When to flower
Santa Cruz, California
It depends on what size you want the ripened plant to be and the variety that you are growing. Once the light regimen is switched from vegetative (18 to 24 hours of light daily) to flowering (12 hours of darkness daily) the plant's growth changes to flowering.
After the light regimen is changed, varieties with mostly Indica characteristics grow another 25-50% before they stop vegetative growth. Most varieties offered by seed companies are hybrids with many Indica characteristics. They are suitable to grow as medium-sized plants, growing two to three feet tall with a canopy of about a square foot.
Many of these varieties can be used in sea of green set-ups. The plants are forced to flower at a height of 6-12 inches and are 15-24 inches tall at ripening, with a canopy of one-quarter to one-half square foot per plant.
Sativa plants tend to continue growing vegetatively for a while. Some pure Sativa varieties continue to grow to a certain size, usually three feet, even when forced to flower at 12 inches.
Many Sativas are also insensitive to 12/12 light regimens. The reason is that at the equator, which passes through Colombia, Congo, Borneo and near Panama, the light is near 12 hours all year around. They use other indicators of flowering time. These may include other factors, but the plant size and possibly its age are factors that determine flowering.
With some Sativas, flowering can extend for four months or more. The first flowers appear as the plant is still growing vegetatively and the plant puts more energy into reproduction as time passes.
Sativas from the 20th parallel have some light sensitivity but are still sensitive to their size regarding flowering. Land-races from Vietnam, Thailand, Jamaica and southern Mexico fit into this category.
Most commercial varieties of Sativa are actually hybrids with some Indica in their background. They are sensitive to light and generally ripen late in the season. Indoors, they are easiest to grow by giving them some room to spread out, at least two square feet of canopy per plant. They also need three to four feet of vertical space. They don't do well in sea of green set-ups.
Hybrid Sativas and Indicas can be forced to flower at any size. The quality of the buds is not time dependent, nor is it a factor of the size of the plant. Buds maturing on two clones from the same plant, one newly rooted and the other a large plant growing vegetatively for three months, will produce equal quality buds.
Ultimately, the decision is yours.
Figure out how big you want the plant to be when it's ripe. The smaller the plant is when it is forced to flower, the smaller the bud will be at ripening.
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