii, Southern California, and the Mediterranean zone, all of which receive sunlight intense enough to support fast growth in winter.

  Light deprivation gives the gardener control over the light cycle outdoors and in greenhouses, allowing them to grow more crops, and crops out of season. The Light Deprivation Greenhouse by Forever Flowering uses a breathable fabric that rolls out with the flip of a switch. It allows the gardener to supplement light inside as well as block out light from the outside. They are environmentally friendly as well as convenient for overheard security.

  There are many advantages to growing winter crops:

  •They require less irrigation than summer crops.

  •Non-summer crops grow in a better temperature range. Temperatures lower than 85° F (29° C) support rapid growth and dense bud development. Temperatures above 90° F (32° C) stress the plant and decrease growth and result in looser buds.

  •Plants are less likely to be attacked by insects because fewer of them are around, and they are less active in lower temperatures.

  •The plants stay much smaller and are more controllable.

  •Cops and robbers are not looking for cannabis out of season.

  GREENHOUSES

  Greenhouses are ideal environments for extending the garden season. Even unheated greenhouses add three weeks of growing time to both the beginning and end of the season. You can gain another two weeks of growing time using passive heating techniques such as blackened water containers which absorb sunlight and radiate heat at night. Mechanically heated greenhouses can be used all winter.

  JUMP STARTING FLOWERING

  Long periods of uninterrupted darkness are nature’s trigger to marijuana to begin flowering. This is measured chemically by phytochrome, which is deactivated by red light. The inactive form is referred to as Pr. In the absence of red light, with a peak at 666 nm and effects from about 500-700 nm, Pr drifts into its active form Pfr, over a period of about two hours. This begins at dusk or when the lights are turned off. This transition period, during which Pfr has limited effectiveness, can be dramatically shortened.

  Pr is sensitive to far-red light with a peak at 730 nm and is affected in a range of about 700-750 nm. In its presence it changes almost immediately to the active form, Pfr. This effect is useful for shortening the two-hour time it takes plants to switch from the inactive to active form.

  Indoors, after the grow lamps are turned off, expose the plants to far-red (730 nm light) which turns the Pr to Pfr much faster and induces flowering within a shorter dark period. You can provde far-red lighting using LEDs or some fluorescents. Far-red light can also be used to restore the active form of the hormone if the dark is interrupted by light. This may ameliorate the consequences of darkness interruption.

  Outdoors, you have no control over dawn and dusk, but you can force flowering out of season by using far-red lighting to increase the time the plants are under Pfr’s flower-inducing influence by two hours. Plants receiving 15 hours of light and 9 hours of darkness react as if they were under a lighting regime of 11 hours of darkness because of the additional two hours of active hormone. Most plants initiate flowering under 11 hours of darkness, which is shortened to 9 after exposure to 730 nm far-red light. The plants should be exposed to far-red light each evening at the end of dusk. They need only a few seconds of the light each night.

  Growers in all latitudes can use this technique as well. In northern areas, the plants require supplemental illumination and heat in winter because the intensity of sunlight drops precipitously low beginning mid-November and continuing through mid-February. Even with the additional effort needed to meet the plant’s environmental and energy requirements, greenhouse gardening is far easier than growing indoors.

  Late ripening sativas can be forced to flower using light deprivation. By forcing them in late spring or early summer they will have enough time to ripen.

  These plants were harvested August 12 after seven weeks of flowering using light deprivation. After 12 hours of light the white/black shade curtains were placed over the plants. This took place between 6:00-7:00 PM. The curtains were removed shortly after dusk to prevent humidity build-up from condensation created by the plant transpiring. Make sure the framing is secure.

  Unheated greenhouses are often used to grow late-flowering sativas that need some protection from the changing climate. They can also be used to produce a harvest using late planting. By supplementing the weak sunlight of late autumn using metal halide lamps during the lit period, the yield can be increased substantially. The amount of light used during the daytime can be adjusted to take into account the sunlight’s intensity. Use 20 to 30 watts per sq ft (0.09 sq m) depending how dim the sunlight is.

  White/black plastic polyethylene is an excellent covering because it is opaque. Use the white side out, so the light is reflected and doesn’t heat the interior.

  Keeping the plants on a 12-hour schedule by lighting the plants at full-strength 60 watts per sq ft (0.09 sq m) at the beginning or end of the night also increases yield. For example, lights might be turned off from 11:00 am to 2:00 pm when the sun’s intensity peaks. A timer then turns on lights providing 30 watts per square foot for three hours as sunlight dims towards dusk. The second timer then kicks in when the 60 watt pe
r square foot (650 watts per sq m) lights are run for the few hours necessary to get to 12 total hours of light, then turned off. This can be configured with either two completely separate sets of lights —one that provides 30 per sq ft (25 watts per sq m) and a second set that adds an additional 30 watts (325 watts metric) to the late-afternoon lighting. Don’t use air-cooled reflectors if the temperature is below 80° F (26° C) in the greenhouse; the heat from the lamps and ballasts will help keep the greenhouse warm.

  High temperature can be a problem when forcing plants during the summer. Buds stretch and are looser and growth actually slows when the plant temperature rises above 85˚ F (29˚ C). There are several solutions:

  Water in hydroponic systems can be cooled using an aquarium water cooler or a hydroponic water chiller. Keep the root temperature in the high 60’s (19˚ C); the cool roots ameliorate the heat stress in the canopy.

  Misting fans and micro misting systems spray tiny water droplets that evaporate before they reach a surface. They use little water but can cool an area by 15˚ F (-9˚ C) or more. They are regulated using a thermostat, and turn on when the temperature nears 80˚ F (26˚ C) a the canopy.

  UVB LIGHT AND FLOWER FORCING

  Marijuana has evolved a very successful survival strategy. It domesticates easily and escapes domestication just as easily. Throughout almost its entire history of symbiotic relations with humans we accepted its natural life cycle without trying to alter it beyond developing varieties that matured a little sooner or later.