Howdy, and welcome to cannabis photoperiods, good peeps. I have mentioned pieces of this stuff in several lighting articles. But lately, I have been getting a lot of questions regarding photoperiods, so, I’m going to put it all in one place, here. Yay!
A photoperiod of 18/6 would be lights on for 18 hours, and lights off for 6 hours, per 24-hour period. A photoperiod of 24/0 would be lights always on. Using 24/0 is never a good plan in my opinion, and in my experience.
If you disregard photoperiods, and do things like veg your plants under a 24-hr. photoperiod, you will pay for it down the line. Producing sub-par cannabis is what you will achieve. Another thing I want to cover briefly, is when putting clones outside for the season, it is better to put them out a bit later than May 5th. Matching up the photoperiods will really make a difference. To calculate your outdoor photoperiod, use sunup to sundown, plus 1 hour.
When clones are put outside, and do that thing where they start to flower, then go back into vegetative growth, this really messes up your final product. Seriously messes it up when compared to clones that made a smooth transition into veg outdoors, from indoors. It taxes your plants hard; a lot of adapting must be done, this uses the clone’s resources on “wasted growth” basically, and confuses the hell out of them. Alrightythen, on with da show…
Cannabis Photoperiods for Sprouts
This is a very special time for plants. They are quickly adapting to their environment. Young seedling plants (sprouts) need to be popped under intense lighting. A minimum 200-watt light grow light, is what I would recommend. Now you can sprout your plants under an 18/6 or a 16/8 photoperiod, no worries. However, if you would like to be able to sex them (determine sex) easier, and at the time they have been above ground for 30 days, then read on…
Sprout your plants for their first 14 days above ground under a 12/12 photoperiod. Boom! That’s it. Then simply change their photoperiod to your normal vegging period. Once they are 30 days old, break out your magnifying glass, and sex your plants, easy peasy. This is normal for the plants, because in nature they sprout under shorter daylight hours as well. Cool, because less stress overall is good for plants, like it is for peeps. Happier plants make happier smoke, I say.
For landrace sativas especially, but any long flowering sativa dominant plants as well, you will want to keep the sprouts under the 12/12 photoperiod for a bit longer, like 17-18 days. 14 days is all good for 95% of the cannabis varieties out there.
Vegetative State Photoperiods
I like 18/6 as my vegging photoperiod. It is a tad “unnatural” but just one example of how you can leverage Mother Nature and push the rules a bit to get supernatural results. Using a 16/8 photoperiod is also all well and good. I have used both, many times, and I would recommend 18/6 here, hands down. Some varieties will try to constantly flower under 16/8 when their clones are over a year old.
It is fairly important to have your dark periods dark, even for your vegging plants. Again, less overall stress equals happier healthier plants. No light interruptions, and as dark as is possible are good rules for vegging.
Cannabis photoperiods for rooting clones should be no different than for vegging plants. I use 18/6 for rooting clones. Of course, I use a much more mellow light to root clones than to veg my cannabis plants. Many peeps like to root their clones on a 24-hr. photoperiod, and while this does root them faster, it leads to unhealthy, and unhappy, highly stressed plants down the line.
Holy hell, I must add here, to always use timers on your lights! Do not run your photoperiods manually. It only takes one screw up to do serious harm to your sinsemilla dreams. I myself have to open and close my tents daily. But my lights come on before I open things up, and they go off just after. I use alarms to warn me when it’s time to open and close.
Preflowering Cannabis Photoperiod
Some of you run growing rooms full term, veg to flower. Others, like me have a vegging room and a flowering room. In either case, this will matter. Rather than changing the photoperiod drastically from high energy veg to full on flowering, try transitioning. Like Mother Nature does it. This allows the plants to prepare to flower. Your flowering response will be faster, and better overall this way. Larger yields and improved quality, especially where terpenes and resin production are concerned. Here’s how we do…
It is fairly to very important that when you run your slightly decreased cannabis photoperiod for these two weeks, that you have the darkness periods fully pitch-black, like for flowering. Also, use the same lights/conditions as when flowering. Okay then, let’s continue…
For two weeks before starting your plants on their 12/12 cannabis photoperiod for flowering, you will want to take them to an intermediate photoperiod. If you veg on an 18/6 photoperiod, you simply change it to 16/8 for these two weeks. This signals your plants that they are losing daylight hours, while still having a lot of daylight hours to get stuff done. It tells them Fall is coming, in other words. In nature plants use the time of fading daylight hours to prepare for the big flower, that they know is coming. That’s what you are doing here.
Flowering State Photoperiods
I really shouldn’t have to say that the darkness time for your flowering plants must be pitch-black. There must be zero interruptions to that darkness with any kind of light. This is easy to precheck, just sit in your flowering room before it is full of flowering plants, and turn off the lights. Run all the nighttime equipment, and sit there for like 5 minutes. You’ll see any issues.
For flowering cannabis plants, my photoperiod is 12/12—except with landrace sativas, it’s 11.5/12.5. Pretty straight forward there. Now, as a protection against power failures, you can have some small LED lanterns at the ready. You don’t ever want your plants going DARK during their lights on time, for more than a few minutes. You only need to add some light, just to fool them that the sun is still up.
If you are not home, you can run a setup so when the power fails special lights come on for your plants to ride them through, like lower wattage LEDs or whatever. BUT—you must make sure these lights do not come on if the power fails during nighttime hours. This will cause serious problems! I used to run this way and just unplugged the power-out lights every night and plugged them back in every morning. Worth the hassle if you are on a sketchy electrical grid and not home a lot.
Running healthy cannabis photoperiods is a great way to up your game if you don’t do it already. It’s another good tweak to your overall skills when growing cannabis. These all add up homie. Together they become more than the sum of their parts. Here’s another cool article by yours truly: TLO Micropond Growing Style 2021 – Skunk Magazine. So, check that out if ya wanna. Visit KOS for some stellar cannabis seeds, and grab a copy of my TLO Book while you’re at it.
I hope you all have a great week. My county is still all locked down in extreme risk, ugh. Haven’t even been able to get out on the Mean Green bicycle due to weather. Working a ton, especially on the upcoming book. Make sure to have a copy of my 2nd edition if you plan to get the new book. It will help a lot regarding referencing details. Even working so much has bad side effects on an old Magoo like me, and so I am always throwing out my back and cool stuff like that—LoL 😂 adapting must be done, and my hunny’s help must be summoned! I am super grateful to have a hunny to help!
See ya all back here at SKUNK next Tuesday for a new article. Hope you enjoyed this read. L8r G8rs…
I'm The Rev, and I have been with SKUNK for about a decade now. I hail from Southern California, spent mucho time in Northern California, and now reside in Southern Oregon; always coastal. I am an all natural style cannabis grower and I have written a couple books on the subject - check out True Living Organics 2nd Edition on Amazon - I have been growing for over 45 years, and I have been breeding cannabis for over 30 years. Check out kingdomorganicseeds.com to see some exotic selections. Growing connoisseur cannabis is what I teach mostly, growing it in living soil without using liquid organic nutrients to feed the plant. I am also a highly skilled synthetics grower, hydroponics, aeroponics, DWC/SWC/NFT, Ebb and Flow, and soilless, but I cringe when smoking synthetic grown herbs, so for the last 15 years or so I preach the artisan style of all natural growing, specializing in container growing. Cheers and welcome aboard.