Medically Reviewed by
Jason Crawford

Article Last Updated on January 14, 2023

Knowing all the phases in the lifecycle of the marijuana plant is key to understanding its needs and getting the best harvest you can possibly get. The three most important stages are the germination stage – when the seeds are preparing for new growth, the vegetative stage – when the plant grows and is getting stronger, and the most important of them all: the flowering stage – when your crops finally start the process of bud formation.

The flowering stage can also be more demanding than the vegetative stage, for example, therefore, knowing what to expect is an essential part of the process. The end result is very rewarding, so keep reading for some in-depth details about how long the flowering period lasts and what you can do to get the best results.

When Does the Cannabis Flowering Stage Begin?

During the vegetative stage, the energy of the plant is mostly focused on getting the needed nutrients, growing stronger and sturdy roots, and developing its fan leaves. Once this stage ends, it slowly starts preparing for the next one.

As a rule of thumb, in nature, the flowering stage begins when the veg stage has ended, which is towards the end of the summer and beginning of fall. This time of year the amount of light that the marijuana plants get starts getting smaller and the temperatures start dropping, signaling that it’s time for flowering. Therefore, less light and more darkness in nature lead to the start of the next stage.

For indoor growers, the light cycle is different. If you grow cannabis inside, you’ll need to adjust the photoperiod to 12 hours of light and 12 hours of darkness to trick the plant into thinking that fall is near and that it’s time for flowering.

For auto-flowering strains, the light schedule is unimportant as the genetics of the plant dictate the start of the flowering phase.

How Long Does It Last?

Depending on the strain, the flowering cycle lasts anywhere between 7 to 9 weeks, and for some cannabis strains, like certain Sativa strains, it could take longer as they need extra time to mature.

During these weeks, the plant goes through several growth stages and needs more care and attentiveness. If anything goes wrong, it might affect the quality of your buds, unlike the vegetative stage, when you can reverse nearly any type of damage.

Weeks of the Flowering Stage

Let’s break down the flowering stage into the distinct phases that your crops go through when they flower.

Weeks 1-3 – Transition Phase

During the first few weeks, the plant starts slowly transitioning towards flowering. During this stage, the crops are still resilient and you can fix any problems that may arise, like infestations or nutrient deficiencies.

Your crops will start to experience some dramatic changes as they will gradually start stretching and growing in size – some may even grow twice or three times their height. This is needed so that your plant can handle the sprouting of the buds.

Some growers continue providing their cannabis plants with nitrogen, phosphorus, and potassium during this phase, while others believe that an excessive amount of nutrients will stunt the stretching and hinder the plant’s growth. It’s best to do your own individual research on this and decide based on the needs of your crops.

You’ll notice that the female cannabis plants are slowly starting to develop the pistils, which are the thin white hairs located at the top of the clusters of single leaves that have formed on the branches. These white pistils will soon develop into budlets. The male plant, on the other hand, won’t develop pistils, but pollen sacs, and this is how you’ll differentiate between the two.

Weeks 3-4 – Forming of Budlets

After the third week, the crops will slow down with the stretching process and they’ll start forming little buds. During this phase onwards the plants will be quite sensitive, so you’ll need to be extra attentive and careful as any wrong step will result in an unsuccessful harvest.

Make sure to often inspect and closely observe your plants to detect any signs of nutrient burn – you’ll notice this if the tips of the leaves are yellowing or turning brown. If this is the case, reduce the amounts of nutrients immediately or the damage will spread to the rest of your crops and impair photosynthesis. Nutrient deficiencies, on the other hand, are not as detrimental as you can always add more if you need to.

If you notice a few yellow leaves at the bottom, don’t worry, it’s normal and you can trim them. It just means that the energy of the plant is now directed towards the bud sites and some parts may suffer.

The best part of this phase is that you’ll start noticing an odor coming from your weed garden, meaning that your flowering plants have started developing their terpenes and flavonols.

Weeks 4-6 – Budlets Begin to Fatten

In this phase of the flowering stage, the stretching is minimal and the focus of the plant shifts entirely towards fattening the budlets. At this point, the fan leaves should be a vibrant green color and the pistils should begin to darken.

During these three weeks, it’s recommended that you lower the humidity levels to 40-50% to prevent bud rot and slightly lower the temperature of your growing room. Move your grow lights further away and adjust the lighting to prevent light burn.

You may still see some bottom fan leaves turning yellow, and as long as there are only a few of them, there’s no cause for concern.

Weeks 6-8 – Maturation of the Buds

By now any remaining vegetative growth stretching will have stopped and the buds will continue thriving. You’ll notice that the buds have gotten the biggest they’ve been, you’ll see they’ve developed some sticky resin on their trichomes (the source of cannabinoids), and the odor will definitely become more noticeable.

To not hinder their growth, it would be wise to stop adding nutrients to prevent nutrient accumulation that will negatively impact the flowers. It’s also recommended that you lower the humidity again, to 30-35%, and increase the temperature difference between day and night. If needed, increase the airflow of the grow room to prevent overheating and excess moisture.

Weeks 8+ – Final Stage of Flowering, Flushing, and Harvest Time

So, now you know all that, but you’re still wondering when to harvest cannabis? Well, this will be ready to harvest depends on the type of strain you’re growing, not whether you use hydro or soil. There are some tell-tale signs that can help you discover when it’s time for harvest.

First, for most weed strains, the pistils should change color, from white to orange, meaning that the production of new buds has come to an end. The trichomes will also change colors as the THC content increases, turning from clear to milky, and the aroma will be very pungent.

You should know that once you start seeing these changes, you’ll have one week to harvest and collect the flowers before THC starts degrading into CBN. If you notice the trichomes turning amber color then this process has already started.

One last step before harvesting is flushing your crops. Flushing means running clear water into your growing medium in order to force the plants to take up any unabsorbed nutrients. This is supposed to improve the aroma and flavor of the buds as excess nutrients will produce a more chemical and harsh flavor. The amount of water you need is three times the volume of the growing container. Just add the water and let the excess drain from the bottom.

Bottom Line

The flowering stage is the most important stage for the cannabis growing cycle, and it’s also the most important process for growers in achieving a successful harvest. During this stage, the plant goes through many phases in preparation for flowering and all the while developing its characteristic chemical profile.

It’s recommended for growers to be as attentive as they can during this stage of the marijuana plant’s life cycle because it’s the only way to get THC-laden fragrant buds.

A passionate advocate for the benefits of cannabis. Fraser Horton, who has a background in botany and a strong love of nature, has spent years researching how cannabis affects the body and mind. He established Leaf Nation in 2020, where he has devoted himself to educating people about the legalisation of marijuana and its safe and responsible use. Fraser is committed to highlighting cannabis’ potential for improving wellness and working to dispel the stigma associated with its use.


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