The Best Light Schedule for Autoflowers

Autoflowers are every cannabis grower’s dream. They are easy to grow, most are resistant to common biotic and abiotic factors, grow from seed to maturity within a record time of 7-12 weeks, and can be grown multiple times a year.

The one feature that distinguishes them from photoperiodic strains is their ability to transition from the vegetative to the flowering stage without needing darkness. They automatically transition within 20-28 days after germination. Because they are not photoperiod plants autoflowers can grow under almost any light cycle, each with their pro’s and con’s. However what is the best light schedule for autoflowers?

If you are a novice grower or it’s your first time cultivating an auto strain, this autoflower light schedule guide will help you attain impressive yields within record time. It comprehensively covers four of the most popular light cycles for autoflowers and some vital tips that will take your cultivation game a notch higher. Let’s begin…

Most common light schedule for autoflowers – 18/6

‘18’ refers to the hours the auto plant gets exposed to light, while the ‘6’ applies to the dark hours. This is the most prevalent light schedule for autoflowers among cannabis cultivators since it allows the plant to have a 6-hour rest after 18 hours of making dense and appealing buds. The resting period facilitates healthy plant growth while still saving on electricity costs. This cycle is best-suited in areas where the climate is hot during the day. A grower can turn the lights off during the 6 hours when the temperatures are soaring high. 

Second most common light schedule for autoflowers – 24/0

Some cultivators believe that a 24-hour autoflower light cycle improves the yields exponentially. While this may or may not be true, this schedule’s downside is that it leaves no room for the plant to rest. A 24/0 autoflower light cycle is perfect in areas where the weather is too cold as it will keep them warm, especially during the night. The constant light exposure leads to faster growth, and the plant is likely to reach maturity a week or two earlier. However, one can expect a very high power bill. 

The debate between which is better between the 18/6 and the 24/0 is nearly impossible to settle. This is because both light cycles have been known to produce their fair share of impressive yields. As a new grower, the best option is to try out both schedules to figure out which works for your selected strain. 

Middle ground autoflower light schedule – 20/4

The 20/4 autoflower light cycle acts as the middle-ground between the 18/6 and the 24/0 light schedules. Here, the plant gets light for 20 hours and rests for 4 hours. It provides optimum growing conditions for the plant without the excess power bill. 20/4 is a relatively new schedule that many growers have gradually come to incorporate into their cultivation journey. The yield produced is quite impressive. 

Not so popular autoflower light schedule – 12/12

The 12/12 light schedule is used primarily when cultivating photoperiodic plants and thus does not work out well for their autoflower counterparts. For an auto plant to thrive health wise and produce bountiful harvests, it requires not less than 14 hours of light in a day. With this minimal light exposure, you can expect small plants and below-average yields. 

Light ScheduleWhen to useBest for
12/12The 12/12 light cycle is used to trigger flowering when growing with photoperiodic strains. It should not be used with autoflowers.Photoperiods
18/6The 18/6 light cycle is used autoflowers and also for photoperiodic strains during the vegetative stage.Autoflowers and photoperiods
20/4The 20/4 light cycle can also be used for autoflowers, some growers opt for this instead of 18/6 as it provides more light.Autoflowers
24 hours lightThe 24 hour light schedule is only used for autoflowers. Some growers opt to use this instead of 18/6 or 20/4. However, the constant light and heat provides no recovery time for plants so can cause stress.Autoflowers

While it is uncommon for cultivators to expose their autoflower plants to minimal light, the instances highlighted below might be the root cause;

Combined cultivation of photoperiodic and autoflower plants

As mentioned above, photoperiodic plants thrive when subjected to a 12/12 light cycle.  Growing autoflowers alongside these plants means that the autos will be exposed to less-than-ideal hours of light. 

High temperatures

Heat stress can negatively affect the growth of any cannabis plant. Consequently, cultivators living in hot climates may opt to switch the lights off during the day to avoid an overheated grow space. 

Minimizing on cost

The cost of electricity is very high, and maintaining an 18/6, 20/4, or 24/0 might take a toll on a grower’s finances. To cut down the overall cost, one may decide to try the 12/12 autoflower light schedule. 

Do autoflowers need darkness

Technically autoflowers can grow without darkness and in many regions where ruderalis grows in the wild there is little or no dark period, hence why they have adapted to flower regardless of light. However, for autoflowers to thrive they do need a dark period where they can rest and recover. Therefore the best light cycle for autoflowers is 20/4 or 18/6 as these provide enough light whilst still allowing recover time.

In short, to answer the question, ‘do autoflowers need darkness?’. No they don’t, but if you want to get the best out of your plants and produce good quality big yields it is highly recommended.

Tips on getting the best from autoflower plants

Use the best light for autoflowers – LED

During the vegetative stage, auto and photoperiodic plants are best exposed to 6000K blue spectrum light. This allows them to grow leaves, branches, stems, and roots that will ultimately help to hold the buds in place until harvest. Fluorescent lamps and specific LED lights are ideal within the first two weeks after germination since the plants are fragile. 

When the plant enters the flowering phase, a 2700K red spectrum light is recommended. HPS and top-notch LED grow lights provide the preferred spectrum of red light. 

While you can successfully grow autoflowers under any decent grow lights, the best light for autoflowers are LED because they cover all light spectrums, give of very little heat and consume less energy than most other grow lights.

defoliating autoflower cannabis plants

RELATED ARTICLE – Is It Okay To Defoliate Autoflowers?

Defoliation is a yield boosting technique, but can you use it when growing autoflowers?


The Sea Of Green technique involves a tightly packed canopy of nuggets. This is achieved by putting a   reasonable number of auto plants per square meter and forcing earlier bud development. SOG is perfect for cannabis businesses and growers looking to have multiple harvests per year within a short time while still working with limited space. This technique leads to better yields, proper utilization of resources, rapid growth, and proper light distribution. Within a square meter, we recommend growing a maximum of 7 plants in 7 liters to 10 liters containers. 

Sea of green autoflower grow under 20/4 light cycle indoors

Growing medium 

Autoflower plants do not respond well to repotting; thus, a grower needs to ensure that they plant the seedlings in a reasonably large container. Additionally, the growing medium needs to be well aerated to allow the free flow of air. 

Take away 

When it comes to autoflower light schedules, it is hard to pinpoint one cycle and label it as the best. Each grower has specific needs that can be fulfilled by one of the schedules highlighted above. Therefore, the best option is to try out each of them until you find the one that suits your particular needs to a tee. Let the climate of your growing area, electricity cost, and resources be your guiding factors. 

Personally our breeders consider 20/4 the best light schedule for autoflowers because it provides the most amount of light whilst still allowing a much needed 4 hour rest period which helps a plant to recover and grow, which could be best for any beginner growers. That being said many established growers do use 18/6 and 24 hour light cycles successfully. 

Our top rated autoflower strains

Big bud is the highest yielding strain

Big Bud AutoHighest yielding Autoflower strain

An indica dominant hybrid cross of Big Bud and a ruderalis. Big Bud Auto can produce yields unmatched by any other autoflower strain of around 500g/m2 and THC of up to 17% she is an ideal strain for any cash croppers.

Gorilla Glue 4 Feminized Seeds

Gorilla Glue AutoflowerHighest THC Autoflower strain

A potent hybrid Gorilla Glue Auto has some powerful genetics and even the autoflowering version can produce THC up to 25%.  Ideal for any experienced smokers that are after quick results and huge potency. Be sure to have a few pairs of scissors on hand for when you trim

Northern Lights Autoflower Seeds

Northern Lights Autoflower Best performer in cold conditions and lowest smelling strain

Indica dominant cross of Northern Lights and a ruderalis Northern Lights Autoflower is a fast flowering autoflower that will yield around 300g/m2 with THC levels of 12-15%. Ruderalis strains are native to the cold regions of Siberia and this has been crossed with the indica genetics of Northern Lights that are native to the cold mountainous regions of Afghanistan. Thanks to its indica and ruderalis genetics combined Northern Lights Autoflower is a hardy strain that can grow well in colder conditions. Northern Lights Autoflower is also a low smelling plant making it one of the best hybrid strains for any stealth grows.

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