By Professor Lee
Indoor growers can speed up the flowering cycle of traditional and feminized strains of cannabis by simply changing the amount of light the plants are exposed to between regular dark periods. A lot of growers are familiar with short light cycle methods like 11 on 13 off, 10 on 14 off, 9 on 15 off and 8 on 16 off. Each hour that the light cycle is reduced, up to 4 hours, directly translates to a reduction in the length of the floral cycle. Basically the plants think that winter is bearing down on them and they need to finish up as quickly as possible. The disadvantage is a proportionate reduction in harvested bud weight.
The alternative long light cycle technique shortens the flowering cycle of plants without sacrificing bud weight. The long light cycle I always recommend is the 24 on 12 off cycle. This method can reduce the flowering cycle of cannabis plants by up to a week for every month of growth. So a plant whose floral cycle normally takes 60 days can finish up to two weeks early, and/or a plant that normally takes 90 days can finish up to three weeks early. The equipment needed to introduce a long light cycle is a programmable timer that allows the grower to program the on/off cycles over the course of an entire week. A simple search for "7 day timers" on the Internet will produce lots of results.
Here's why this method works so well. Out of the 168 hours in a week a traditional 12 on 12 off light cycle gives the plants a total of 84 hours of light to grow. An extended 24 on 12 off cycle provides the plants with 120 hours of light per week. Over the course of a 30 day month the plants get exposed to 516 hours of light instead of only 360 hours. The 156 hour advantage translates into 6.5 days worth of extra growing time per month.
Funnily enough, a 30 hour on 12 hour off cycle also provides the plants with 120 hours of light a week. The long light cycle technique has its limits and 24 on 12 off is about it. Using a crazy cycle like 36 hours on 12 off or 48 hours on 12 hours off looks good on paper, but most plants simply can’t finish much sooner than the more accommodating 24 hour on 12 off cycle. Using any other long light cycle has the tendency to leave the grower with a mild form of schizophrenia as they try to remember if the lights will be off and on during any given day.
A seven day week is an odd number which means that a 24 on 12 hours off cycle won't perfectly repeat itself. For example if you start your timer on Sunday and run it for 24 hours the following will happen. Monday will be dark from midnight until noon then light until midnight. Tuesday will be light from midnight until noon then dark from noon until midnight. Wednesday will be light all day. Thursday will be dark from midnight until noon then light from noon until midnight, Friday will be light from midnight until noon then dark from noon until midnight. Saturday will of course be light all day, and here's the rub, when the timer then turns to Sunday another 24 hours of light begins. This gives the grower a solid 48 hour block of light to work with. I used to work weekends, but had Mondays and Tuesdays off so I treated these days as my weekend and made the most of it.
Over the course of the week the plants received 4 periods of 12 hour darkness and 5 periods of 24 hour light. I've based all my numbers off of this schedule. If a grower wants to avoid the 48 hour block they will have to reprogram the timer every week to maintain a perfect “24 on 12 off, 24 on 12 off, 24 on 12 off” type of schedule. I don't recommend this. For all the extra work one does, a grower actually loses 36 hours of light over the course of the month. That’s a loss of 1.5 days worth of growing time. Likewise, if a grower starts their 24 hour on 12 off cycle with 12 hours of darkness then the plants will be exposed to 5 periods of 12 hour darkness and 4 periods of 24 hour light and one odd 12 hour period of light left over at the end of the week. This alternative schedule also means that over the course of the month the plants are exposed to only 96 extra hours of light or 4 days worth of time. That’s a loss of 2.5 days every month.
When starting a long light cycle it is advisable to force flower the plants with the traditional 12 on 12 off system. This will trigger pre-flowering much quicker than starting with the long light cycle. Once the initial pre-flowering phase passes, meaning that true flowers have started to appear, switch to the extended long light cycle to
finish flowering the plants. This can sometimes get a little awkward when a grower has plants of different ages in the same floral garden but it can be done. Most growers using long light cycles prefer to have all of the floral plants to be the same age to simplify things.
In conclusion, it's possible to speed up the flowering cycle of traditional and feminized cannabis strains simply by investing in a new timer and rethinking one’s schedule. These reductions in general harvest times are all best case scenarios and don't deal with all the variables one encounters when growing, but it will speed things up.
And who doesn't want to harvest buds faster?
Author of Marijuana 101: Professor Lee's Introduction to Growing Grade A Bud
and Q&A Guru for Weed World Magazine.
This article first appeared in issue 104 of Weed World Magazine