We like to keep things simple.
And that means sticking to tried-and-true methods.
Weed that is growing outdoors enjoys long periods of daylight during vegging and around 12 hours of daylight and 12 hours of darkness during flowering.
That is why indoor growers provide 18 hours of daytime during vegging and then switch to 12 hours to induce flowering.
It works.
So obviously, we’re skeptical when presented with the completely different 6/2 light schedule. But we’re always willing to keep an open mind, so let’s take a closer look.
6/2 Light Schedule
A 6/2 light schedule means keeping your lights on for 6 hours at a time, then turning them off for 2 hours. You do this three times a day. This schedule is for vegging (or seedlings), but obviously not for flowering, which requires 12 hours of continuous darkness.
In terms of total amount of light, it is the same as the standard 18/6 vegging schedule (18 hours of light, followed by 6 hours of darkness). The light and darkness periods are simply broken up into 3 smaller chunks.
Breaking the periods of light and darkness up like that has several advantages, though most seem to be anecdotal only. It also has some potential disadvantages.
We’ll cover them next, but overall, we conclude that you’re better off just sticking to one of the regular time schedules, like 18/6, 20/4, or leaving grow lights on 24 hours.
Advantages Of A 6-2 Lighting Schedule
Below are the three most commonly cited benefits of a 6/2 lighting schedule. Only the last one is a proven benefit, and it is one that most growers won’t really need. The other two might help a bit, but probably won’t make much of a difference to your grow overall.
Gives Plants A Rest Period
The advantage most often cited for the 6-2 schedule concerns the amount of light plants can process per day. Once a plant has reached its daily limit, it can no longer absorb any light and continuing to give it light after that point is simply a waste of resources.
Providing 2 hours of darkness after 6 hours of continuous lighting gives the plant a chance to rest and process the light it received during those six hours. When the next 6 hours of light begin, the plant is ready to process more light. In this way, you maximize growth throughout the day.
This sounds like a compelling argument, and it very well may be, but we have not found any proof of this whatsoever. In fact, we have not seen any reports of growers having issues with 18 hours of light being too long. Many even provide light 24/7 during vegging and it does not seem to have any negative effects.
Prevents Light Stress
This is another unproven advantage. After 18 hours (or more) of continuous light exposure, marijuana plants can start to show signs of stress. These include droopy leaves or leaves that curl upward and they appear near the end of the light cycle.
If you only have the grow lights on for 6 hours at a time, these symptoms of stress do not appear. It strands to reason that shorter periods of continuous light are less stressful on the plants. What is not sure is whether a little stress actually has any negative effect on the plants. Every indication is that it does not.
Gives Your Grow Tent A Chance To Cool Down
If you are having trouble keeping your grow tent cool, a 6/2 lighting schedule might be beneficial. By breaking up the 18 hours of running your lights, and giving them 2 hour breaks every 6 hours, you also give your tent 2 hours to cool down.
This means you won’t need quite as much air conditioning, ventilation, etc. You also won’t have to run those systems for 18 hours straight, which put less stress on your fans and other equipment.
Disadvantages Of A 6-2 Schedule
The primary disadvantages of this lighting schedule are increased complexity and more stress on your plants when you switch from this 6/2 vegging schedule to the flowering schedule.
More Complicated
Having your lights come on and turn off 6 times a day is more complicated than doing it only twice a day. In fact, many timers are only able to turn them on and off once per day. They would not even be able to handle a 6/2 schedule.
This means you would have to get a timer that can turn the lights off and on multiple times throughout a single day. You would also have to set up everything correctly so that the lights come on and turn off when they should. And you’ll definitely need a timer—don’t even think of running this schedule while manually turning your lights on and off.
Naturally, you may want to program your cooling equipment to run concurrently with the lights. Or to increase in output when the lights are on and run at a lower setting when they are off.
Stress When Switching To Flowering Schedule
Switching from vegging to flowering is a bit unusual with a 6/2 schedule, because the length of time the lights are on continuously increases, instead of decreasing as it usually does.
If you use the standard 18/6 lighting schedule (or 20/4 or 24/0), the daylight period gets shorter when you switch to the 12/12 flowering schedule. But when you switch from a 6/2 schedule to bloom, the continuous daylight period actually gets longer, doubling from 6 hours to 12.
Like most of the benefits of this lighting schedule listed above, this drawback is also not proven. There are simply reports from growers who have seen their plants take much more time to adjust to the bloom schedule and to enter the flowering phase of growth.
Most likely, this will not cause a huge impact, but it is worth taking into account, if you are considering the 6/2 daytime breakdown.
One thing you could do to minimize any effects is to first change to a 10/2 cycle toward the end of vegging, before flipping all the way to the bloom schedule. This will help ease the transition and has the added benefit of giving your plants an additional 2 hours per day of daylight at a time when growth is really taking off.
Is It Worth Trying?
This is the big question. Is it worth trying the 6/2 vegging timetable? If you’ve read much of this site, you know we generally advocate keeping your marijuana grow simple. As simple as possible.
Thus, it should come as no surprise that we don’t recommend trying the 6/2 schedule. The possible benefits aren’t huge, most of the benefits are anecdotal only and have not been proven, and it’s going to be more work for you. Just stick with the 18/6 timetable that is easier to implement and has been proven to work well.
It is additionally worth remembering that plants in nature also live by the 18/6 (or a similar) schedule. They get their daylight in one continuous period, not broken up into 3. Plants have evolved to work with that.
All that said, using the 6/2 schedule is unlikely to have any major negative effects and it could possibly result in some faster growth. If you’re curious and don’t mind the extra work of getting it set up and ensuring it is running properly, there is no real harm in trying.
In fact, since there are a lot of questions online about the 6/2, but there are very few actual grower reports, you could document your results and help a lot of people.
What is really needed is a direct comparison growing the same plants under the same conditions in parallel, with only the light schedule being different. That could answer the question once and for all, which one works better.
6/2 Cannabis Lighting Schedule: Final Thoughts
Running your grow lights for 6 hours at a time, followed by 2 hours of darkness, is intriguing. No doubt about that.
But overall, we don’t feel it is worth actually trying, unless you have the spare time and capacity to do it. If you’re just trying to get a grow going and get a good yield, there’s already enough to worry about. Why complicate matters further for what will, at best, result in slightly faster veg growth?
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