Autoflower light cycle. 24hr vs 18/6hr

neneboob · Mar 17, 2025

Recently decided to try a few auto flowers, and when I first started I got a good bulk of my information on growing autoflowers from a youtube channel. They only did auto's and they kept their light on 24 hours a day. Seemed like a good idea at the time, but now I've seen a lot more of a debate between 24hr light or 18hr on and 6 off.

Literally EVERYTHING I read seems to be contradictory.

Can anyone help me parse what's "Bro-science" and what's actually factual information?

Anyone have experience that has cemented their opinion on the auto light cycle?

RegularRebel · Mar 17, 2025

Day neutral plants, like your hemp hybrids, still need a skotoperiod for optimal health. Without it they get stressed. If you want science, grow some under 24 hours DLI, and the others under 16 hrs DLI. See which is healthier. Anything over 16 hrs of intense light is just a waste of electricity due to photoprotection mechanism and is not ecologically friendly or responsible growing practice. Dries out soil faster, using more water, etc. The only people that want you to run your lights 24hrs a day is the people you pay for electricity, and the light manufacturers who want you to wear out your equipment faster so you buy the next one, and the people selling you remedy products because you followed. Imitated without knowing what and why.

Instead of watching cannabis botany bs on youtube, study gardening, horticultural science, and avoid all cannabis specific focused information because it's so bad, it's easier to avoid it altogether than to filter out the mountain of garbage that looms in front of you. Studying basic gardening, plant biology and so on will be a quantum leap in your understanding.

neneboob · Mar 17, 2025

RegularRebel said:
Day neutral plants, like your hemp hybrids, still need a skotoperiod for optimal health. Without it they get stressed. If you want science, grow some under 24 hours DLI, and the others under 16 hrs DLI. See which is healthier. Anything over 16 hrs of intense light is just a waste of electricity due to photoprotection mechanism and is not ecologically friendly or responsible growing practice. Dries out soil faster, using more water, etc. The only people that want you to run your lights 24hrs a day is the people you pay for electricity, and the light manufacturers who want you to wear out your equipment faster so you buy the next one, and the people selling you remedy products because you followed. Imitated without knowing what and why.

Instead of watching cannabis botany bs on youtube, study gardening, horticultural science, and avoid all cannabis specific focused information because it's so bad, it's easier to avoid it altogether than to filter out the mountain of garbage that looms in front of you. Studying basic gardening, plant biology and so on will be a quantum leap in your understanding.

I have to agree that a lot of the cannabis focused content is far from scientific.

As much as I'd love to do my own experiments I've only got 1 closet to grow in right now, so I'm hoping to learn from someone else can share their experiences.

Thanks for the detailed comment.

LoveGrowingIt · Mar 17, 2025

I'm of the same opinion as @RegularRebel.

It may help to consider that plants evolved with both day and night, so they know what to do with each. During the day, they photosynthesize nutrients (sugars). Some of those nutrients are used and others are sent to the roots and stored for use during the night, because photosynthesis does not occur in darkness. The stored nutrients enable the plants to grow during the night. Sometimes it's even possible to detect how much they've grown during the night, especially during their active growth stages of life. (They certainly don't rest.)

I'm not sure what the additional light does for plants, other than work against their natural tendencies. Growers who use 24/0 lighting claim it works for them. Autoflower plants do seem to like plenty of light. However, I use 18/6 for my autoflower plants and I'm not complaining about the results. It could be there's a tradeoff. Thus, if there is more growth under 24/0 light, is it enough to warrant the additional cost of running the light? My thinking is that it does not--for my purposes, anyway.

LoveGrowingIt · Mar 17, 2025

Also... Welcome to the farm!

RegularRebel · Mar 17, 2025

neneboob said:
I have to agree that a lot of the cannabis focused content is far from scientific.

As much as I'd love to do my own experiments I've only got 1 closet to grow in right now, so I'm hoping to learn from someone else can share their experiences.

Thanks for the detailed comment.

When you learn plant biology, you will learn which cells do what, when. So what happens during skotoperiod will be understood and what lack of a skotoperiod results in.

I did a quick search since you like youtube (watch ad free youtube videos with grayjay app)

Here is an example of an experiment with DLI at early growth phase like you are at.

RegularRebel · Mar 17, 2025

I dont grow hemp hybrids because the effects are weaker and wear off so quickly, after a half hour or so, but this is how it works best for my marijuana plants: Seedling: 16 on 8 off. Vegetative: ( varies) same as seedling if I want taller stemmy plants, but also I can go down to 14, or 12 if I want more compact bushy plants with shorter internode spacing. If I do 12, then I interrupt the dark period in the middle with 1 hour light to keep them in vegetative growth and prevent flowering. 30 minutes is enough, I just use 1 hour to be sure. As for hemp hybrids, I am no expert. Tried it once and will not repeat that experience. Total let down as far as end user experience. Looked pretty though. So there is that positive gardening and visual experience that can be had with them.

neneboob · Mar 17, 2025

RegularRebel said:
I dont grow hemp hybrids because the effects are weaker and wear off so quickly, after a half hour or so, but this is how it works best for my marijuana plants: Seedling: 16 on 8 off. Vegetative: ( varies) same as seedling if I want taller stemmy plants, but also I can go down to 14, or 12 if I want more compact bushy plants with shorter internode spacing. If I do 12, then I interrupt the dark period in the middle with 1 hour light to keep them in vegetative growth and prevent flowering. 30 minutes is enough, I just use 1 hour to be sure. As for hemp hybrids, I am no expert. Tried it once and will not repeat that experience. Total let down as far as end user experience. Looked pretty though. So there is that positive gardening and visual experience that can be had with them.

Wow this video is honestly exactly what I was looking for thank you very much. I apricate you sharing your experience with me. I guess I really need to rethink the way I've been researching it's nice seeing facts and evidence based assertions instead of "nah bruh trust me"

RegularRebel · Mar 18, 2025

neneboob said:
Wow this video is honestly exactly what I was looking for thank you very much. I apricate you sharing your experience with me. I guess I really need to rethink the way I've been researching it's nice seeing facts and evidence based assertions instead of "nah bruh trust me"

That is the right attitude, seeking facts. The other part is not to fall into the products trap. Again here many ordinary gardening products are the best for your garden and wallet.

Please help others with what you have learned.

A change in popular cannabis culture is inevitable, but the sooner we move away from the bs, the greed, marketing, and exploitation, superstition, belief, lies, the silencing of facts and opinions that dont align with the sponsors or popular belief, the better. Who knows, maybe soon we all will be meeting up in a gardening forum and websites like this will be left to unthinking imitators and get a reputation they have worked towards through their own bad decisions.

Grownsince95 · Mar 18, 2025

The reason why some auto growers use 24 hr light cycles is because autos are bred from Ruderalis varieties. In the wild these plants grow around or above the Arctic circle. As we all know this is the land of the midnight sun, where there is no night during summer. To an auto it's perfectly normal.

The reason you see so much conflicting information is because there really is no black and white answer to your question. Plants will definitely grow under 24 hrs of light, even the photoperiod ones. Do they like it? Idk you have to ask them!

I use 24/7 for clones and if I ever have to re-veg. But the reason I use it for clones is for the consistency in temp and humidity, not the lack of dark period.

I am a believer that most plants do indeed benefit from a dark period. Not to make it more confusing but I run my autos and veg photos on a 9/3 on/off to manipulate the DLI. 6/2 seems to be gaining some traction with the auto folks too. If you want I can elaborate on my experience with this and why I made the change.

RegularRebel · Mar 18, 2025

Grownsince95 said:
The reason why some auto growers use 24 hr light cycles is because autos are bred from Ruderalis varieties. In the wild these plants grow around or above the Arctic circle. As we all know this is the land of the midnight sun, where there is no night during summer. To an auto it's perfectly normal.

The reason you see so much conflicting information is because there really is no black and white answer to your question. Plants will definitely grow under 24 hrs of light, even the photoperiod ones. Do they like it? Idk you have to ask them!

I use 24/7 for clones and if I ever have to re-veg. But the reason I use it for clones is for the consistency in temp and humidity, not the lack of dark period.

I am a believer that most plants do indeed benefit from a dark period. Not to make it more confusing but I run my autos and veg photos on a 9/3 on/off to manipulate the DLI. 6/2 seems to be gaining some traction with the auto folks too. If you want I can elaborate on my experience with this and why I made the change.

What's your source of information on breeding? Not asking for scientific proof, just wondering. Not that I think Todd is a reliable source, he actually seems confused, or sarcastic....but has actually started to make me question the narratives I have come across anyway. Todd talking crap, but I think he means Fiona, not Fiola: https://www.thcfarmer.com/threads/m-from-todd-mccormick-on-autoflowering.167486/

People I've spoke to personally, with a lot more credibility and experience than Todd say autohemp is a cross between (drug plant) cannabis indica and cannabis ruderalis (edible hemp). Of course back crossed several times with drug plants to get the THC up to about 8-10% but still retain the day neutral trait.

RegularRebel · Mar 18, 2025

RegularRebel said:
What's your source of information on breeding? Not asking for scientific proof, just wondering. Not that I think Todd is a reliable source, he actually seems confused, or sarcastic....but has actually started to make me question the narratives I have come across anyway. Todd talking crap, but I think he means Fiona, not Fiola: https://www.thcfarmer.com/threads/m-from-todd-mccormick-on-autoflowering.167486/

People I've spoke to personally, with a lot more credibility and experience than Todd say autohemp is a cross between (drug plant) cannabis indica and cannabis ruderalis (edible hemp). Of course back crossed several times with drug plants to get the THC up to about 8-10% but still retain the day neutral trait.

outside of self promotion and self elevating, Todd is trying to usher in a new mythology perhaps.

Grownsince95 · Mar 18, 2025

RegularRebel said:
What's your source of information on breeding? Not asking for scientific proof, just wondering. Not that I think Todd is a reliable source, he actually seems confused, or sarcastic....but has actually started to make me question the narratives I have come across anyway. Todd talking crap, but I think he means Fiona, not Fiola: https://www.thcfarmer.com/threads/m-from-todd-mccormick-on-autoflowering.167486/

People I've spoke to personally, with a lot more credibility and experience than Todd say autohemp is a cross between (drug plant) cannabis indica and cannabis ruderalis (edible hemp). Of course back crossed several times with drug plants to get the THC up to about 8-10% but still retain the day neutral trait.

I've been growing and breeding for 30 years.

That guy is severely misinformed. Ruderalis cannabis has been described and written about by actual scientists since at least 1924. To say he discovered it with Nevil on the side of the road in the 70s is the most arrogant bullshit I've ever heard.

Don't forget to like and subscribe though!

Grownsince95 · Mar 18, 2025

Finola is the first deliberately bred auto flower. Made from Russian Ruderalis plants in the 90s. Read more and listen to talking heads less.

RegularRebel · Mar 18, 2025

Grownsince95 said:
I've been growing and breeding for 30 years.

That guy is severely misinformed. Ruderalis cannabis has been described and written about by actual scientists since at least 1924. To say he discovered it with Nevil on the side of the road in the 70s is the most arrogant bullshit I've ever heard.

Don't forget to like and subscribe though!

I agree totally. But I haven't personally read anything about ruderalis hemp from the reliable sources, like chandra and such. Just not interested to be honest. It's not my medicine.

I think the real answer lies in testing. Even if it is a home-test, just as the above video, but with several day neutral plants, one of which should be ruderalis hemp. Then we would have at least an indication of an answer. Until then it's more guesses. "Bro science" like the original neneboob wants to avoid. Hence my response, test it.

TheGoldenRoad · Mar 18, 2025

Grownsince95 said:
The reason why some auto growers use 24 hr light cycles is because autos are bred from Ruderalis varieties. In the wild these plants grow around or above the Arctic circle. As we all know this is the land of the midnight sun, where there is no night during summer. To an auto it's perfectly normal.

The reason you see so much conflicting information is because there really is no black and white answer to your question. Plants will definitely grow under 24 hrs of light, even the photoperiod ones. Do they like it? Idk you have to ask them!

I use 24/7 for clones and if I ever have to re-veg. But the reason I use it for clones is for the consistency in temp and humidity, not the lack of dark period.

I am a believer that most plants do indeed benefit from a dark period. Not to make it more confusing but I run my autos and veg photos on a 9/3 on/off to manipulate the DLI. 6/2 seems to be gaining some traction with the auto folks too. If you want I can elaborate on my experience with this and why I made the change.

I’ve been reading a lot about revegging recently and was curious if a 24 hour light cycle for the first couple weeks would help.

RegularRebel · Mar 18, 2025

TheGoldenRoad said:
I’ve been reading a lot about revegging recently and was curious if a 24 hour light cycle for the first couple weeks would help.

Because of plant biology, I would say no it wouldnt help. Photoreceptors phytochromes and cryptochromes dont just regulate growth patterns for switching to flowering but also have a purpose in vegetative stage. One of which is cellular repair. You can find out what how and why by researching plant biology. Once you do that you will forget about this 24 hour light stress nonsense. Cannabis (excluding ruderalis hemp) is a SHORT day plant / LONG night plant. It loves darkness, but needs light. You got it backwards in your thinking. When you start elongating the skotoperiod the plant blossoms, flowers, gets happy. Its happy in the dark. Do you have space to do a test? Say 4 and 4 samples?

RegularRebel · Mar 18, 2025

Grownsince95 said:
I've been growing and breeding for 30 years.

Now I understand why I enjoy your replies on the topics people post. They make sense.

There is more questions than answers and people are remaining dumb because nobody is willing to do even an informal test in search of truth. It's no wonder people just guess at what idea they are going to try next. It's sad to see people groping in the dark. There isnt anyone really willing to do the work. Not even a 30 year experienced gardener knows because they haven't tested it. Their interest and time has gone in some other direction. The people asking should be finding out rather than expecting to be handed an answer. But they think that by now, somewhere, someone has done a valid test. But it doesn't seem like anyone can find that information. I wont grow autohemp. So I'm not going to be a help in this matter beyond what I have attempted already.

Someone please step up. Do a valid test honestly. And post the results in a way people can find it by searching.

TheGoldenRoad · Mar 18, 2025

RegularRebel said:
Because of plant biology, I would say no it wouldnt help. Photoreceptors phytochromes and cryptochromes dont just regulate growth patterns for switching to flowering but also have a purpose in vegetative stage. One of which is cellular repair. You can find out what how and why by researching plant biology. Once you do that you will forget about this 24 hour light stress nonsense. Cannabis (excluding ruderalis hemp) is a SHORT day plant / LONG night plant. It loves darkness, but needs light. You got it backwards in your thinking. When you start elongating the skotoperiod the plant blossoms, flowers, gets happy. Its happy in the dark. Do you have space to do a test? Say 4 and 4 samples?

Not at the moment but possibly in the future. I’m using a Tuff Shed and one of my projects this summer is going to be building a partition to separate it into two rooms. Right now all the bambinas are one big happy family.

Grownsince95 · Mar 18, 2025

RegularRebel said:
Now I understand why I enjoy your replies on the topics people post. They make sense.

There is more questions than answers and people are remaining dumb because nobody is willing to do even an informal test in search of truth. It's no wonder people just guess at what idea they are going to try next. It's sad to see people groping in the dark. There isnt anyone really willing to do the work. Not even a 30 year experienced gardener knows because they haven't tested it. Their interest and time has gone in some other direction. The people asking should be finding out rather than expecting to be handed an answer. But they think that by now, somewhere, someone has done a valid test. But it doesn't seem like anyone can find that information. I wont grow autohemp. So I'm not going to be a help in this matter beyond what I have attempted already.

Someone please step up. Do a valid test honestly. And post the results in a way people can find it by searching.

That's the thing about experience, I don't have to test it. I know what works now.

That's why new growers come here. To learn from people who've done it before. Who the hell has the time or space to go experimenting like you suggest?

Did you learn math by just playing around with numbers until it made sense? No, you had a teacher.

Autoflower light cycle. 24hr vs 18/6hr

Autoflower light cycle. 24hr vs 18/6hr

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Autoflower light cycle. 24hr vs 18/6hr

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