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time schedule for cannabis seeds

What is the Best Light Schedule for Maximum Yields?

Typically, the goal of growing weed is to have a large yield when it comes time to harvest. Whether you’re growing indoor or outdoor herb, light is one of the essential aspects of your grow. The light your plants get throughout their entire life cycle will have a tremendous impact on how much they weed they produce.

There are two major cycles of growing marijuana. These are the vegetative stage (when plants are growing) and the flowering stage (when plants produce flowers or buds).

Vegetative Stage

Being able to manipulate a plant’s light schedule makes it possible to achieve higher yields when it comes time to harvest. When plants are in the vegetative stage, the more light they receive the larger they will grow.

Even when growing outdoors, many growers will start their plants inside to ensure they can grow as large as possible. When in veg, plants should be kept under grow lights for a minimum of 18 hours (commonly known as 18/6). Some growers will keep plants under 24 hours of light during this time (known as 24/0) to allow their plants to grow as big as possible.

Marijuana plants don’t begin to flower until they begin to receive 12 hours of uninterrupted darkness. Until then, they’ll continue to stay in the vegetative stage. You can essentially keep your plants in veg forever as long as they’re receiving 13 hours or more of light each day.

Indoor Vegetative Light Period for Maximum Yields

Growing your plants indoors means you get to manipulate your environment as much as you want. When growing indoors, you can essentially keep your plants in the vegetative stage as long as you desire by keeping plants under light 18-24 hours each day.

It’s important to keep in mind however that it’s not just your light schedule during veg that will ensure a bigger yield come harvest. Some strains, such as Jack Herer and Northern Lights , simply produce more weed. And if you’re growing inside and don’t have high ceilings and a well-maintained grow room, your plants aren’t likely to get as big as you’d like them to be. Big plants with big yields need plenty of space to grow.

That being said, they also need plenty of light to reach their maximum potential. This is why some growers give their plants 24 hours of light each day. Stick with 18-24 hours of light during the vegetative stage and your plants will reach their maximum potential before it’s time to manipulate the light schedule to make them flower.

Outdoor Vegetative Light Period for Maximum Harvest

Many growers will start their grow indoors under lights before moving their plants outside to grow naturally under the sun. Starting seeds or cutting clones in March or April and keeping them under 18-24 hours of light until they’re moved outside in early May or June is common.

If you are growing outdoors , it’s vital you keep your plants inside until all danger of freezing temperatures is over. The last thing you want is for a late-spring snowstorm or sudden drop to freezing temperature to kill your plants. Once all danger of a cold snap has passed, plants will remain in veg outdoors from late spring until late summer.

Flowering Stage

Until plants have 12 hours of complete, uninterrupted darkness they will stay in the vegetative stage. They only begin to flower when they’re exposed to 12 hours or more of darkness each day.

Light Cycle for Indoor Flowering Period

When growing indoors, growers will typically put plants on a schedule of 12 hours of light and 12 hours of darkness (12/12) once plants have reached the desired size during the vegetative period. On average, growers veg indoor plants for 4-8 weeks under an 18/6 or 24/0 light period.

The key to growing indoor cannabis is mimicking what happens in nature. When grown outdoors, cannabis starts to produce flowers (buds) when the days begin to become shorter and they receive at least 12 hours of total darkness. All that’s needed to do this is to switch your light schedule from 18-24 hours of “sunlight” each day to 12 hours of light and 12 hours of darkness.

Light Cycle for Outdoor Flowering Period

If you’re growing outdoors, all you need to do is let nature do its thing. When grown outdoors, cannabis will naturally start flowering on their own. This typically happens after June 21 st , when days begin to become shorter.

This isn’t to say your plant will stop growing and only produce flower at this point. On average, plants will double in height after the begin the flowering stage both indoors and out. When growing outdoors, however, it’s extremely important plants aren’t exposed to light during the 12 hours they’re supposed to be in darkness. Even streetlights or floodlights can disrupt the flowering period. So, if you’ve got that neighbor who leaves on a floodlight all night that shines on your plants, you might want to see if they’d be willing to put it on a sensor.

Things to Keep in Mind for Light Schedules and Maximizing Your Yield

Whether you’re planning on growing indoors or outdoors, knowing the best light schedule to follow will help maximize your yield in the end. If you’re growing inside and height and space are not a big issue, letting your plants stay in the vegetative stage on an 18/6 or 24/0 light schedule for at least 60 days (8 weeks) is your best bet to grow the most bud.

If you’re growing outdoors, keep them inside on an 18/6 or 24/0 light schedule until all danger of frost and freezing temperatures are over and you can safely take them outside. Once they’re outside all you need to do is let nature do its thing as the sun rises and sets each day on its own.

Once the vegetative and flower stages are over (anywhere from 3-6 months), it’s time to reap what you’ve sown and harvest those big, beautiful buds.

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

Giving your weed less than 12 hours of light during flowering can both be an unnecessary complication and a way to boost a particular strain’s potential

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!