Can having light on 24/7 hurt the plants?

I’ve read that 24 hours doesn’t hurt and can only help, but now I’ve also been told that plants need some darkness too.

Any advice appreciated.

Plants do better with a rest period… Some of us put the plants to sleep using far red lights… On 5 minutes before lights out… Off 10 minutes after lights out.

I forgot what it is called… But if you look in nature around sunset…you may see it.

I had a pic but cannot find it now.

Veg is best at 18/6
Flower at either 12/12 w/o red lights… Or 13/11 with red lights.

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Many plants do; however; cannabis is a C3 plant that does not require a dark period to complete all necessary biological processes. It does not require a dark period.


I grow photo and do the typical 18/6 during veg.

Midwest is right though on the C3 plants and not needing a dark period, but I would add during veg and only with photos. We know with photos, we have to drop the light to 12/12 to get bud. To summarize in rhyme, With photos during veg let her rip until flower then drop to 12/12 for the flip. I am not sure of the control but one of the articles I read stated you should see about 33% more growth during veg leaving the lights on 24/7 instead of 18/6 with all other variables being the same.

Be sure to set your DLI to 24 hours if you use a DLI app.


Great point. Autos don’t care, but photos can present a problem with extended light hours when attempting to flower photos.


I’ve vegged both ways, and never really noticed a significant difference, so i do 18/6, and save a little electricity.


I guess I’m most interested in learning if 24 hour light is harmful ( to the plant , not to your wallet) Sounds like you’re saying no, but others sewm to be saying yes.

It makes no difference to the plant, but once the plant’s DLI requirements are met, no additional light is helpful.


Some things you make the best decision based on what you/we know and keep on growing. Like I mentioned I do use 18/6 through veg but I know I do not “HAVE” to. Another article I read stated Cannabis photosynthesizes during the day and metabolizes the work done during the day at night. So that is why I offer a night cycle.

Well if it doesn’t help then of course it makes sense not to spend the extra $.

But ar least I don’t have to worry about hurting the plant if I accidentally let it sit more thsn 18 hours under light.



compromise? 20/4, I would hit all three, for experimenting…

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:point_up:t3: this right here. Outside of flowering photoperiod plants, which was already mentioned.


I’m running 20/4 on these autos and did 18/6 last autos. Going to see if a couple extra hours do anything to yield or bud size/structure. Loving these experiments were able to do


I’ve done more reading and have found sources saying the cannabis plants can get a “sunburn “ from too much light, although this seems more directed at the distance the light is from the plant, not the duration of exposure to light.


You got that right. We learn and share. Thanks.

Same to

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