How lighting induces flowering for indoor marijuana

The process of growth for a marijuana plant is the same as it is for all the other different plants and light is one of the biggest players. Light enables photosynthesis in all plants and the same applies to weed, a process that allows the production of food and energy.

The good news is that, with an indoor setup, you the grower can very much be able to manipulate when the plant flowers. The marijuana light cycle is the easiest to control especially when the plant is grown indoors giving the grower control on when to harvest. Naturally, the cannabis plat begins flowering during the summer and in the early fall.

This way, the female marijuana plant is able to attract pollen and produce seeds in an outdoor setting. With longer nights and shorter days, photoperiodism is triggered for the plant to stop vegetating and allow flowering.

There are color pigments in the leaf called Phytochrome Red (PR) and Phytochrome Far Red (PFR). Whereas PR absorbs red light between 660 and 760 nm, PFR absorbs far red light between 760 and 800 nm. It is these two pigments that chemically react to the light, and trigger the plant to either flower or not. In an indoor setting however, this process can, be manipulated depending on the growers needs.

Keeping it vegetative

The more light that is supplied to the plant, the less the darkness and hence the plant is kept in a vegetative stage. As a result, the cannabis plant will grant you more leaves like the plant was experiencing an extended summer.

flowering indoor marijuana

flowering indoor marijuana

How to Induce Flowering

The reverse is also true for growers in need of the plant to flower. PFR is produced by plants when exposed to more light which contains far red wavelengths. With no light, PFR is turned into PR. Although this does not affect the plant in any way, the plant gets affected when the hours of darkness are prolonged inducing a significant drop in PFR.

When you need your cannabis to flower, all you have to do is change up the light cycle to enable just that. In this case, the hours of darkness are more than the hours of light. Therefore, you should never ever enter your grow room when the lights are turned off.

How to ensure no light in the grow room

With the lights out, enter the grow room and wait for 15 minutes when your eyes have fully adjusted to the darkness to ensure that there are no light leaks.

Ensure that there is no light coming through from under the door, through a curtain or even through the ventilators.

If any of the equipment produces light from the display, you might have to cover it up with duct tape.

Make sure that you completely see nothing while in the grow room.

Note: Pure sativa strains are not as sensitive to light changes because they originate from the tropical regions given the fact that day and night are more stable there. This explains why sativa strains stay in the vegetative stage for a much longer time as compared to other strains.


With indoor growing, you no longer have to really on the natural factors or even have to wait for longer periods before your marijuana can flower. It is just a play between time and light. The more the light the more leaves you get while the more the darkness the sooner it is for you to harvest.