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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.

What’s the Best NPK Ratio for Cannabis Nutrients

What’s the Best NPK Ratio for Cannabis Nutrients?

If you’re new to growing cannabis or still in the beginning phases, trying to figure out the best nutrients for your cannabis plants can be very confusing. There are so many companies making and selling nutrients: each one creating multiple types of nutrients with different purposes. The most important thing is to make sure you give your marijuana plants the right amounts of nutrients at the right time. There are two main life stages for cannabis plants, vegetative growth & the flowering stage, each stage has different nutrient requirements.

For the best npk ratio, your cannabis plants need to use the NPK Ratio Guide
Where is this information? Most nutrient bottles display 3 numbers (“2-1-6” in the pic below) , often called N-P-K, which stands for Nitrogen, Phosphorus and Potassium

Why “K” for Potassium? The atomic symbol of Potassium is “K” from Neo-Latin kalium.

In other words, you want to use a “Vegetative” (high Nitrogen) or “general purpose” nutrient formula for the first stage of life known as the vegetative stage. If using high-quality soil, you can skip vegetative nutrients for the first 3-4 weeks while your plant uses up the nutrients in the soil, otherwise you should start with vegetative nutrients around the time your plant opens its first leaves.
Use a “Bloom” (low Nitrogen) nutrient formula with plenty of P & K for the flowering stage. Start using bloom nutrients when buds start forming to make sure your plant gets plenty of Phosphorus & Potassium, which are crucial to bud development.

NPK Phosphorus Ratio

Phosphorus tends to increase the number of flowers, while Potassium helps increase the bulk/weight of flowers. Be careful, though because going overboard with either one can burn your plants!

The main thing is to avoid giving too much Nitrogen in the flowering stage, as it can discourage bud development in the flowering stage and add an unpleasant taste to buds, which is why a general purpose plant nutrient isn’t a good choice in the flowering stage.
Cannabis Growers Secret: If you find yourself in an emergency need for nutrients: Nutrients made for “cactus” or “succulents” can be used in the cannabis flowering stage, because they usually have low amounts of N and plenty of P & K.

Note: Don’t use any type of time-released nutrients (like fertilizer spikes, or “slow release” Miracle-Gro soil) because they deliver too much N in the flowering stage and may reduce bud growth.

Cannabis needs plenty of P & K to grow big buds in the flowering stage.

Using the Best Cannabis Growing Nutrients is just the beginning! There are a few more things you need to know for optimal nutrient intake.
Check the pH of your water to prevent deficiencies. It may surprise you that the most common reason growers get nutrient deficiencies is because the pH is too high or too low. This happens even if the right amounts of nutrients are present, because your weed simply cannot absorb the nutrients if the pH isn’t in the correct range.

Optimum pH for cannabis plants..
Soil: 6.0 – 7.0
Coco Coir: 5.5 – 6.5
Hydroponics: 5.5 – 6.5

Checking the pH will make a huge difference to your grow by keeping plants vibrant and healthy. It only takes a few minutes each time you water your plants! If you get a digital pH pen, it only takes seconds to test your pH!

Learn more about pH & preventing nutrient deficiencies here!

Trying to find the best NPK ratio to grow cannabis? What nutrients should you use for your strain. Nutrients used to grow big marijuana buds.