Autoflower light cycle and spectrum


A question from a fellow grower;

My question was can you change the light cycle on autoflowers and do you change light spectrum when autos flower


The answer to your question is yes!
You give no info on your grow so I will not speculate.
So I’m giving you this link it has everything you need too know about lights and. Auto plants.
Hope this helps

B Safe


Sorry Will…

No. You cannot change the photo period when growing autoflowers, unless you need to finish the plant due to time limits or emergencies.

You can grow then at any photo period, but should keep it consistent throughout grow. I am using 18/6 this time to see how well plants do.


Oh ok so you stay at a constant 18/6 from seedling throughout flower or 20/4
18/6 being best.



From what I’ve read, the ideal might be somewhere between 20/4 and 16/8. The exact ideal might be dependent on strain. It seems less light per day than 16/8 and yeild suffers, and more than 20/4 and yeild again suffers.

For what it’s worth,



At that link I left he suggests 24/0 throughout the grow for better results in growth and yield.
When I said yes, in my mind I was thinking of the different light allotments to choose from. But I fully understand how the plant should be raised.
It seems quite simple, but then nothing is ever easy or simple…lol



I read that exact same article on some other website once upon a time.

And I used to argue for 24 hour light schedules as C3 plants can’t really uptake CO2 during the dark and so they aren’t really doing much at all during the dark period and partially because of this article, but my recent above statements come from a lot more reading since then, as well as partially from Latewood’s recommendations and my own personal observations.



I was thinking the same thing when he spoke about the plant working while in the dark. Didn’t make any sense to me. I remembered reading what you had wrote about plants resting while in the dark and what you had wrote made a lot of sense to me and has stuck with me. That was the only thing I didn’t agree with when I read it.



Hi- I just saw all your comments about the light cycles of autos & wondering now if I did right by switching to 20/4 after raising them on 24/0 since germination. They seem to be doing ok (66 days old) hoping to finish them up soon but they really look like maybe a few more wks. lots of white pistils still on the lower branches.


18/6 or 16/8 better for yields than 20/4 or 24/0 …?


Longer photo periods do not equate to more yield in general. This may be different for Autos.

Thanks MacG for some great info.

You can use any photo period. I said I use 18/6 currently, because I am experimenting in order to give you all the correct info. I am also planning on starting Fem OG Ksuh in the middle of the finishing of these Autos. I need an 18/6 period for the OG; So, I am using 18/6 for the Autos. Now I can start my OG without worrying about the photo period. :slight_smile:


That’s a smart move. In your experience with auto plants. Finish time versus fem on average would be about how much time saved?



I will write you up my exact plan, and share it with you. But; It will have to be later on. My back went out after I tore a muscle or tendon in my thigh, and groin area. IN a lot of pain.

I will try to get to it later today when the pain evens out after the tylenol and flexeii kick in. Peace :slight_smile:


Hey Late, take your time my friend. I know, I did the very same thing all not that long…no fun at all.
You take care of that first!