Autoflower Light Cycles

Everything autoflower

Autoflower Light Cycles

bud photo from an autoflower

While it is standard practice with photoperiod grows to run the vegetation stage lights at 18 hours on and 6 hours off, with flowering running at 12 on and 12 off, autoflowers are more flexible in their schedules and do not need to be adjusted between veg and flower.

Since autoflowers don’t need to change their lighting schedule between vegetation and flower, most growers will run the same schedule from start to finish, though the exact cycle differs between growers. The four most common cycles to run autoflowers at are:


These cycles come with their own pros and cons and deciding which light cycle to use comes down to how important running costs are to you, whether heat is an issue in your tent and whether or not you’re running them in their own tent or with photoperiods.

We’ll take a look at each of these common light cycles and break down the subsequent implications of running your plants with them.

24 Hours on 0 Hours off – No Rest, All Work

The 24/0 cycle is a surprisingly common option among auto growers. This cycle leaves the lights running constantly, offering no rest for your girls, and instead focuses solely on pumping them with as much light as possible to increase growth. There is some debate between growers as to whether or not autoflowering plants require that downtime of darkness, as they naturally occur in higher latitudes and are genetically accustomed to longer periods of light. With that said, it’s not only the light itself that comes into play here as this cycle comes with the highest electricity cost, as well as the most heating inside your tent. If you do decide to run at 24/0, you will need to ensure you have good extraction and intake into your tent, and possibly air conditioning as well.

20 Hours on 4 Hours off – A Compromise

The 20/4 cycle is a personal favourite of mine, and what I tend to run my autos at. It offers 2 hours of additional light from the standard 18/6, to aid in growth, while still allowing for some rest period for the plants. Not only do the 4 hours of down time mean rest for the plants, but it also means 4 hours less electricity cost each day, as well as a period for your tent to cool down a bit.

18 Hours on 6 Hours off – A Safe Bet

The standard 18/6 cycle still remains extremely popular in autoflower grows, it offers what is considered a tried and tested cycle, offering a fairly large rest period, which cuts both temperatures and electricity costs, while still providing you with enough light to get good yields. Some comparisons have suggested that the 20/4 cycle may pull slightly more (5%-10% or so), but this is mostly anecdotal. If you’re new to autoflower growing, you may wish to begin with this cycle. Another useful part about an 18/6 cycle, is that you can easily run your autoflowers in the same tent as vegging photoperiod plants without having to adjust light cycles at all.

12 Hours on 12 Hours off – A Last Resort

You’ll want to avoid a 12/12 cycle if possible. Autoflowers are more than capable of producing good flower at this cycle, but you will definitely be hurting your yields. Autoflowers are all about that light and with a 12/12 cycle, there just isn’t enough of it to utilize all your plant’s potential. So why would you run at 12/12? Well, mostly 12/12 grows are done due to extra space in the photoperiod flowering tent. If you have access to some cheap autoflower genetics and some free space in your flowering tent, it certainly makes sense to throw a couple in there. Your yield may half in cases, but it can still be a worthwhile exercise.


In the end, it’s up to you to decide how you want to run your plants. What is your setup like? Is electricity cost an issue? Do you want to risk it for some extra yield, or do you want to play it safe? We’d recommend the 18/6 or 20/4 cycles for new growers as these tend to be the best combination of all factors. You could even do a 19/5 if you really wanted to.

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