Last Updated: August 1, 2017

Definition - What does Photoperiod mean?

The photoperiod of a cannabis plant refers to how much lighting it should receive in 24 hours in order to produce the most yields. Cannabis plants require different photoperiods, depending on their stage of growth. Not all types of cannabis rely on photoperiods. Autoflowing strains, for example, don't rely on specific photoperiods in order to flower.

During the vegetative stage, photoperiod-reliant cannabis strains, as opposed to autoflowering genetics, are typically given either an 18/6 or a 24/0 light cycle/photoperiod, with the first number representing how many hours of daylight per 24 hours to provide, and the second number representing the amount of darkness hours per 24-hour period.

While they usually take longer to produce a usable yield (average of four months), photoperiod-reliant plants usually produce larger plants and yields.

Photoperiod cannabis strains will often produce a more potent bud than autoflowering genetics, although this fact is changing now that autoflowering genetics are becoming more refined.

Cannabis strains that rely on photoperiods tend to be able to withstand more abuse due to unlimited vegetation periods. These same strains respond well to topping and supercropping in the vegetative cycle.

MaximumYield explains Photoperiod

In biology in general, the physiological reaction of any organism to the length of the day and night hours it is exposed to is known as photoperiodism. Photoperiodism occurs in most plants and animals and can also be defined as the developmental responses of plants to the relative lengths of light and dark periods. Photoperiodism is of particular importance in cannabis cultivation, as growers wish to balance energy savings with boosting yields.

In terms of marijuana, during the vegetative phase, most professional growers follow a 24/0 photoperiod where they leave their lights on for 24 hours a day. It results in much more vigorous plant growth, thus producing a much more abundant yield. However, other growers opt for an 18/6 photoperiod. This means that the lights are on for 18 hours a day and off for 6.

While this is a quarter less than a 24/0 period, this does not cause the cannabis plants to produce a comparative quarter less weed. They certainly will not produce as much of a yield as a cannabis plant grown under 24/0 lighting, but it is in no way a comparatively disappointing amount.

The advantage of going with a light period of 18/6 is that your grow room requires less monitoring and you spend less money on electricity. A 24/0 photoperiod results in a more bountiful yield, but costs more in electricity and causes the grow room to get hotter as it will have no cooling down period. An 18/6 photoperiod, however, will not require this.

When plants reach the end of their vegetative phase, the photoperiod will be changed into 12/12. This triggers a reaction in the plant that causes flowering and this photoperiod is maintained until harvest.

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