Best light schedule for growing autoflowers

The one glaring difference between autoflowers and regular photoperiod cannabis plants, is the need or lack thereof, of light schedules. As you may know, photoperiod plants require specific light schedules to begin flowering. Autoflowers, bred with cannabis ruderalis genetics, do not rely on light schedules to begin blooming. This benefit of autoflowering varieties is why so many beginner growers turn to these genetics, for ease of growth.

But, that doesn’t mean you won’t need a light schedule for autoflower plants. Some schedules will promote more optimal growth than others. So it’s key to understand autoflower light schedules in general. Especially, if you’re seeking to maximize your yields. Here we’ve put together the ultimate guide to light schedules for autoflowers. With this information, you can better decide which works best for your crop or operation.

How Do Autoflowers Grow?

Autoflowers grow differently than regular photoperiod plants, due to the cross-breeding of strains with ruderalis genetics. This lesser-known species is known for growing wild, and flowers without strict schedules of dark and light. Hence, their name and being ‘automatic’ in nature for growth. Like being on autopilot, autoflowering genetics switch from vegetation to flowering based on their age. Rather than relying on ratios of light to dark, like photoperiod plants.

Recommended Light Schedules for Autoflowers

Similar to other factors in growing, there’s much debate amongst growers on the best autoflower light schedules. While some stick to 24-hour light cycles, claiming autoflowers produce bigger yields without darkness…others think differently. The thought with using light schedules for autoflowers, is it gives the plant time to rest. Many growers believe rest helps plants grow healthier and therefore better. Without much proof on the topic, we set out to explore the most common autoflowering light cycles. From real-time experience of growers, here’s a breakdown of light schedules for autoflowers, you can choose to use.

24 Hour Light Schedule

The thought behind the 24-hour light schedule comes from the origins of the ruderalis species. The ruderalis species primarily comes from the northern parts of Russia. In this area, 24 hour sunlight is common. Leading many to believe that autoflowering varieties can thrive with zero periods of darkness. For growers, there’s a few pro’s and con’s to a 24-hour light schedule for autoflowers. Including –


  • Less work or equipment – With 24 hours of light, you won’t need to manually shut off lights every day. Or, buy extra equipment like a timer to do so automatically.
  • May maximize yields – The more light, the more energy right? Some growers claim this concept is true, and that 24 hours of light can potentially produce higher yields.
  • Better for cold climates – If your growing area is susceptible to temperature drops, due to colder climates than keeping lights on for 24 hours can help.


  • Increased electricity – Keeping your lights on 24/7 will obviously increase the amount of electricity used. When avoiding higher than normal electricity bills, 24 hour autoflower light schedules aren’t ideal.

18/6 Light Schedule

Some growers have settled on a compromise between standard 12/12 photoperiod light cycles, and 24-hours of light that autoflowers may be able to handle. This has produced the most commonly used light schedule for autoflowers, of 18/6. Or, 18 hours of light and 6 hours of darkness. This schedule, of course, has pro’s and con’s itself. Like the following factors to consider –


  • Provides rest – Many growers are adamant on plant’s receiving ‘rest’ to produce maximized yields and results. Periods of darkness are typically recommended for all plants, to encourage healthy growth without stress.
  • Less electricity – Even with just 6 hours of darkness, you can cut your electricity use (and costs) by 25%.
  • Better for hotter climates – No matter your location, but especially in hotter climates – there’s typically a ‘hot’ part of the day. To control your temperatures during this time, shutting the lights off for a 6-hour period, can help.


  • Requires a timer – When using an 18/6 light schedule for autoflowers, additional equipment like a timer will be required. Or, else you’ll be stuck manually shutting lights off at a set schedule or time, daily.

Other Light Schedules to Consider

18/6 and 24 hour light schedules aren’t the only autoflower light schedules to consider. Again, like most factors in growing, you’ll find a groove that works best for you or your plants. Along with forming your own preferences by trial and error. Since autoflowering plants can technically take up to 24-hours of light, a wide range of light schedules can work. Beyond the two most common, other light schedule examples include 22/2, 20/4, 19/5, and 16/8. Basically, any dark period will produce the same pro’s as 18/6 with differing dark periods for your own personal growing benefit.

What about 12/12 Light Schedules?

12/12 is the standard light schedule for photoperiod plants, to trigger the flowering phase. So, it begs the question – does 12/12 work for autoflower light schedules too? Not exactly. 12 hours of darkness is typically too much for autoflowers that can thrive with double the amount. The lack of energy often stunts growth, and produces much smaller plants. Meaning, smaller yields, too.

The 12/12 schedule is not recommended for autoflowering plants in general. But that doesn’t mean it’s not possible if necessary. For instance, if you’re growing both photoperiod and autoflowering plants, in a compact area, then you might have to use the same periods of darkness. In this case, your autoflowering plants will still grow, just at lesser yields than with longer periods of light.

Lighting up to Light Up

As you can see…like most practices in growing weed, it’s all about the personal preference or success of each individual grower, and crop. Deciding your light schedule for autoflowers will ultimately depend on your climate, electricity capabilities, and experience. If you’re just beginning to grow, use this information to best decide where to start. From there, you can easily adjust light schedules as you see fit along your growing journey.

2 Replies to “Best light schedule for growing autoflowers”

  1. Do Autoseeds need grow light or/and sunlight to grow, or can they grow under just a white light bulb ?

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