Forcing Cannabis to Flower

What causes cannabis plants to flower? By controlling light and dark periods, you can manipulate when your plants flower. Learn about cannabis photoperiodism and how you can use it to your advantage.
July 18, 2022

What causes cannabis plants to flower? Any successful cannabis cultivator must know the answer to this question in order to generate revenue from a crop. Alternatively, the reverse knowledge, how to prevent cannabis plants from flowering, must be used to keep a Mother plant in a perpetual veg state.

The answer is simple and lies in the biological makeup of the cannabis plant. Cannabis plants will flower when they receive more than 12 hours of continuous darkness. This is known as a short-day plant.

Cannabis Photoperiod

To understand this better, let’s look at the science behind photoperiodism, or the reaction of organisms to the length of day or night. There are two main types of plants: long-day plants and short-day plants.

Long-Day Plants

Long-day plants flower when the night length falls below their critical photoperiod (aka, when they receive more than 12 hours of light). Long-day plants include carnations, barley, lettuce, irises and much more.

Short-Day Plants

Short-day plants flower when the night length exceeds their critical photoperiod (aka, when they receive more than 12 hours of darkness). Short-day plants include cannabis, poinsettias, chrysanthemums, soybeans and much more.

How Darkness Influences Flowering

When these names were developed, it was originally thought that the amount of light a plant receives determined when it flowered, thus the terms “short-day” and “long-day.” However, studies have since shown that the amount of darkness a plant receives actually determines when a plant will flower.

This critical importance of long nights is why cannabis plants can have such a detrimental reaction to light during the night cycle of flowering. The light interrupts the night cycle and throws off the plant’s internal clock that tells it how much darkness it has received. As little as 10 seconds of light during the night cycle, can impact the flowering ability of a short-day plant.

Alternatively, to keep a Mother plant in the veg state, just ensure it does not receive more than 12 hours of darkness, as this will trigger a move to flower. This is why Mother plants are typically kept on a similar light schedule to veg plants.

Key Takeaways

Understanding the biology of a plant is critical to successful cultivation and maximized yields. The short-day designation of cannabis is just the beginning of a fascinating biological system that controls everything about the plant. Take the time to see what you can learn and your yields and quality may just increase accordingly.

*** Important note: this information does not apply to autoflowering strains.

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