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Complete Guide To The Cannabis Flowering Phase

We guide you through the cannabis flowering phase, from the first week all the way to harvest.

  • 1. Entering the flowering phase
  • 2. Weeks 1–3
  • 2.a. Best practices
  • 2.b. Nutrients, temperature, lighting, and humidity
  • 3. Weeks 3–4
  • 3.a. Best practices
  • 3.b Nutrients, temperature, lighting, and humidity
  • 4. Weeks 4–6
  • 4.a. Best practices
  • 4.b. Nutrients, temperature, lighting, and humidity
  • 5. Weeks 6–8
  • 5.a. Best practices
  • 5.b. Nutrients, temperature, lighting, and humidity
  • 6. Don’t rush to harvest
  • 1. Entering the flowering phase
  • 2. Weeks 1–3
  • 2.a. Best practices
  • 2.b. Nutrients, temperature, lighting, and humidity
  • 3. Weeks 3–4
  • 3.a. Best practices
  • 3.b Nutrients, temperature, lighting, and humidity
  • 4. Weeks 4–6
  • 4.a. Best practices
  • 4.b. Nutrients, temperature, lighting, and humidity
  • 5. Weeks 6–8
  • 5.a. Best practices
  • 5.b. Nutrients, temperature, lighting, and humidity
  • 6. Don’t rush to harvest

Ahhh, the bloom phase. After weeks of caring for your ladies, pruning and training them in order to promote as much vegetative growth as possible, it’s time to turn your focus to helping them flower. In this article, we’ll show you exactly how to do that.

ENTERING THE FLOWERING PHASE

When exactly your plants are ready to flower will depend on a number of factors. If you’re growing outdoors, your ladies will only start flowering toward the end of the summer when the days naturally get shorter. If you’re growing indoors, you’ll have a lot more control over your plant’s flowering phase. Most growers will move their plants into bloom after about four weeks of vegetative growth, but you can technically keep them in this phase indefinitely.

Once your plants receive less light, they’ll automatically start focusing their energy on growing buds rather than foliage. For the best possible harvest, you’ll want to help them along with the right nutrients, lighting, and environmental conditioning.

Below is a detailed overview of a regular eight-week flowering period. While some strains have shorter and/or longer flowering times, this guide will help you understand what to expect as your plants approach harvest, and what you can do to maximise the quality of the buds they produce during this vital stage.

Flowering phase (Week 1) Flowering phase (Week 2) Flowering phase (Week 3) Flowering phase (Week 4)
Flowering phase (Week 5) Flowering phase (Week 6) Flowering phase (Week 7) Flowering phase (Week 8)

WEEKS 1–3

• What to expect: Flowering stretch, white hairs (pistils), and noticeable aromas.

Many growers think that as soon as they flip their plants into flower, they’ll stop growing and start developing buds. But that couldn’t be further from the truth.

During the first week or so of flowering, plants will actually experience a period of accelerated growth and stretching. This “flowering stretch” is completely normal as they try and outgrow surrounding vegetation in order to get the most sun possible to ensure higher chances of reproduction—plus, a longer internodal distance means more space for flower clusters, and better light penetration. Just how much growth you can expect to see during this first week will vary depending on what strain you’re growing, but some strains can almost double in height during this time.

Week two of flowering is usually when you can confidently “sex” your plants. Females will start growing long, white pistils at their nodes (bud sites). Males, on the other hand, will develop round pollen sacs. If you’re growing from regular seeds, make sure to sex your plants early and separate your males and females quickly to avoid pollination (unless you’re breeding, of course).

By week three, your plants will gradually stop stretching and really focus on developing their buds. While the buds will still be small, you’ll notice larger calyxes and the development of some trichomes.

BEST PRACTICES

Nutrients: A cannabis plant’s nutrient requirements will change dramatically as it starts flowering. In this early stage, your plants will respond well to nutrient solutions with higher concentrations of phosphorus and potassium. What exact NPK formula you go with is up to you—just be careful not to go too heavy during this preliminary stage to avoid burning your plants. At what stage you decide to drive up your nutrients is also up to you, but we recommend doing so during week two.

Overfeeding/deficiencies: Properly shifting from veg to bloom nutrients can be tricky, especially if you’re a rookie grower. Make sure to keep a close eye on your plants and look out for signs of deficiencies or overfeeding (dead, burnt, or yellow foliage).

LST: Low-stress training can be a great way to manipulate your plants and deal with the added stretching of the early flowering phase. LST will also help you create an even canopy and ensure your plants’ lower buds get enough light.

Temperature: Cannabis responds well to cooler temperatures during the flowering stage. Each plant will be a little different, and every grower will have their own advice on finding the perfect temperature for flowering. However, we recommend keeping daytime temperatures around 26°C and nighttime temperatures around 16–18°C. Keeping your nighttime temperatures relatively low is super important for better bud development.

NUTRIENTS, LIGHTING, TEMPERATURE, AND HUMIDITY

EC
1.2–1.5
HUMIDITY
50–60% RH
TEMPERATURE (Day/Night)
26°C / 16–18°C

WEEKS 3–4

• What to expect: Bigger buds and more intense aromas.

By weeks 3 and 4, your cannabis plants will have stopped growing altogether and will be focusing entirely on developing buds. You should notice their flowers getting bigger on a daily basis, developing thick calyxes, more white pistils, and a nice layer of trichomes. Your plants will also start taking on more noticeable, complex aromas.

BEST PRACTICES

Feeding: As your plants grow bigger buds, they’ll need more nutrients. Again, the exact nutrient solution you use during this stage of flowering is up to you, but make sure to pay close attention to how your plants react to any changes in feeding. A common NPK formula used during mid-flowering is 6-15-10.

Humidity and airflow: It’s really important to keep an eye on humidity and airflow. Stagnant, humid air creates a breeding ground for mould and bacteria, and also attracts pests. To be in the clear, we recommend keeping your relative humidity at 40–50% and using fans or ventilation to keep air circulating around your grow room.

NUTRIENTS, LIGHTING, TEMPERATURE, AND HUMIDITY

EC
1.5 approx.
HUMIDITY
50% RH
TEMPERATURE (Day/Night)
24-26°C / 16–17°C

WEEKS 4–6

• What to expect: Full-throttle flowering and big, dense buds. Aroma will be nearing its peak.

By weeks 5 and 6, your plants will be well into flowering. Their buds should be big, thick, and loaded with white pistils. They will also be developing a thick coat of trichomes, which should be giving off a nice, pungent aroma. If you haven’t invested in an extractor and air filter by now, this might be a good time to do so.

If you take a closer look at your buds, you should notice some pretty drastic changes from how they looked a few weeks back. The calyxes should be notably larger, and the buds should look and feel denser and heavier. Some fast-flowering strains may be approaching harvest time already, in which case the buds should look even more mature (with more trichomes and darker-coloured pistils).

BEST PRACTICES

Feeding: This period (weeks 5 and 6) is considered peak flowering time for most cannabis strains. Make sure to keep a very close eye on your plants and look out for any signs of nutrient deficiencies or overfeeding. Depending on the size of your buds, you may want to dial up your nutrients one more time to help them produce the best possible harvest. Remember that, by this stage, your plants won’t need much nitrogen, which is more important for vegetative growth rather than blooming. Besides phosphorus and potassium, flowering plants have higher demands for calcium.

Stress: Whatever you do, you’ll want to avoid stressing your plants during this stage to prevent stunting the growth of their buds or, even worse, triggering hermaphroditism. Stress can trigger flowering females to produce pollen and self-pollinate in one final attempt to reproduce before dying.

Support: You’ll be surprised by how heavy fresh cannabis flowers can be. If your plants are struggling to support the weight of their flowers, consider using bamboo stakes and string or plant clips to keep your plants upright and prevent them from tumbling over.

Humidity and temperature: Keep humidity at around 30–40% from here on out to avoid any problems with mould or pests. Also, keep your daytime temperatures at 25°C max, and nighttime temperatures around 16–17°C.

NUTRIENTS, LIGHTING, TEMPERATURE, AND HUMIDITY

EC
1.5–1.6
HUMIDITY
30-40% RH
TEMPERATURE (Day/Night)
24-26°C / 16–17°C

WEEKS 6–8

• What to expect: Last stages of bloom and harvest.

Weeks 6, 7, and 8 make up the final stages of flowering for most strains. By this stage, the buds on your plants should be dense, firm, and coated with a thick layer of trichomes. The trichomes should be transitioning from completely clear to milky white, with a select few turning amber. This is a telltale sign harvest is here. You can verify this by “zooming in” on them using a pocket scope or magnifying glass. The pistils will continue to get darker during these final weeks too—another sign that your plants are almost ready for harvest.

In these final weeks, phosphorus, potassium, and calcium are still your most important nutrients. Two weeks before harvest, however, you’ll want to flush your plants with plain, pH-balanced water. This encourages them to take up all remaining nutrients, and helps preserve the natural flavour of your buds.

During this last flush, your plants will develop some yellow leaves as they consume all the remaining nutrients stored in their foliage.

Again, your buds will be ready to harvest once the majority of trichomes have turned milky white. Weed harvested earlier tends to have more of an uplifting, euphoric effect. On the other hand, weed harvested later tends to produce a more relaxing, sleepy stone. Although it hasn’t been comprehensively verified, it is believed that cannabis plants produce more CBN (degraded form of THC) and myrcene toward the end of their life cycle.

BEST PRACTICES

Nutrient flush: Always remember to flush your plants with pH-balanced water two weeks before you harvest.

Humidity: Keep humidity between 30–40% max to avoid problems with mould or pests.

Bud maturity: Keep a close eye on your plants during your two-week flush. You’ll know your buds are ready to harvest using the trichome method described above.

48–72 hours of darkness: To try and raise the potency of your weed, consider leaving your plants in complete darkness for a full 48–72 hours before harvest. Some growers swear by this trick, claiming it helps plants produce more trichomes, resulting in more potent weed.

Are your cannabis plants starting to flower? Click here to learn all there is to know about the cannabis bloom phase and how to maximise your harvest.

The flowering stage

The plant is fully grown and the end is nearly in sight. Now we are approaching the flowering phase, after which you can start harvesting. The first three weeks of the flowering stage are in fact more a growth phase. After the flowering period of the plants has been initiated by setting the lighting to a schedule of 12 hours light and 12 hours darkness, they will start flowering and buds will start growing explosively. In which week of flowering do the buds grow most depends on the strain and type of cannabis plant you are growing. They can easily double or even triple in size. I remember the first time I ever grew a plant as if it was yesterday. I was amazed to see that the little plant quickly transformed into a giant. The buds keep swelling, the trichomes start being formed and the specific odor of the plant continues to develop, which makes it hard to wait until the buds can be harvested and you can enjoy the first joint of your own harvest.

Grow and bloom fertiliser

During the flowering phase, you have to switch to bloom nutrients. Some growers keep giving their plants grow fertilizer in the first and sometimes in the second week of the flowering phase because it is a kind of transition period and the plants still need building blocks to grow quickly. This will make the plants grow a bit taller. It all depends on what you want. By managing your use of fertilizer, you can control the size of your plant. If your plants already have the right size and you want to keep them smaller (because for instance space is limited), immediately start giving them bloom fertilizer. If your plants are still a bit small and space is not used optimally, you can continue administering grow fertilizer. They will grow a bit taller. The differences are not extreme, but a couple of centimeters can make quite a difference.

Bloom nutrients

After a blooming period of three weeks, the plants have achieved their maximum size. They will no longer grow in height and width but will start forming buds. It is really important to administer blooming nutrients then because the plants need more phosphorus and potassium. These are important building blocks for a good bud formation. PK 13/14 is a mixture high in phosphorus/potassium that stimulates flowering and fruiting. It is usually indicated on the bottle how much you have to administer. Make sure you do not give the plants too much, otherwise you risk overfertilizing them.

Suzy’s Tip: Watch your plant closely and try to tell what it needs. Every plant blooms in its own way, so in some strains, the buds will grow from the beginning, while in other strains they will only grow in size and weight in a later stage. The needs of the plant can also change after a couple of weeks.

Foliar feeding

If you fertilize well, you actually don’t need foliar feeding. Unfortunately, it is very hard to fertilize flowering cannabis well. Even if you think that you are giving the right nutrients, the plants may lack something. If so, you can administer foliar feeding to your plant. The nutrients are rapidly absorbed in this way and any nutritional deficiencies are corrected quickly. The chance of overfertilizing is minimal when administering foliar feeding. When growing inside, the best moment to administer foliar feeding to your plants is half an hour before the lamps go on. The light of the lamps is very powerful from the beginning, so you run the risk of burning the leaves if they are still too wet. Outdoor plants are best being administered foliar feeding early in the day, before the sun is too strong. It’s no use giving them feeding when there is no light because then the plants don’t grow and they don’t need extra feeding. Besides that, you increase the risk of mold if they are too wet. Foliar feeding has to be sprayed on top of the leaves, once or twice per week. When giving foliar feeding, you also have to watch your plant closely to discover which nutrients it needs.

Top/tie down

If space is limited, you might want to top or bind down your cannabis plants. Topping is removing the top of the plant. You will get two main tops instead of one. These do not grow as tall as one top but they yield more. You can bind a plant down by pulling the biggest bud down and binding it with slight tension. This will give you the same effect as topping, but you have the advantage that the largest bud is retained. The lower branches will develop better and the plant will grow bigger buds.

Ventilation

For a good flowering period, the plants need sufficient CO2 (carbon dioxide). They need this to grow powerfully during the hours that there is light. The more CO2 is present in the air, the faster the plants will be able to develop and the better they will be able to withstand high temperatures. You can use fans, but in good growing spaces, holes are made in the ground at one side to let air in, while at the other side an extraction system is installed as high as possible. This ensures an optimal circulation of air, from which the plants benefit by using the CO2-rich air that is continually circulating. Fresh air is continually sucked in through the holes in the ground. A fan is also very important. These do not only ensure good air circulation but also give the plants a pleasant breeze which will cause them to grow even better.

Bud formation

The period in which the buds of your cannabis plant start growing quickly is the most important in the flowering period. Depending on the strain, that’s usually after about 3 to 5 weeks also called the end of the flowering period. You can continue spraying your plant until then because the buds have not yet become hard and compact, but you shouldn’t after that. So you can opt for preventatively spraying your plant. When the buds start growing rapidly, you can’t do much more than administering nutrients and enjoying the wonderful sight of the buds that are gradually being formed. More and more white hairs will grow and the separate little buds will steadily grow inwards to form one big bud.

The flowering stage of the cannabis plants starts by setting the lighting to 12/12 hours light/darkness. As soon the flowering phase starts the buds will begin to develop.