Autoflower Cannabis Light Schedules

Autoflower Cannabis Light Schedules

To understand autoflower cannabis light schedules, let’s first look at the daily life of a cannabis plant.

Cannabis plants take in carbon dioxide and light during the day to create chlorophyll while releasing oxygen as a by product.  This is photosynthesis and it can only happen during daylight hours. With no light the photosynthesis process doesn’t work. During photosynthesis the plant is respiring, or breathing, just like you or I.  At night, with no light, the cannabis plant continues to respire. If it stops respiring, or breathing, it dies just like a human. It also breaks down chlorophyll into carbohydrates, energy or food, which it stores for later use.

Autoflowering cannabis plants do not need darkness. Autoflower plants are not dependent on changes in the light schedule to commence flowering.  This is why they can be grown using a light cycle of anything from 12 to 24 hours daily. This is also what makes them perfect for first time growers as light periods are one less thing to worry about.

So what amount of light is ideal?  Let’s look at the 3 most popular light schedules:

Most Popular Cannabis Light Schedules

24/0 – This is light on all day and night.  The plants never see darkness. Many growers use this method and report great results.  They believe that the extra size of the plants will increase the yield and offset the higher electric costs.

However there can be issues with this as cannabis plants prefer to eat in the dark.  When you leave cannabis plants under a 24/0 light schedule you are forcing the plant into creating the chlorophyll AND converting the chlorophyll into carbohydrates at the same time.  This can lead to plants that have health and/or stress issues. And there is no evidence proving that 24/0 light schedules produce higher yields than 18/6 or 20/4 light schedules.

18/6 – This is the most common light schedule as it tries to mimic the amount of light a plant would get at the height of summer in the northern latitudes.  Thus while pushing the plant a bit, 18/6 falls within the normal tolerances of most cannabis plants because it is simply replicating real life conditions. The 6 hours of darkness allows plenty of time for the plant to convert chlorophyll without the need of having to photosynthesize simultaneously.

20/4 – This is a light schedule becoming more popular, especially for autoflower cannabis.  Since autoflower cannabis plants are a ruderalis cross, and ruderalis grows in the very north of Russia where there are nearly endless summer days, most autoflower strains are receptive to longer days, and thereby more light.  The 4 hours of darkness still gives the plant enough rest to keep it healthy while pushing growth to the maximum.

12/12 – 12 hours on, 12 hours off is the light schedule for flowering feminized cannabis.  Non autoflowers require 12 hours of darkness each night in order to stay in flowering stage.  Flowering plants can revert back to vegetative if they sense light for more than 12 hours. This is the reason tents are needed for indoor growing.  Keeping the plants in the dark, unaffected by indoor light, is the main reason for a tent or the use of a closet. Flowering cannabis by putting it in a main room near a window is a perilous risk. 

6/2 x 3 – This is a newer light schedule that doesn’t have a lot of history..  In 6/2 x 3, daily light runs on a 6 hours on, 2 hours off schedule that is repeated three times a day.  A little simple math shows that the end result is 18/6, but it is simply broken down into 3 shifts. The theory here is that by letting the cannabis plant nap 3x a day as opposed to sleep once, you avoid most kinds of light/heat induced issues and maintain a more normalized temperature.

Thus, light schedules for autoflowering cannabis plants are really easy to grasp.
All you have to do is keep the light turned on 18-20 hours a day.  Giving 18-20 hours of light is crucial when growing autoflowering plants, as it gives them the best chance to grow bigger in the vegetative stage, and bigger buds during flowering.  

With all that being said, setting light schedules is not the ideal way to measure the correct amount of light to give your cannabis plants.  The best way is to understand moles. Not moles as in the little furry creatures ruining your garden, but moles, the measure of unit for light intensity.