The cyclical rotation of the cannabis light cycle is very important. The first question to ask is what kind of plant am I growing?

This is because there are two different kinds of marijuana plants: photodependent and autoflowering.

Photoperiod cannabis strains need a decrease in light hours for flowering to occur, while autoflowering strains with any type of light/dark schedule, after 25-30 days will go into flowering automatically. In this regard, the first decision to make is whether to grow photodependent or autoflowering plants

These expedients will greatly influence the planning of an indoor cultivation, not least the cost of the energy used.

Below we will explain how to set the cannabis light cycle in indoor growing with both species.

Autoflower light cycle: how many hours of light for indoor growing?

Growing autoflowers indoors does not require a change of light hours between the growth and flowering phases, which means that they flower regardless of the light hours provided. Whether we set 18, 20 or 24 hours of light, autoflowering plants will flower after 25 to 30 days. In our experience, 18 hours of light for autoflowering plants is perfectly fine to ensure healthy development and abundant flowering of the plant.

However some growers claim that with 20 hours the plant develops faster, also giving more abundant flowering. Much also depends on the pot supplied to the plants which must not be less than 11 liters in volume.

To learn more about the techniques for growing autoflowering plants, we recommend reading our guide on growing autoflowering marijuana.

Schedule light hours for photoperiodic plants cycle

Photodependent cannabis plants need, in the initial phase and throughout the growth period, 18 hours of light a day and 6 hours of darkness, recreating the luminous conditions of summer with long and luminous days. In this phase, MH or Agro lamps can be used.

When to switch to the flowering stage?

Once the growth period is over, which usually lasts between 25/35 days if you want to induce the plant to flower, you will have to switch to a photoperiod of 12 hours of light and 12 of darkness, recreating autumnal conditions. The decrease in the hours of light in cannabis growing will cause the plant to show flowering, about 10 days after the time shift.

In these first ten days you will notice a sudden lengthening of the plant which will stop with the formation of the flower. In the flowering period HPS or Agro plant lamps can be used.

The main advantage of growing photoperiod cannabis indoors is that artificial light allows us to control and plan the flowering stage. We would therefore have the possibility to define the maximum reachable heights, choosing the best moment to go into flowering, simply by decreasing the timer from 18 to 12 hours of light.

Feminized seeds indoors how much light?

The same concept of autoflowering plants does not apply to the light hours of indoor feminized plants, therefore it is necessary to decrease the photoperiod to induce flowering.

Plant light cycle for outdoor growing

In outdoor growing, not having control over the photoperiod and the hours of light in the flowering phase , we are totally dependent on the natural plant cycle which vary with the passing of the seasons. As many of you know, daylight hours increase day by day after the winter solstice. the days lengthen until the summer solstice in June. From that moment on the days start to get shorter again.

Those who grow light-dependent plants outdoors are familiar with these cycles. So we recommend sowing cannabis in early spring, when mild temperatures are already sufficient for germination and growing hours. Usually plants tend to start the flowering phase towards the end of summer, or when they perceive that the days are starting to get shorter and the nights to get longer.

Instead, if we grow autoflowering plants outdoors, we can start planting in spring and if the latitudes and climate allow it, we can even complete 3 cycles. This is because, as already mentioned above, this variety of cannabis does not require a decrease in the hours of light for flowering . It is clear and understood that the best results in terms of yield with autoflowering cannabis will occur in the months between mid-May and mid-August, where the hours of light will be at their maximum length. If you want to learn more about techniques and advice on growing cannabis, consult our guide.

Hours of light indoor cannabis cultivation how to keep the photoperiod stable

To avoid sudden changes in the photoperiod, it is absolutely necessary to use an analog timer that marks the hours of light in indoor growing. An irregular switching on of the lighting system could cause serious problems for the plants such as: hermaphroditism, slowdown of development and in some cases even death itself.
Many novice growers often make the mistake of manually turning the lamps on and off, we strongly advise against this practice if you don't want to have serious problems in plant growth.

if interested, consult our guide to learn about the light spectrums useful for indoor cultivation: Par, Ppf, Lux and Lumen: Guide to the light spectrum useful for plants