Flip your plants from vegetative to flower stage with 12 hr light cycle after 3 to 5 weeks in veg. Switch from veg to flower when the plants are half the total height or width of the grow space to allow room for them to mature. Flipping between 3 to 5 weeks is best for flower development and THC concentration.
Lots of small plants or fewer large plants?
Think of your plant canopy like a solar panel. You want the leaves to fill the grow space under the light so the maximum amount of the light is absorbed. If you grow one plant in a large grow area it will take a long vegging time to fill the space. If you grow four plants in the same space it will take about 1/4 of the veg time for the plants to fill the space. However more plants means more pots, drip feeders etc.
Plants will double in area after switching light cycle
Whatever number of plants you are growing you should switch to flower once the plant canopy area is over half the grow area.
Plants will double in height due to stretching when you switch to flower
Another factor to consider is how tall your plants will get in your grow space. As a general rule of thumb plants will double in height after you switch them to flower. This depends on genetics, Sativa varieties will stretch more than Indica plants.
Flipping early to veg for larger flowers
A recent study* has analysed 26 studies of growing results. The study shows (figure A) that flipping to flower in the first 3 or 4 weeks results in plants with larger flowers. The longer you wait the bigger the plants will be but the proportion of flowers will reduce slightly.
Flip at about 6 weeks for maximum THC
The same study compared the % THC at harvest time to the number of days the plants were flipped to the flowering cycle. The results (Figure B) show the optimum time to switch to the 12/12 light cycle for flowering is about 40 days or 6 weeks. However is seems flipping to flower anytime from 3 to 8 weeks will deliver a potent harvest with high THC content.
*'Optimizing Photoperiod Switch to Maximize Floral Biomass and
Cannabinoid Yield in Cannabis sativa L.: A Meta-Analytic Quantile Regression Approach'
Michelle Dang, Nishara Muthu Arachchige and LEslie G. Cambell
Department of Chemistry and Biology, Ryerson University, Toronto
