I’ve heard it asked many times; when should a cultivator ‘flip’ their cannabis plants into the flowering stage? The easy answer: any time! However, there are a lot of factors that could influence this decision. I won’t go into all the possible scenarios. Instead, let’s focus on your primary limiting factor – ceiling height.
Knowing how to force your cannabis to flower is the easy part. Simply use your timer to change to a 12hr/12hr (on/off) cycle for your light. Within 14 days you will see flowers form. Knowing when can take some initial calculations though because indoors we are limited in the height we can grow a plant. Artificial lights rarely penetrate more than 24 inches into a canopy either, so it doesn’t make sense to grow giant plants indoors. So how do we know?
The grower needs to figure out the tallest possible plant they can have. To do this, raise your lights as high as they’ll go and arrange the pots you wish to use under it. The light will hang a certain distance from the ceiling, measure and make a note of it. The manufacturer will suggest you keep the light a certain distance above your plants – make a note of this value. How tall is the top of the soil from the floor? Again, note the value. Now how tall are your ceilings? You got it, write that down too. Here’s what my notes look like:
| Ceiling height from floor | 8′ |
| Light/ceiling hanging distance | -1.5′ |
| Light/canopy separation | -.5′ |
| Top of soil from floor | -2′ |
| Maximum plant height | 4′ |
You can see from this example that, once you subtract the measured distances from my ceiling height, my maximum plant height is 4 feet. Ok, so how does this help?
The next step is understanding your cultivarA cultivated variety, often mistakenly called a 'strain.' More. As cannabis plants enter their flowering stage they will go through ~14 days of what’s known as ‘the stretch.’ During this time they grow upward explosively. For example; my orange kush stretched 28″ inches in the first 14 days of flower. Then, as suddenly as it began, the stretch ceased and they didn’t grow any more at all after that time. The overall height did increase slightly, but only by the amount of bud that it packed on. This plant started at 20″ tall so I know for future grows that this particular cultivarA cultivated variety, often mistakenly called a 'strain.' More will stretch to 2.4x its starting height – wow!
The good news is that most cultivars aren’t so stretchy, and some of it has to do with my setup. The rule of thumb to use is 2.5x multiplier if you want to be safe, or 2x if you want to be optimistic. Let’s use 2x for simplicity sake.
You’ve calculated that you can have a 44″ tall cannabis plant. This means that when the tallest plant is 22″ you need to force flowering. If you can have a 5.5′ plant then I’m jealous and you should force flowering when the plant is 2.25′ tall. Make sense? As you get to know your cultivarA cultivated variety, often mistakenly called a 'strain.' More you can dial in this number better as they will tend to stretch similarly in subsequent grows.
All that being said, even those watching closely may miss that perfect time to induce flowering. Perhaps your plant has grown 6″ too tall? Don’t despair, simply use some string and tie the plant down. Be creative!
Stay tuned as we will explore plant training in the near future.
Happy Harvests!
— The Lit Farmer —
