420 Magazine Background

The Photoperiod


New Member
There has always seemed to be a debate on the vegetative photoperiod. Some growers swear by the 24/0 photoperiod while others feel that the 18/6 photoperiod better suits there plants. Personally, I like to use the 24/0 photoperiod.

I happened to be reading through my grow bible and came across some interesting information about the vegetative photoperiod particulary the last paragraph. There have been a few times I changed from 24/0 to 18/6 during the vegetative photoperiod. I guess I'll stop doing that. :smoke2:

The following information is straight from Greg Green's "The Cannabis Grow Bible"

Cannabis is a light demanding plant. Professional growers keep the light on their plants using the 24/0 photoperiod for this reason. Plants that grow under 24/0 flourish and do not need a quantity of darkness in order to rest and perform photosynthesis properly. Plants that are grown in optimal conditions under 24/0 light regime grow vigorusly and the benefits of a 24/0 photoperiod can be seen actively in the results. More nodes are formed, more branches are created, leaf numbers increase, the plant is growing at its finest.

Some growers opt to use 18/6 as their photoperiod. This is 18 hours of light, six hours of darkness light regime. Under these conditions the plant will grow quite naturally but not as vigorously as the 24/0 photoperiod.

The 18/6 photoperiod expels 3/4 the amount of light that a 24/0 photoperiod does. Although this does not mean that a plant produces 1/4 less leaves,branches and nodes under the 18/6 photoperiod, it certainly does show the correlation between light and cannabis growth. As we have said already, cannabis is a light demanding plant. There are no problems associated with 24/0 and although some have attributed cannabis sexual dysfunction (the hermaphrodite conditon) to 18/6 photoperiod these problems are actually the result of heat stress.

A 24/0 photoperiod requires that your grow room temperature be kept well monitored. The 18/6 option is cheaper to run. You use a quarter less electricity and this will have an impact on your electricity bill. Also the 18/6 photoperiod will generally extend the bulb's lifespan. During the 6 hours of darkness the grow room is allowed to cool down for this period but a well maintained good grow room setup should not require a cooling down period.

24/0 and 18/6 both share the same problem though. Once you start the photoperiod you should keep that way especially when the plants near maturity (the preflowering stage). An irregular photoperiod can cause more males than females to develop. It can also cause sexual dysfunction to appear. Whether you choose 24/0 or 18/6 as your vegetative photoperiod try to keep that photoperiod unitl your plants are mature enough to express their sex.


New Member
I do 24/0. ..


New Member
Figured I'd give this thread a bump. Even though I use feminized seeds I had a few instances in the beginning of my growing "career" where I had some hermaphodites. The only thing I've changed is my vegetative photoperiod. I use to run 24/0 for the first couple weeks then switch to 18/6 for the remainder of the vegetative stage. Since changing to straight 24/0 I have not had a single hermaphodite in my garden. Not sure if it's coincidence or not, but I figured it was atleast "BUMP" worthy.


New Member
First i've heard about lighting cycles affecting gender. Good to know. Im kinda fuckt by that info, seeming as im on my first grow and the lighting has been anything but constant. I fill the 18/6 but not in steady, uninterupted bursts and some days actually get more or less light due to security constraints. My lights are on a remote so i can turn them on and off and I am not using a timer. Only the remote.
Top Bottom