Timing is Everything
When I first started growing pot in the early 1970's, the relationship between light timing and flowering was virtually unknown by the apprentice grower. Even though High Times began publication in 1974, the concept of 'bud cycle' was not apparent until Ed Rosenthal and Mel Frank published their first works in 1976. Prior to this, many of us simply grew big plants, either outdoors or under some form of artificial light, and just consumed whatever presented itself.
Those lucky enough to be able to grow outdoors and all the way into October were blessed with some pleasant surprises. The rest of us often learned the hard way what bunkweed was - a harsh and unpleasant tasting substance that produced little high and plenty of headache. Once Mel and Ed set us straight, our product's quality began to increase.
Cannabis needs to properly mature in order to be of value. The young plants will grow with vigor, like a weed. Young cannabis will flourish practically anywhere, under almost any conditions ? but it takes a special environment, and a specific set of circumstances, in order to properly mature. The key element is the timing of the light cycle. Like humans, plants have two worlds in which they exist: night and day. Day is when it is light and night is when it is dark. A thorough understanding of this simple fact is crucial to more fully understanding the nature of cannabis.
Sprouts, fresh clones and young plants live in what we refer to as the vegetative stage. This period has a long daytime and a short nighttime, like summer. It is during this vegetative stage that the plants send out much new growth. Large shade leaves form and act as sugar factories for the plant, turning sunlight into fiber for new growth. The plant needs to use as much food from the available light as it can, while it can.
This is why high nitrogen fertilizers are so beneficial during this period. The nitrogen, coupled with the extra light, acts as building blocks to the overall structure of the plant. As a general rule of thumb, in the indoor garden the average light cycle for the vegetative stage is 18 hours on and 6 hours off.
Bud cycle shift
At some point in the young plant's development it becomes time to begin the shift to what is called the flowering, or bud, cycle. It is during this period that the plants declare their sex and produce large floral clusters that become the buds. This stage has a shorter daytime and an increased nighttime, such as late summer and fall.
The large shade leaves begin to die and fall off as the plant shifts its energy from producing leaves and stem to producing floral clusters. Food from light and nitrogen decreases, and the demand for phosphorous and potassium increases to fuel the process. During the early flower stage the plant will go through what appears to be a growth spurt as the stems stretch to catch the light that, if outdoors, would be coming at a lower angle as the season progressed.
The floral clusters sprout from the areas where the leaves attach to the stems, called "nodes." The buds fill in the nodes and progress out. And, as we all know, it is strictly the female plants that develop into our high quality and most desired sensimilla. Indoors, the typical light cycle used in the bud stage is 12 hours on and 12 hours off.
Outdoors, the change in light cycle timing is gradual and slow, a little bit more every day. The transition between the plants' stages is therefore more drawn out and gradual. Indoors, the change in light cycle is usually instant: one day is 18 hours long and the next (and all those to follow) is 12 hours long. Under these indoor conditions the plant is forced to make the shift quickly, which is why the average length of the indoor flowering cycle is eight to nine weeks. This forced flowering has its advantages as the plants are made to finish up quickly, thus aiding production.
Oddly enough, plants do most of their fiber production at night, which may help to explain why such small vegetative plants are capable of producing so much bud in such a relatively short period of time. A well formed, six inch tall veggie plant (a plant in the vegetative stage) placed immediately into the bud cycle, is capable of producing an ounce or two of finished product in two short months, given adequate light, food and root space.
Nights of total darkness
An important thing to remember about the indoor bud cycle is that the dark period must be absolute and uninterrupted. The room must be thoroughly sealed to be completely dark when the lights are off. The only way to test this is to sit in the room in the dark, either during the day or with any lights outside the room on, to check for light leaks. It is advisable to allow your eyes to adjust to the darkness before declaring the room adequately sealed.
Once the bud cycle has begun it is important to never interrupt the dark period with any light, even for a short period of time. Doing so may interrupt the long, slow process of change that the plant had been working on up to that point. The plant may react by having to restart the process and seriously delay the scheduled maturation time.
I don't understand why it is that outdoor plants are not as sensitive to these nighttime interruptions. Perhaps it has to do with the unmatchable light intensity of the Sun. Stars, the moon and streetlights glowing through the low clouds over an urban area don't seem to hinder the outdoor plant all that much. For whatever reason, indoor plants tend to be ultra-sensitive to nighttime interruptions of light. So remember to make it dark and keep it dark.
Another aspect to consider is that Indica and Sativa varieties differ in their photo period expression, or photoreactive rate. The typical 18/6 and 12/12 light cycles are primarily beneficial to Indica varieties. Indica became the herb of choice early on in the industry due to its fast maturation and large production abilities under the HID lights. Indica is a variety from the 30th parallel and above, and this timing cycle is more akin to locations north of the 30th latitude (or south, in the southern hemisphere).
Sativa originates from equatorial regions, between 30 degrees north and 30 degrees south. Around the equator there is a much smaller difference between seasonal day lengths. The vegetative stage may be 13 hours of day and 11 hours of night, whereas the flowering cycle may be the opposite, 11 hours of day and 13 hours of night. There are pure Sativa strains that require three to four months to mature in the flowering cycle indoors. And although outdoor equatorial crops take such a long time to mature, it is often possible in the right areas to produce two to four crops per year, thanks to the tropical environments.
It will be interesting to see what specialized grow rooms, developed to provide a wider range of photo periods, would produce. More interesting will be what the wonderful and great outdoors will produce in all of her various environments. Light fortified greenhouses are capable of producing high quality herb just about anywhere on the planet. Once implemented, the global environment will surely reveal interesting and desirable variations, via careful selective breeding. In the meantime, further experimentation and research using different indoor light timing cycles would be very worthwhile.