How Cannabis Plants Grow, The Full Life Cycle

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Before you can grow cannabis, it is a good idea for you to understand how cannabis plants grow. Cannabis is an “annual plant”, which means it completes its growth cycle within a year. Cannabis plants like Indica and Sativa will grow depending on what season it is. They do this by detecting how many hours of light it gets per day[1]. If the days are long, such as spring time and early summer, the plant will be in vegetative growth. They bloom during the summer time, when the days become shorter. Their life cycle ends before winter sets in. 

When grown outdoors, cannabis plants will grow according to how much light they get per day. The same principle applies indoors. By controlling how long the day is in your grow room, you will control which stage of growth your plant is at. So to make it easy to follow, we will cover the natural life cycle of a cannabis plant outdoors. From germination in spring, to harvest time in autumn. Growing indoors will be the same, but you will control how much light the plants get. 

How a Cannabis Plants Life Cycle Begins

Like most plants, it all begins with a seed. Spring time comes, and the temperature starts to rise. When the conditions are right, cannabis seeds leftover from last year’s plants will germinate. A little root pushes its way out of the seed in search of water and nutrients.  As the root grows into the ground, a shoot will grow upwards. 

Within a couple of days of the root growing from the seed, there will be a small shoot growing above the ground. This is known as a cannabis seedling. 

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The Seedling Stage

When a cannabis seedling first emerges from the ground, it will have two small round leaves on a stem. These leaves are called cotyledons. They will push their way upwards searching for light, and the roots will push downwards searching for food and water.  

The spring days are long, and the seedling will receive over 16 hours of light per day. It will continue to grow taller, with more leaves. The main tap root will push its way further down and more roots will branch out from it. 

After 2-3 weeks, the plant will have a few sets of leaves, with a good root base to anchor it in place. It can get enough water and minerals from the ground, and plenty of light from the sky. It is ready to move into the next phase of growth, vegetation. 

Cannabis Plant Vegetation

During the vegetaive stage of growth, a cannabis plant will focus mainly on making more leaves, branches, stems and roots. It wants to grow as big as possible to make sure it can hold plenty of flowers later in the year. 

Every day a “vegging” cannabis plant will get over 16 hours of light. It uses this light for photosynthesis to make more and more food. The more leaves it has, the more light it can catch. The more light it catches, the more food it can make. 

Through the months of spring and early summer, the plant will grow in the veg phase. It can grow anything from a few feet tall, to a few metres. As the summer months pass, and the days start to get shorter, the plant will receive less light per day. Eventually, it will receive less than 14 hours of light. This tells the plant that summer is coming to an end, and it is time to make flowers. 

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Early Flowering and Signs of Sex

When a cannabis plant flowers, it will begin to grow its reproductive parts. A cannabis plant can be male or female[2]. Male cannabis plants will grow flowers that produce pollen. This pollen is released into the air and lands onto the flowers of female cannabis plants. If this happens, the female will produce seeds in her buds. 

Because most cannabis users prefer cannabis buds without seed (sensimilla), male plants are often cut down and discarded to prevent them pollinating females. So it is important to be able to identify if a plant is male or female early into the flowering stage. 

Male Cannabis flowers

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Male cannabis plant flowers will look like a small ball, on the end of a stalk. As the flowers grow bigger, they begin to resemble a bunch of grapes. The pollen from a male plant isn’t active until 10-14 days after the flowers have started to form. 

When the pollen sacs are ready they open and release pollen into the wind[3]. If it lands on the flowers of a female cannabis plant, the female will grow seeds. To prevent this, male plants are identified early, and removed from the grow room.

Female Cannabis Flowers

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Female cannabis flowers are also known as buds. This is where the THC, CBD and other cannabinoids come from. To begin with, pre-female flowers will grow similar to male pre-flowers, but they will be tear shaped rather than round and they will have whites hairs (pistils) coming out of them. 

The pistols are there to catch pollen from males. When pollen lands on one, it will dry out, and a seed will grow in the calyx. The more pollen that lands on a plant, the more seeds it will grow. 

The Flowering Stage

The length of the flowering cycle will differ depending on types of cannabis. Sativa cannabis plants will flower for up 20 weeks, whilst indica cannabis plants will flower in 8[4]. During this time, the buds on a female plant will grow bigger and bigger, whilst producing cannabinoids and terpenes. Male plants will continue to grow flowers and produce pollen. 

If a female has been pollinated, the buds will fill with seeds. If not, she can focus more energy on making more cannabinoids. At some point, a cannabis plant will reach peak production. During autumn the night becomes long, and the temperatures fall. This is when cannabis plants will be harvested. 

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The End of a Cannabis Plants Life Cycle

A cannabis plant can not survive the cold of winter, and as it approaches, the plant begins to die. The seeds she has in her buds will take half of her genetic code, and half of the males onto the next generation. When spring comes, the seeds will germinate, and the process begins again. 

How Auto flowering Cannabis Plants are Different

Autoflowering cannabis plants work a little differently. Instead of flowering according to how much light they get every day, they flower when they are mature. Usually this is a round 4-5 weeks after germination. 

The average lifespan of an auto flowering cannabis plant is around 12 weeks. This means the plant will be ready for harvest around 12 weeks after the seedling rises above the ground. The vegetation period of autos will be between 4 and 5 weeks. The flowering period will differ depending how sativa or indica dominate the plant is. 

Autos can be grown throughout spring, and summer outdoors, no matter how long the days are. Most indoor cannabis growers will grow autos on at least 18 hours of light per day with 6 hours darkness for their whole life cycle. 

FAQ about How Cannabis Plants Grow

Is growing cannabis indoors better than growing outdoors?

If the time of year is right, and you have enough space to grow outdoors, then that is the best option. But this isn’t viable for many people. Growing indoors offers its own benefits. Like being able to control the environment, you can grow all year round, and you can keep bugs away easier. It really depends on your own personal circumstances. 

How long does a cannabis plant take to grow?

In its natural environment a photoperiod cannabis plant will grow for around 8-9 months. They will start growing in early spring, and be harvested in late autumn. Indoors, photoperiod cannabis plants can be kept in veg for years. But most growers will give around 6 weeks of veg, and then flower the plants. The length of the flowering period will depend on whether the plant is Indica or sativa dominant. Autos will grow for around 90 days before they are ready for harvest. But again their flowering period will depend on how Indica or sativa dominant the plant is. 

Should I grow Autos or Photos?

Why not both? Photoperiod plants will get a huge yield when they have been vegged for a good amount of time. Especially if they are grown outdoors. But autos will grow quickly, and bring top quality buds too. Take a look at some of the grow diaries in our cannabis growers forum. You will have to be signed in to see them. But there are plenty there for you to read so you can decide what’s best for you.

What’s next? 

Now we understand how a cannabis plant grows during each stage of its life cycle. But we mentioned how photoperiod plants will only flower under 12 hours of light and 12 hours of darkness. So the next step will be to fully explain the light cycles used for cannabis plants. So you know how much light to give to your plant, for each stage of growth and why. 


1)Cannabis sativa L. – Encyclopaedia of Life Archived 28 August 2009 at the Wayback Machine. Retrieved on 7 August 2011
2)Ainsworth, C (2000). “Boys and Girls Come Out to Play: The Molecular Biology of Dioecious Plants”Annals of Botany86 (2): 211–221. doi:10.1006/anbo.2000.1201.
3)Clarke, Robert C. 1991. Marijuana Botany, 2nd ed. Ron Publishing, California. ISBN0-914171-78-X
4)”The Difference Between Indica and Sativa”. Max’s Indoor Grow Shop. 2019-12-12. Retrieved 2020-05-08.

8 thoughts on “How Cannabis Plants Grow, The Full Life Cycle”

  1. Posted by: @woodi2

    Where will it be located, in the regular grow forum?

    On the front end of the site in the main guides, and in the basics fo growing section of the forum 🙂

    Posted by: @stootie

    When you get all the grow guides finished it would be cool if it could be turned into a little Percys grow guide book

    I am hoping that will be the case when it is done 🙂 A long way to go though 

    Thanks for all the kind words lads, glad you all approve 🙂 

  2. @macky Good job on this again mate, When you get all the grow guides finished it would be cool if it could be turned into a little Percys grow guide book that we could buy, A4 or a small notebook, be handy to have if the internet ever stops working, just a thought :d  

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