Light cycle for AutoFlowers

Hello All,

I have a totally new bee question. I am growing my very first Auto Flower. My question is about light. Or to be more specific, Length of lights on and off. I am running a 1500 W LED in a 4’ x 3’ x 6’ 5" tent. Is there a hard and fast rule to how long the lights cycle should be on concerning auto flowers? I am growing with I presume Normal Veg cycle. 18 on. 6 off. But I would like to know, Can I get away with less light given its growth type?

Note: Just growing 1 Jack Herea? (Not sue how to spell that) That a friend gave me to try. It is still very small. Only about 4" But already has 3 or 4 very tight Nodes.
Thank you for any help! Especially those with much more knowledge than myself!


I run my lights 24 hrs on through seedling stage then once i start veg i go 18 on 6 off then flower i run at 12 on 12 off just like a photo. But ultimately its up to you i have seen people run them at 24 hrs of light i just believe everything grows better with sleep


im right there with you. i have not found consensus on this issue. best of luck

I see people who grow autos regularly and the best yields have been with 12/12 cycle. Thats why i opted to do 12 hr cycles.

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Thanks for the info Sirsmokes. But I’m really looking for some proof through testing and trial and error. Something documented. But it appears I’m not alone in this search. Can someone possibly point me in the right direction? A website perhaps?

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im watching this thread. i want to know too

Please do Miss/Mr Stealth. And if I find any information away from this thread, I’ll be sure to let you know. I’m just going to keep searching the internet. I know there is no lack of knowledgeable people on this site so that’s why I thought I would ask the light cycle question here also.
Thanks for any help

there are hardcore horticulturists who say plants must have at least 6 hours of dark. and there are abundant opinions that say 24 hours doesnt hurt and may benefit yield.

i really dont know. i have only one timer, its on a different project and i dont want another one. im too lazy to turn off the light every night, and i want maximum photosynthesis. so i use 24/0.

but once my hlg light comes in i may go to 18/6 or 20/4 because ill hopefully be maxing out the plants photosynthesis with a better light.

so heres a good question too. if the light is weak, like most blurples then maybe you want 24hours light, but with a more intense light maybe its better to have some dark cycle metabolism.

ill keep collecting info and fwd

@Screwauger he has an excellent write up on autos. Well worth the read.


Thanks @Familyman

I’ve used all variations of light schedules on my auto’s.
!st grow I went 20/4 throughout
2nd Grow was 20/4 then back to 18/6
3rd grow 16/8 throughout
Current grow 14/10

schizo-lightal personality! Frankly, I do not think it makes a huge impact but that’s from a guy that is growing way past his needs and doesn’t really need to analyze this factor at the moment (or I am stoned and lazy hahaha). I like more hours of light in veg overall as the way I grow auto’s is to maximize veg. Your results may vary.

That’s a good point. I think folks get to caught up in when they will flower vs trying to put on the most mass and budsites. With autos, you play on there time not yours.

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You really do, and I am still in the early to mid learning stages. I over-analyze stuff and have read way more than necessary about auto’s. This is because when I grew in the nineties, I was sheltered or at least knew nothing about feminized or landrace or autoflower strains. I grew great bagseed!!

These auto’s need all the care you can muster to NOT stunt or stall them in any way in the first 6-8 weeks. If your grow area is dialed in fairly well you can get an auto to decent sized in those 6-8 weeks! I can anyways.

I see nothing wrong with 24 hour light for the first week or two and then dial it back gradually to the schedule that works. Auto’s still gonna do what it does.

Disclaimer: I make no attempt to speak factually here, only my experience. There may be very real and necessary benefits to a canna plant getting a certain or minimum dark period for proper development. I didn’t get that far in my research when I was able to start smoking my first harvest I stuck with what worked.

I think your journal was a great read with a lot of information. It was one of the first ones I read here and even if you don’t realize it there’s many good points and ideas in it. Especially your feeding timeline. I’ve got that bookmarked and will be writing it on my planner when I get going soon. So scientific evidence? No but damn sure helpful advice for those of us getting started. So much so I’d recommend anyone getting started with autos to read it first.


Yep. That’s why I tagged the auto god!