The Life Cycle of a Cannabis Plant from Seed to Harvest

Cannabis: An Annual Plant

Cannabis is an annual cultivar which means it flowers once a year and then dies. Like many plants, weed cannot withstand the intense conditions of the winter and will try to reproduce before the time comes. Indoor growing techniques have allowed growers to have better control over the cultivation cycles, and now we can grow all year round in all kinds of climates.

After the countless crossing of genetics, breeders have managed to adapt cannabis to suit their needs while still allowing the plant to live its life to its full potential. The inevitable result of human intervention has lead us to create an array of breeds with short flowering cycles and stable genetics, such as those found in feminized seeds or autoflowers.

With all the variables that come with growing different strains, it can be confusing knowing exactly what will happen during each phase. Beginner growers will benefit most from seeing the magic happen with their own eyes. The best way to learn about the life cycle of a cannabis plant is through experience. This guide will give you a simple starting point so you know what to expect once you have germinated your first seed.

Feminized Seeds

Today cannabis is super resilient and even more productive. Along with the rising levels of THC, there are now hundreds of cultivars, all with their own unique traits. Feminized seeds are bred to have specific characteristics like high yields or resistance against mould. 

Having male cannabis plants is only really useful for a grower who is interested in breeding, so stick with the females if you only want bud. Growers often choose feminized seeds because they have an almost 100% chance of being female.

Feminized seeds have dominated the market over the years because of their reliability and genetic stability. They are highly recommended for saving time and resources as well as to remove the risk of males appearing in your garden. 

There is still a small chance that female plants try to develop male flowers but it is very unlikely unless they become stressed. A female plant that show signs of male genetics is what is known as hermaphrodite. Otherwise known as a 'hermie', a hermaphrodite plant will produce both male and female flowers as it tries to reproduce. It is a rare occurrence but should not be overlooked. 

Diary End (Male Plant)

Note: The signs of a hermaphrodite can be determined by 'bananas' growing from bud sites. As the name suggests, they look like tiny yellow bananas and are quite obvious when they do appear. Hermaphrodites should be removed from a garden immediately if you are not looking to breed your plants.

Hermaphrodites can show both male and female preflowers.

Autoflowers

Autoflowering plants descend from the Ruderalis family. This genetic history means they flower automatically and do not depend on a photoperiodic change. 

Because autoflowers do not rely on a light schedule, they can be grown under 18 or 24 hours of light for their whole cycle and will still flower.

The first signs of flowering can arrive just 2 weeks after germination. By 4 weeks an autoflower will be in full budding mode. Most strains will be ready in under 10 weeks, from seed to harvest. Some take a bit longer but either way they are faster than feminized seeds. 

Autoflowering seeds do not yield as much as feminized seeds do, but are ideal if you are looking for quick grow cycles with relatively small plants.

Mother Plants

Female cannabis plants can be kept in their vegetation stage as long as they are under 18 hours of light. Having full control over when you flip your light schedule gives you the possibility to keep a mother for cloning.

Mothers are stable female cannabis plants that never flower. A healthy mother gives you the possibility to make hundreds of copies of a certain genetic. This means picking the best, fastest growing and most robust plant from a garden so you know all future plants will be just as vigorous.

Having a mother plant is useful for commercial growers as it saves loads of time in the beginning stages of the growing process. Cutting a clone will cause the shoot to produce hormones that stimulate root growth. Hormonal supplements are often used to aid the process and make the probability of rooting much higher.

Germination (1 week)

Germinating happens at the very beginning of a cannabis plant's life. It is the activating of the hormones in the seed by adding water. A seed is very delicate but also holds all the necessary information in it to grow into a magnificent cannabis plant.

As soon as a seed recognizes it has moisture surrounding it, the cells in the seed germinate and begin forming a tap root. Once this white root shows, a seed has germinated and is now considered a sprout.

Gravity is an important factor in this process as it signals which way the root needs to grow. After rooting, a sprout will push its head up and out into the world to find light. This happens after about 3-7 days and is the beginning of the next phase of growing as the plant turns into a young seedling.

Sprouts need very stable conditions if they are going to thrive. The average temperature levels they do best in are between 20-25°C, with a humidity level of around 60-80%. They will require watering but only small amounts to keep the growing medium moist enough to encourage root growth. Because there are basically no roots yet, the absorption of water is minimal meaning watering too much can drown them easily.

A successful germination process is key to achieve healthy grows with big yields. A plant that does not have a smooth start will often end up being slow, under-productive or more susceptible to problems like fungus or rot. Some seeds just don't germinate either because they're either too old, dud (dead), or just couldn't absorb enough water to weaken the outer shell enough.

Seedlings (1 - 2 weeks)

Two tiny leaves will open up from the top of the sprout as it emerges from the growing medium. These are called cotyledons and they provide the necessary energy for first stages of growth as photosynthesis begins.

A few days after this, the first 'real' leaves start to grow from the centre. The cotyledons will turn yellow and fall off eventually when the plant has matured into its vegetative state.

The next 10 days or so have relatively slow foliage growth (in comparison to later stages) as the plant focuses on developing a solid root structure. Creating a stable, healthy foundation for itself allows the plant to have enough support for massive growth later on. The root system is also responsible for the absorption of vital nutrients.

Leaves will start growing opposite each other along the main stem, alternating at the internodes. The first sets of leaves only have 1 finger, not like the later leaves which have up to 7. Once there are 3 or 4 leaf internodes with leaves that have at least 5 fingers, they have grown out of their seedling stage.

Tip: Seedlings enjoy high humidity and warm temperatures. Keeping a consistent environment for them helps them to progress much faster, so a propagator is recommended. The vent holes can be opened slowly each day so they steadily become accustomed to the change of environment.

Vegetation (4 - 8 weeks)

After 2 weeks cannabis plants will be in their vegetation phase. During this part of the cycle there is a lot of development happening in both the root zone and the main structure of the plant. There will be a surge in the branching activity and small shoots can be noticed emerging from the leaf nodes.

The time of vegetation depends on whether it is being grown indoors or outdoors. If a seedling has been transplanted outside, the length vegging cycle will vary based on when it is planted and in which region. Vegetation will end eventually once the daylight hours reduce towards the end of summer. 

Indoors, growers have full control over the light cycle. By maintaining a light schedule of 18 hours, cannabis plants can be kept in their vegetative state, meaning they can be grown for as long as needed until you put them outside or switch to a photoperiod of 12/12.

By the 4th week of vegging a cannabis plant should be matured with lots of sets of branches and fan leaves. This is the time growers can begin to apply training techniques such as defoliation, topping or LST/HST. Plants will need their full energy by the time flowering begins, so training should take place with enough time for recovery.

Blueberry X Afghani (Shiskaberry)

Most of the available nutrients in the growing medium have been used by this point, so cultivators will normally start adding them. Without the essential minerals a cannabis plant can become deficient and produce low yields. Signs of deficiency are shown through various changes in colour or shape of the leaves. 

Flowering (6 - 16 weeks)

The flowering stage is always an exciting time for a cultivator. It is more of a gradual process when growing outdoors but indoors the sudden decrease in light forces plants to flower, resulting in a period of explosive growth. After flipping a light schedule to 12/12, plants can often double or triple in size in a matter of 2-3 weeks.

This is the moment where a cannabis plant will show signs of its sex. Preflowers will start to appear around the internodes of the branches and the main stem. Female cannabis plants will develop small calyxes with white pistil hairs, while male flowers look like small, green pollen sacs.

Male preflowers (left) look like small pollen balls, whereas female preflowers (right) have a calyx and pistil hair)

If a plant is male then it will not produce bud (the flowers). Males will try to pollinate females if they are not removed from a garden and in most cases are a problem because the final product will have seeds in it. 

After the first couple of weeks of flowering, female plants start to grow huge quantities of calyxes around the node areas. The production of resin begins as trichomes form around bud sites, covering the calyxes and other leaf areas. If a plant has the right conditions it will keep producing until it reaches full sexual maturity.

Indoors, flowering will happen in a set amount of time based on the strain's genetics. Indicas flower in as low as 6 or 7 weeks whereas sativa dominant strains can take up to 16 weeks or longer. Outdoors, the maturity time of a cannabis plant is still genetically determined but less accurate.

A plant reaches the end of this cycle after the trichomes start turning cloudy or amber. Calyxes will usually fatten out and the scent will be at its fullest. This is around when THC levels are at their highest. You can also see this change through the pistil hairs, as they start to brown and curl inwards. Again, this can be different for some strains, which can still have plenty of white pistil hairs and be ripe for harvest. 

Tip: Preflowers can show in some genetics before the flowering phase. Even feminized seeds have a chance of turning hermaphrodite so if you want to avoid producing seeds, start checking early on.

Harvest

The day will come where you will need to harvest. The end of the harvesting window is the final phase of a cannabis plant's life as it begins to degrade and eventually die. Organic matter starts to break down, increasing chances of mold. 

For outdoor this will be by the time autumn ends in October/November (northern hemisphere), but it all depends on the region and local climate. Harvesting should take place before temperatures drop too much to avoid a crop being ruined.

Harvesting requires you to cut down your plants, manicure them and hang them up upside down for drying. Manicuring, or trimming involves removing most of the leaves while the plant is still wet, which better preserves the trichomes. If you manicure when a plant is dry, trichomes fall of easily resulting in a loss of flavour and potency.

Growers have experimented with harvesting at different stages and there has been many discussions about how cutting early or late affects the high and flavour. After THC content reaches its peak, potency begins to drop as CBN levels rise. Higher CBN content weed tastes harsher and has a much more sedative effect, making it useful for medical applications such as treating pain. 

Royal Gorilla by KrautFabrik from GrowDiaries ready for harvest.

Tip: It is recommended to wash out any remaining nutrients by flushing for 2-3 weeks prior to harvest.

Indoor Vs Outdoor

The life cycle of a cannabis plant varies hugely when growing indoors or outdoors, and each comes with its own set of benefits. Through years of selective breeding, grow cycles have been steadily getting shorter as industrial demand increases. 

Benefits of growing indoors:

• Short grow cycles - growers can get multiple harvests per year.
• Plants can be grown as big as you want before flowering - you decide what cycle is best.
• More control over the conditions - no risk of strong winds or intense storms.

Growing outdoors will mean you are at the mercy of Mother Nature although there are still plenty of advantages that make it a better choice for some.

Naturally, the flowering phase will happen gradually as light decreases over the summer period. Transplanting should take place while there is still enough weeks of long light before the summer. Remember, the rule of thumb is that cannabis plants grow under 18 hours of light and flower under 12.

Benefits of growing outdoors:

• Bigger yields - outdoor plants can grow huge like trees.
• Cheaper - most of your energy costs are covered by nature.
• Less maintenance - no more having to deal with electrics, pumps and timers.

Choosing indoor or outdoor growing relies on you and your needs as well. Cannabis is a very versatile plant and is a breeze once you find the method that works for you. How you grow and what you grow depends on factors like your weekly schedule. If you are planning a long vacation in the middle of summer it might not be the best idea to be starting your outdoor season. Make sure you are there to monitor your plants so you know they are on the right track. 

Knowing how seasons change in your region can help you determine when the best time to germinate/harvest is.

Conclusion

There is tonnes of information out there regarding the life cycle of a cannabis plant and it can be a bit overwhelming when you are just starting out. The best way to learn is by experimenting through trial and error. Making mistakes is part of the cultivation process and will only make you a better grower.

This article should provide you with enough knowledge to understand what different stages you should be focusing on throughout a cannabis plant's life, and hopefully save you some hassle along the way. Being able to recognise what is happening in your garden will become a second nature to you and you'll soon be a master grower.

External References

Seed Germination Behaviour of Cannabis Sativa L. Under Different Temperature Regimes. - Kumar, Birendra & Zaidi, S & Singh, Vagmi & Venkatesh, K & Ram, Georgia & Gupta, Anil & Kumar, Narendra & Samad, A. (2020)

Night Interruption Lighting Equally Effective As Daylength Extension In Retaining The Vegetative State Of Cannabis Mother Plants. Crop, Forage & Turfgrass Management. - Whipker, Brian & Cockson, Paul & Smith, James. (2019) 

Overview Of The Cannabis Industry. - Knutson, Kathy. (2020)

This article was updated January 2021.