,if you are growing not rushing,,you will go buy the strain of the plant,,, it's size will tell you when your plant is ready,,,, Biggest mistake I see is people tend to rush,,give it time let the plant become the strong mean plant it can be,,,,,,here is the math side,,works everytime,,,days can vary largly on the grow site strain and conditions,,the math won't change
Indica Strains
Most pure indica strains slow their vertical growth very quickly once switched to a 12/12 light cycle. It’s not uncommon for an indica strain to add only 25% to 50% to its total height after switching to a 12 hour light cycle. Most of this additional growth will take place in the first week or two of flowering. If an indica plant is switched to flowering when it is 12 inches tall it can be expected to finish flowering at about 18 inches, give or take. That math is pretty consistent, so a 2 foot tall indica will likely finish flowering around 3 feet tall.
Here is the equation for indica strains. The vegged plant height (V) multiplied by 1.5 equals the plant height at harvest (H) or 1.5V = H
Sativa Strains
Pure sativa strains are much more difficult to grow indoors and are becoming increasingly rare in general. I don’t recommend them for novice indoor growers for several reasons. What is important for this topic is that their growth after being switched to a 12/12 light cycle is unpredictable. Pure sativas often continue to produce significant vertical vegetative growth many weeks into the flowering cycle. Sativas often double in size while flowering, and in some cases, will finish at three times the height they were at when the light cycle was switched. A 12 inch plant switched to the 12/12 light cycle could end up as tall as 36 inches, sometimes even taller. This additional vertical growth can quickly become a problem in a normal grow room. I’ve seen growers flower sativas at 2 feet tall only to end up with 6 foot plants at harvest. Most grow rooms just can’t accommodate plants this tall, not to mention some other real
problems with tall marijuana plants.
Here is the equation for sativa strains. The vegged plant height (V) multiplied by 2.5 equals the plant height at harvest (H) or 2.5V = H.
Hybrid Strains
Hybrid cannabis strains are crossbreeds of various sativa and indica plants that have been bred selectively to promote specific characteristics. Some hybrids strains grow similar to sativas, other grow more like indicas. Most of the strains sold by seed and clone vendors are some form of hybrid. Find out as much about the strain as possible so you can guess how much vertical growth to expect after the flowering cycle beings. As a general rule, leave enough room for the plants to double in size. Once you are familiar with the strain you can let them grow a bit taller if there is room. Don’t forget, at a certain point, taller is not better.
Here is the equation for hybrid strains. The vegged plant height (V) multiplied by 2 equals the plant height at harvest (H) or 2V = H.
So if you go buy what you are growing there will be a perfect time to flower that type of plant or particular strain,,,Now Grow room size can dictate,,, how big you grow it,,,, but size not days will still let you know when to make the change so they can flower and still fit in there space,,,many people say it is this many days but if you are growing to reach the potential of the plant,,It will be size and overall health that tell you when,,,,This will not be what you do for a SOG style grow or some other grows ,,the Mathematical formula will always work,,,as some plants grow faster or may develope quicker just like people so time is what I give I want my plants to be potent and healthy,,,the size of the plant will mean the difference between grams,, OZ or Pnds
. I tend to cram 4-6 plants in a 4x4 area and to say training will help is great but there is typically no room to train, the whole thing is filled to the max. Yes some strains have stayed compact but most do not and lots of my hybrids triple in size over the flowering period.