Best light schedule for auto-flowering strains?

by Nebula Haze

Cannabis strains have two main stages of life, the vegetative (first) stage, and the flowering (second) stage. Think of them as the "children" and "adult" stages of marijuana growth.

Most strains of marijuana (photoperiod strains) rely on the amount of light, or their light schedule, to determine when to start making buds. Generally, if a marijuana plant receives 14 hours of light a day or more, it will stay in the vegetative stage (it will focus more on growing leaves and stems without any buds).

Auto-flowering strains don't rely on light schedules to determine when to flower. Auto-flowering strains will automatically start budding after about 2-3 weeks regardless of the light schedule they're given.

Wait! What is this about vegetative and flowering stages?

The Life of a Cannabis Plant

1. Vegetative - Seedling or clone leads to Vegetative Stage

2. Flowering - Flowering (Budding) Stage leads to Harvest

"Auto-Flowering" strains of cannabis have different light requirements that Photoperiod strains

Auto-flowering varieties of marijuana don't rely on a change in light schedule to determine when to flower. These strains (sometimes called "Lowryders") will finish their whole life cycle in two to three months, regardless of how much light they receive a day. The next question, then, is how much light to give auto-flowering or Lowryder marijuana plants if you are growing indoors? 

Most people seem to agree that the optimum amount of light to give is 18-24 hours of light a day for auto-flowering strains of marijuana. I have spoken with two people who have grown Lowryders personally and they have both told me that their auto-flowering plants seemed to do best when given 18-20 hours of light a day (as opposed to 24 hours a day). They both said that their plant's leaves seemed to be more green and healthy looking when given a 4-6 hour "dark period" every day. This obviously isn't a large sampling of people, but from what I've read on forums online, there does seem to be a general consensus among experienced Lowryder growers that 18 hours of light a day is best for auto-flowering strains. 

In contrast, many in-the-know people (such as Jorge Cervantes, who wrote  Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible) seem to agree that regular indica and sativa strains of marijuana get the most growth if given 24 hours of light a day when in the vegetative stage. I know that when I am growing indica, sativa, or hybrid strains of marijuana, I give them 24 hours of light a day during the vegetative stage and get great results!

Light Color Spectrum

Another consideration when growing auto-flowering plants is what light spectrum to use.

Normally you would optimally use more blue lights for the vegetative period and more red lights for your plant during the flowering period. With auto-flowering strains, you follow the same principle by using the blue lights before the plant has showed signs of it's gender, and then switch to more red lights once you see the first signs of gender.

Blue Light for Vegetative - bluish light (like from Metal Halide bulbs or 6500k (blue) fluorescents/CFLs) are a great choice for the vegetative stage (which for auto-flowers is just the first few weeks of life).

Yellow Light for Flowering - yellow/orange/red light (like from HPS bulbs or "soft white" colored CFLs/fluorescents) tend to produce the best growth and densest buds in the flowering stage. Their color mimics the reddish light from the autumn sun. 

HPS grow lights are the most popular grow light for the flowering stage, with good reason. They are one of the most efficient grow lights available today (as far as electricity used for density/yields produced - even more efficient than most LED grow lights), they're cheap to start with, they're just the right color spectrum for optimal flowering, and they're more standardized and intuitive to use than many other types of grow lights. Learn more about finding the right size HPS for your space

However, marijuana plants are weeds, and will usually grow at least okay under either spectrum of light during either stage.

Light in any color spectrum will produce good growth and bud as long as you're using cannabis grow lights and there's enough brightness.

In fact, many growers use Metal Halide or other more "blue" colored lights for the entire life of the plant, and still produce good results. Some growers even prefer these lights for budding. 

But the best results in flowering are acheived by reddish-yellow light. For the hobbyist grower who may be low on cash and can't change up the lights, you may want to consder getting all flowering bulbs for autos since they spend practically their whole life in the flowering stage. 

Learn more about auto-flowering strains