Marijuana in flower: when does it start and how long does it last indoors?

How long does the flowering marijuana phase last and when does it start?

Modified on: 20/09/2022

Here’s how to know when marijuana flowering starts and how long it lasts

The flowering stage of marijuana is undoubtedly the most interesting and eagerly awaited stage of the whole plant growing process.

Depending on whether the plants come from auto-flowering seeds, feminised seeds, or other genetics, the flowering time can vary, but some key stages signal the start of this phase in indoor growing. 

Let’s find out what they are, talking about both photo-dependent and auto-flowering marijuana plants.

Marijuana and the start of indoor flowering

During the flowering phase (including the timing), the processes may vary due to the cannabis seeds you have decided to sow and the type of cultivation you have adopted, which is mainly divided into indoor and outdoor cultivation.

The start of flowering outdoors coincides with the end of summer, when the days begin to shorten. 

Marijuana in bloom

In indoor cultivation, on the other hand, flowering can be induced using lamps. 


During the vegetative phase (when the plant is developing), the plants are usually given cycles of 18 hours of light and 6 hours of darkness.

When the plant has grown enough, and you want to induce flowering, you have to decrease the light hours (usually to 12) and wait for the plant to give its signals.

In indoor cultivation, the process is induced, while in outdoor cultivation, it is natural, but the trigger for flowering is always the same. 

Basically, when a marijuana plant is subjected to a cycle that includes more hours of darkness, it automatically prepares to flower. After an initial development phase, it stops elongating and starts to devote all its energy and nutrition to produce buds.

Read also: Drying cannabis: 3 things to know

How long is the flowering period?

The length of the flowering phase is usually seven to eight weeks, but there is no fixed rule. Some genetics are very fast, while others take longer to reach full bud maturity (especially some Sativa genetics).

Let’s say that the ideal time to harvest the flowers is usually between the 6th and 8th week.

The first week of flowering can be considered a preparation phase. 

The marijuana plant, sensing a decrease in the number of hours of light, realises that it has to prepare itself for winter and, consequently, bear the weight of the buds that are about to develop. 

So, what happens?

The growth of the plants suddenly accelerates to the point where they sometimes stretch to twice their original size (this phase is also called stretching), and, in general, with the production of new branches and leaves, they tend to become stronger. 

After generating the appropriate structure for flowering, during the second week, the cannabis plant begins to produce the first white pistils: the thin hairs that will shape the buds.

From week 3 to week 5, the plant will focus all its energy on developing the actual buds. As time goes by, the plant’s aromas will become more pungent, the buds will become more formed, and new inflorescences will emerge. 

From about the sixth to the eighth week, the flowers ripen.

Cannabis in bloom

Start of flowering in an indoor auto-flowering plant

We have mentioned in the previous paragraphs that the flowering phase of marijuana also depends very much on the genetics of the marijuana seeds grown.

When dealing with plants grown from auto-flowering seeds or dwarf auto-flowering plants, the point we made earlier about light and dark cycles does not apply.

Auto-flowering cannabis, as the name implies, flowers independently; it is not dependent on the light cycles to which it is subjected. It means that in indoor cultivation, by growing such plants, it is possible to maintain the cycle of 18 hours of light and 6 hours of dark from planting the seeds until the flowers ripen.

Usually, auto-flowering plants enter the flowering phase after about 25-30 days of development and the flowering period lasts approximately one month to 50 days.

In the case of auto-flowering plants, the flowering time is self-contained and is much faster than in other cannabis genetics.

Read also: How to get huge cannabis buds in 5 easy steps

To conclude

As we have seen, the flowering period of marijuana lasts about six to eight months for most cannabis genetics and only a month or so when dealing with auto-flowering plants.

In addition, when growing photo-dependent cannabis plants, the flowering phase must be induced in indoor cultivation by increasing the hours of darkness. Whereas when growing auto-flowering marijuana, the process will begin independently after about a month and will be recognisable by the sudden growth of the plant and the production of white pistils.

We hope you enjoy reading this article and invite you to visit our online shop, SensorySeeds, specializing in selling cannabis seeds online.

Please note, however, that growing cannabis is not permitted in most countries, but you can buy seeds for collecting purposes:

feminized seeds, auto flower seeds, fast growing weed seeds, there is something for every taste! 

We look forward to seeing you on!