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best npk for flowering cannabis

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.

Best NPK Ratio for Veg and Flower

Waiakeauka
Well-Known Member
scunkworm
Active Member
scunkworm
Active Member
elduece
Active Member
homebrewer
Well-Known Member

Your info is pretty mixed up there. 3-1-2 for veg though I’ve found 1-1-1 works just as well. 1-3-2 for flower is by far the best NPK ratio I’ve tried thus far.

Too much P locks out Zinc, Iron, and Copper. Not sure where you’re getting N from.

cannabis love
Well-Known Member
Rotweiller
Well-Known Member

Hello Waiakeauka. I’m not sure if this will help you or not but i found this on another website and it made sense to me –
Cannabis requires a 1:2 ratio of P to K throughout all stages of it’s growth.

It’s worth stating for the record the actual ratios of N, P and K that cannabis requires through it’s life cycle:

Vegetative Stage
N – P – K
3 – 1 – 2

Flowering Stage
N – P – K
1 – 1 – 2

Final Flowering Stage
N – P – K
0 – 1 – 2

To translate this into a 12 week schedule for a typical Skunk type such as Cheese or Psychosis would give something along these lines:

Veg week 1: 3 – 1 – 2
Veg week 2: 3 – 1 – 2
Flo week 1 : 3 – 1 – 2
Flo week 2 : 3 – 1 – 2
Flo week 3 : 1 – 1 – 2
Flo week 4 : 1 – 1 – 2
Flo week 5 : 1 – 1 – 2
Flo week 6 : 1 – 1 – 2
Flo week 7 : 0 – 1 – 2
Flo week 8 : 0 – 1 – 2
Flo week 9 : 0 – 0 – 0
Flo week 10: 0 – 0 – 0

This schedule reduces the Nitrogen two weeks into the 12/12 period which will assist in stopping the vertical growth (stretch). It cuts out all Nitrogen after 6 weeks which will result in a less leafy, smoother burning end product with greater density to the flowers. The last two weeks of plain water is sufficient to leach out all accumulated salts and give a clean end product. Three week flush as advocated by some really isn’t necessary if the Nitrogen is cut out after 6 weeks. The people using a three week flush tend to use Canna nutes which have too much N in them for late flowering and this is why they get a benefit from flushing for three weeks.

Hope that makes sense. Despite all the crap the nute companies fill our heads with about the need for all kinds of fancy bottles, you really don’t need any of them. Cannabis is a simple plant, a weed in fact, and all it needs is the correct NPK at the correct time plus a full range of trace elements, that is hard fact and no amount of BS an marketing from the nute companies will ever change that fact.

Anyway Hope this helps you a little bit ? Good luck and Happy Growing

uhavealighter?
Active Member

Hello Waiakeauka. I’m not sure if this will help you or not but i found this on another website and it made sense to me –
Cannabis requires a 1:2 ratio of P to K throughout all stages of it’s growth.

It’s worth stating for the record the actual ratios of N, P and K that cannabis requires through it’s life cycle:

Vegetative Stage
N – P – K
3 – 1 – 2

Flowering Stage
N – P – K
1 – 1 – 2

Final Flowering Stage
N – P – K
0 – 1 – 2

To translate this into a 12 week schedule for a typical Skunk type such as Cheese or Psychosis would give something along these lines:

Veg week 1: 3 – 1 – 2
Veg week 2: 3 – 1 – 2
Flo week 1 : 3 – 1 – 2
Flo week 2 : 3 – 1 – 2
Flo week 3 : 1 – 1 – 2
Flo week 4 : 1 – 1 – 2
Flo week 5 : 1 – 1 – 2
Flo week 6 : 1 – 1 – 2
Flo week 7 : 0 – 1 – 2
Flo week 8 : 0 – 1 – 2
Flo week 9 : 0 – 0 – 0
Flo week 10: 0 – 0 – 0

This schedule reduces the Nitrogen two weeks into the 12/12 period which will assist in stopping the vertical growth (stretch). It cuts out all Nitrogen after 6 weeks which will result in a less leafy, smoother burning end product with greater density to the flowers. The last two weeks of plain water is sufficient to leach out all accumulated salts and give a clean end product. Three week flush as advocated by some really isn’t necessary if the Nitrogen is cut out after 6 weeks. The people using a three week flush tend to use Canna nutes which have too much N in them for late flowering and this is why they get a benefit from flushing for three weeks.

Hope that makes sense. Despite all the crap the nute companies fill our heads with about the need for all kinds of fancy bottles, you really don’t need any of them. Cannabis is a simple plant, a weed in fact, and all it needs is the correct NPK at the correct time plus a full range of trace elements, that is hard fact and no amount of BS an marketing from the nute companies will ever change that fact.

Anyway Hope this helps you a little bit ? Good luck and Happy Growing

I back this statement up for sure! I have seen many experiments where people are trying to compare advanced nutrients to other nutes and this company has always clearly won. Mostly because their nutrients were developed from cannabis and not tomatoes. Maybe we should blend cheaper nutes to the AV’s npk ratios? I believe it would be their n-p-k ratios over anything else. They do also have a lot of boron probably for some good reason.

All of their nutrients schedules for the flowering stage, with additives or without, comes very close to 1-1-2-0.5 Ca-0.25 Mg. At the last two weeks, however, they have it closer to 2-3-4-1 Ca-0.6 Mg. And obviously a flush at the end.

Advanced Nutes seems to have a lot of amino acids, humic acid, sugars, and microbes too.

I also like that they don’t have calcium mixed with phosphorous and magnesium in concentration.

But I will stay away from them and mix up cheap, microbe friendly nutes using AV’s ratio’s.

There have been many people that say you need to use nutes that are designed for MJ, so what is the ideal NPK ratio for Veg and Flower? Many people say…