11/13 Flowering Light Cycle: Can it Improve Your Grow?

14 December 2020

Table of Contents

When growing photoperiod marijuana, it’s a standard practice to give it 18/6 in veg and 12/12 in flower. However, there are growers who use a shorter photoperiod and swear by it. Let’s review the existing studies and anecdotal evidence and see if 11/13 flowering light cycle and similar light schedules really work.

What Does Science Say on Flowering Under 13/11?

It’s notoriously difficult to find any peer-reviewed scientific publications on the subject of cannabis cultivation. The question of using 11/13 for flowering is no exception. There’s one major paper that studied the effects of light (intensity, spectrum etc.) on cannabis production. It only briefly states that shorter photoperiod potentially leads to smaller yields*. Well, it’s expected, and this is the same thing as growers on forums say.

Another study actually focused not on medical marijuana, but on hemp grown for fiber. It also noted that shorter photoperiod causes earlier flowering**. The researchers observed little difference in flowering times if days lasted 13 h 40 min or less. However, if light hours were at 14 h 40 min or more, this significantly delayed the beginning of flowering (and the harvest time).

Well, hardly any real-life grower has ever experimented with a 14/10 cycle, so this doesn’t give us much insight. It’s interesting that both 12/12 and 13/11 fall into the “13 h 40 min or less” category, and the scientists didn’t find the difference statistically significant.

And in case you’re wondering what’s the maximum length of day at which most cannabis plants start to flower indoors, it’s 13.2 hours (and 10.8 h of dark)***. So not only the ‘11 on 13 off flowering’ light schedule, but also the opposite (13 on 11 off) can be used for flowering. At least, for indicas and indica-dominant strains.

And that’s it in terms of reliable scientific data. Let’s hope we get more in the future.

What’s the Consensus in the Growing Community?

It’s very difficult to obtain objective results of whether the 13/11 flowering cycle works for you or not. To get hard evidence, you’ll have to run a side-by-side experiment. Nobody has bothered to do this so far. So we don’t know for sure. Still, there are several points that all 11/13 growers agree upon:

A slightly shorter flowering time. Comes handy if you’re in a hurry, or want to save a day or two worth of electricity.
A slightly lower yield. Here you have a classical tradeoff between speed and reward. You can try to offset this with more powerful lights though.
Saving electricity. Even if the 13 11 light cycle doesn’t make the flowering shorter, you’ll save 1 hour a day worth of energy.

More Controversial Findings on 11/13 Flowering Light Cycle

Perhaps, the list above didn’t inspire you to try less than 12 hours of light during flowering? Well, here are a few extra points that’ll probably change your mind.

At least two celebrity breeders—the legendary DJ Short of the Blueberry fame and Swerve from Cali Connection—recommend to shorten the day during flowering. DJ Short believes that this method is great for breeding. It’s because it increases the expression of sativa genes in a hybrid. This affects the plant structure and the shape and the texture of buds (e.g. foxtailing). More importantly, it also influences the high. Presumably, the standard 12/12 cycle makes the effect more couch-locky. And if you want more of the cerebral sativa energy, you better make light hours shorter and darkness longer. The effect of 11/13 grown buds also tends to be a creeper, according to anecdotal reports.

Some people say that they’ve noticed less stretch on 11/13 during flowering. Which means that you should give your plants a longer veg than normal if you want the same final height.

There’s much controversy about whether the 13/11 flowering time produces more trichomes or less. Some think less light equals less THC. Others say THC gets degraded by light, so more hours of darkness means more potency. Anyway, if you want more resinous buds, the 11/13 method doesn’t seem like a good idea. You may want to try the extended dark period before harvest instead.

Don’t be Afraid to Experiment with 11/13!

For people who love to tweak their growing conditions, changing the photoperiod during flowering presents a lot of opportunities. Just keep in mind that, with days lasting more than 14h 40min, no flowering usually happens. But anything less than that is acceptable and gives you a lot of room for trial and error.

Try and experiment with incremental changes of 15 minutes over several consecutive grows until you hit a sweet spot. For example, you may find that 10h 30 min on / 13 h 30 min off works best for a particular strain. However, you’ll have to find it for yourself—there’s no one-size-fits-all solution. Maybe the tried and true 12/12 schedule would be perfect for you after all? Who knows!

Please tell us what you think in the comments!

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