marijuana plants flowering stage

Get the most out of your cannabis seeds and plants with a thriving flowering stage indoors!

After germinating your cannabis seeds and coaxing your seedlings through the vegetative stage, your plants will enter the flowering stage.

During this period of growth, the little white “pistils” that popped up near the end of the previous stage will begin to change and buds (or “flowers”) will start to develop at the nodes of the plant. These flowers, along with the resinous leaves fanning out around them, are the components that offer so many amazing medical benefits to patients.

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cannabis seeds flowering stage cultivation

Watch for the Flowering Stage signs!

How Long is the Flowering Stage?

Just like the vegetative stage, the flowering stage can vary depending on the strain of cannabis. Two to three months is the average length of the flowering stage, but some strains can be ready for harvest in as little as one month, while others take up to four.

Though the type of cannabis ultimately dictates plant size, two visual cues can indicate it is time for the flowering stage to begin:

  • a plant height of 20”,
  • and the development of some little white hairs growing near the intersect of the stem and the branches.

Read More: Harvesting your cannabis plants

Flowering Stage Light Schedule

Did You Know?:

The flowering stage is activated by altering the light exposure the cannabis plant receives (with the exception of auto-flowering varieties).  During the previous vegetative stage, the plant should have received between 18 and 24 hours of sunlight or high-intensity artificial light each day.  To begin the flowering stage, illumination is changed to a 1:1 ratio: 12 hours light to 12 hours dark.

light schedule during flowering stage

Some cannabis growers make this switch instantly, while others give the plants a few days to adjust, extending the initial six hours of darkness to eight, then 10, and finally 12.  Regardless of the method you choose, the dark periods of the flowering stage must be absolute.  If any work needs to be done during that time, green wavelength bulbs can be used, but any other light will confuse and stress the plants, potentially ruining the crop.

Most cannabis growers recommend keeping the “dawn” time the same throughout this change in light.  In other words, if the 18 hours of light began at 6 am during the vegetative stage, the 12 hours of light should still begin at 6 am during the flowering stage.

The distance between lamp and plant should have been closely monitored since germination, and it is important this attention continues into the flowering stage.  The lamps should remain two feet above the plant tops at all times to avoid overheating or burning the cannabis. For more information, see Building a Grow Room.

Flowering Stage Nutrients

nutrients marijuana flowering stage

Your cannabis plants need different amounts of nutrients during the flowering stage.


Nutrient provision should also be altered during the flowering stage, to ensure the plants are getting enough of the nutrients they need, and not too much of those they no longer require.

Nutrients Before the Flowering Stage

During the vegetative stage, the fertilizer will be made up primarily of nitrogen, phosphorous, and potassium (N-P-K).  At the onset of the flowering stage, the nitrogen will be minimized, and the potassium and phosphorous maximized.  “PK” fertilizers, also known as “bloom fertilizers”, ensure the cannabis is getting what it needs to make the most of this new phase.

Less N, More P and K

Turns out the difference between N and P is alot more than O!

Though during the flowering stage most of the cannabis plant’s energy will be focused on preparation for, and development of buds, growth still occurs – and quickly – in the first two weeks.  Some growers continue administering the grow fertilizer – that N-P-K mix – up to the third week of the flowering stage, while others switch to a PK mix as soon as the lights change.  If the latter method is used, less growth will be seen in this stage, but there should not be any detrimental effects.  In fact, switching to a PK mix immediately upon entering the flowering stage can be a useful step if space is becoming tight in the grow room.

As always, remain mindful of how much fertilizer is used. Stick to the recommendations on the bag or bottle.  If the cannabis plants seem to be suffering during the flowering stage, always eliminate other possibilities before increasing nutrients.  This is particularly important as you near harvest; too much fertilizer can create an unfortunate taste in the dried buds.

The Importance of Air Quality in the Grow Room

marijuana-plants-oxygen-carbondioxide

The takeaway, here:

The more CO2 available to the plants, the faster they will grow, and the more tolerance they will have to the heat in the room!

In addition to CO2, general air flow must be considered (or reconsidered) during the flowering stage.  Now that the cannabis plants are full and bushy, they are likely quite close together in the room.  It is essential that air be able to move through the plants – air infused with both CO2 and oxygen. This can be assured using fans, which circulate the air and imitate the breezes of a natural, outdoor environment.

When positioned around the room, but never pointed directly at the cannabis plants, fans can also be helpful in diminishing humidity.  During the vegetative stage, the humidity in the grow room should be between 60% and 70%.  During the flowering stage, it should be lowered to around 40%.  This can be done incrementally, with the percentage decreasing slightly each week, or done quickly at the start of the flowering stage, with a dehumidifier.  The latter method is recommended by some growers as a way to gently stress the cannabis, which encourages better resin production on the buds.

Flowering Stage Phases

flowering stage phases cannabis

During the Flowering Stage, your cannabis plants go through four sub-phases.

The Four Sub-Phases of the Flowering Stage:

  • As previously mentioned, the flowering stage can begin when one or two white hairs have sprouted where the stem of the cannabis plant meets the branches.  This early development can serve as a kind of pre-flowering phase; clearly, some bud development is underway.
  • The second phase of the flowering stage – which can last one to three weeks – sees further development of these white hairs.  They will begin to grow from the nodes that flourish in the corners of the branches, and at intervals up the length of the branches.  The calyxes – the actual “flower” of the cannabis – begins to develop, along with extra, supportive leaves, and resin glands known as trichomes.  Buds will also begin to fill the “internodal space” between the separate nodes.
  • By the third phase of the flowering stage, the buds are dense and thick, as are the trichomes.  The cannabinoids – THC, CBD, and others – are building up within and around the buds.  The plant will put on a lot of its final weight during this phase, which can last anywhere from two to five weeks.  Close attention should be paid to heat, as too much can cause the buds to stretch – called fox-tailing – making them “airy” and less potent.
  • The last phase occurs when it is nearly time to harvest the cannabis buds.  The flowering stage is drawing to a close, as indicated by the deterioration of the white hairs – they will darken and begin to curl.  The trichomes will become white, and the resin coating on the leaves and buds should begin to turn amber in colour.  When much, but not all, of the resin is amber and about 70% of the hairs have darkened, it is time to harvest the cannabis buds.  Too much later, and the buds will be overripe.

    During this final phase of the flowering stage, many growers recommend ceasing all nutrients.  Watering with neutral pH water over the last one or two weeks can ensure remaining nutrients have been flushed from the plant, improving the taste of the buds.  The cannabis crop can now be harvested, dried, and consumed.

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