NPK for Cannabis - recent studies

cobshopgrow

cobshopgrow

Well-Known Member
It looks like there are new studies made on cannabis i have missed so far.
Am curious to hear your opinions, especially for K.

A little compilation.

Scientifically-Based Optimal NPK Levels for Cannabis
Sources: Caplan et al. (2017–2018, Univ. of Guelph), Bernstein et al. (2020–2021, Israel), Zamlout et al. (2022, Front. Plant Sci.), Saloner & Bernstein (2021, MDPI Agronomy)

Growth (Vegetative Phase):
  • Nitrogen (N): 100–160 ppm
  • Phosphorus (P): 20–40 ppm
  • Potassium (K): 60–100 ppm

Flowering Phase:
StageN (ppm)P (ppm)K (ppm)
Early Bloom80–10030–5080–120
Late Bloom30–5020–4060–100

Notes:
  • ⚠️ Excess N (>160 ppm) can reduce biomass (Caplan et al.)
  • ⚠️ Excess K (>120 ppm) may reduce cannabinoids and terpenes (Bernstein et al.)
  • ⚠️ P above 60 ppm shows no benefit (Zamlout et al.)

pH & EC Targets:
  • Soil: pH 6.0–6.5 | EC 1.2–1.8 mS/cm
  • Coco: pH 5.8–6.2 | EC 1.6–2.2 mS/cm
Peer-reviewed studies on cannabis nutrient optimization:


• Caplan et al. (2017) – Optimal nitrogen levels in vegetative phase
HortScience 52(11)
https://doi.org/10.21273/HORTSCI12310-17


• Caplan et al. (2018) – Drought stress increases cannabinoids
HortScience 53(5)
https://doi.org/10.21273/HORTSCI12847-18


• Bernstein et al. (2019) – Mineral nutrition vs. secondary metabolite profile
Frontiers in Plant Science
doi.org

Frontiers | Impact of N, P, K, and Humic Acid Supplementation on the Chemical Profile of Medical Cannabis (Cannabis sativa L)​

Mineral nutrition is a major factor affecting plant growth and function. Increasing evidence supports the involvement of macro and micronutrients in secondar...
doi.org
doi.org


• Bernstein et al. (2020) – Excess potassium reduces cannabinoids & terpenes
Industrial Crops and Products 145
Redirecting


• Saloner & Bernstein (2021) – Nitrogen effects under long-day conditions
Plants 10(3): 559
https://doi.org/10.3390/plants10030559


• Zamlout et al. (2022) – Phosphorus above 60 ppm gives no benefit
Frontiers in Plant Science 13
https://doi.org/10.3389/fpls.2022.834435



Summary:
These peer-reviewed studies show that cannabis:


  • Grows best with moderate N (100–160 ppm)
  • Does not benefit from excess P (>60 ppm)
  • Loses quality with excess K (>120 ppm)
  • Requires balanced micronutrients, especially Ca, Mg, Fe
 
thanks, i will have a look.
"new" is of course relative, to my feeling things moved a bit in the last good 5y.
keypoint is somehow, much P and K isnt what we may looking for, hard to say for me, always gave a good amount PK.
 
cobshopgrow said:
thanks, i will have a look.
"new" is of course relative, to my feeling things moved a bit in the last good 5y.
keypoint is somehow, much P and K isnt what we may looking for, hard to say for me, always gave a good amount PK.
Click to expand...
It kinda cemented some thoughts I’ve had regarding P&K. I’ve always thought we overfertilized P/K, and were a little light on N, particularly in bloom/late bloom. IMHO, I think that that a lot of the plants we thought had deficiencies, actually had toxicities.
 
Phytoplankton said:
It kinda cemented some thoughts I’ve had regarding P&K. I’ve always thought we overfertilized P/K, and were a little light on N, particularly in bloom/late bloom. IMHO, I think that that a lot of the plants we thought had deficiencies, actually had toxicities.
Click to expand...
yes, i think i observed quite some K toxicites also.
 
ve just been reading up essential oil making and how to increase plant oils, nitrogen is the important factor in oil production, too much and you get less oils and of lower quality as well as amount, to little and you get a stunted plant with less oil of lower quality, so those new limits are fantastic to know. many thanx
 
most of you more experianced growers have there grow enviroment dialed in, this is mostly for those who dont

To increase essential oils in plants for extraction, focus on optimizing growing conditions and using specific extraction techniques. For example, plants can produce more essential oils when exposed to conditions like sunlight and specific soil conditions. Microbial fertilizers and innovative extraction methods like microwave extraction can also enhance essential oil production. Steam distillation is a common and effective method for extracting essential oils, particularly when using a still or a crockpot.

Here's a more detailed look at how to increase essential oil content and extraction methods:

1. Optimizing Growth Conditions:
  • Sunlight:
    Increased sunlight exposure can stimulate the production of essential oils in plants.

  • Soil:
    Nutrient-rich soil and proper pH levels can also contribute to higher essential oil content.

  • Watering:
    Consistent and appropriate watering is crucial for plant health and essential oil production.

  • Fertilizers:
    Using microbial fertilizers can provide beneficial nutrients for plant growth and increase essential oil production.

  • Harvesting:
    Harvesting plants at the optimal time, typically when they are in full bloom, can yield the most essential oils.
2. Extraction Techniques:
  • Steam Distillation:
    This is the most common method, where steam is passed through plant material to release essential oils. The resulting vapor is then condensed, and the essential oil separates from the water.

  • Hydrodistillation:
    Similar to steam distillation, this method involves boiling the plant material in water to release the essential oils.

  • Cold-Press Extraction:
    This method is used for citrus peels and other plant materials where heat is not ideal.

  • Microwave Extraction:
    This method is gaining popularity for its ability to speed up extraction and potentially enhance essential oil quality.

  • Other methods:
    Squeezing, enfleurage, and solvent extraction are also used for specific types of essential oils and plant materials.
3. Factors Affecting Essential Oil Content:
  • Plant Species: Different plants have varying essential oil concentrations.

  • Plant Age and Stage of Growth: Essential oil content can fluctuate depending on the plant's stage of development.

  • Environmental Factors: Temperature, humidity, and sunlight can affect essential oil production.

  • Soil Composition and Nutrients: The quality of the soil and the availability of essential nutrients can influence essential oil content.

  • Harvesting and Processing Methods: The way plant material is harvested and processed can impact the quality and yield of the essential oil.
 
OneHitDone said:
What are your thoughts on the K:Ca:Mg ratio?
Click to expand...
„Potassium concentrations exceeding 120 ppm in the fertigation solution caused a decline in cannabinoid and terpene content. Balanced Ca and Mg mitigated the antagonistic effects.“

3:2:1 is about ideal, but its ok to go higher with the Ca:Mg ratio as far i understood.
so 3:3:1.5 is ok too as long K supply is high enough and the Ca:Mg level is not interfering with other nutrients.
 
cobshopgrow said:
yes, i think i observed quite some K toxicites also.
Click to expand...

Few years back I tried some NPK levels which were from similar researches.
The 5:1:5,5 NPK, which is something like Maxigro, has way too much N and K.
I'd get N toxicity and Ca deficiency (likely due to excess K).

Though the plant uses less N and more of P,Ca very early in veg while focus is on establishing roots.
But I reckon something like 3:1:2 would be good for vegging.

During the flower stretch phase (1-3weeks), plant is very inclined for P deficiency especially closer to the 2-3weeks.
For the 1-3weeks I go 1:1:2 or 1:1:1 (similar ratio what I would prefer for early veg).

Then taper down the N a bit and support flower development with some extra K. P somewhat steady.
So 3-5weeks I aim for around 1:2:3.

Might tune it for late flower as 1:2:4.

As for K:Ca:Mg:

for vegging 1:1:0,5
When stretch phase is ending start increasing the K:Ca ratio from 1:1 veg to late flower of 3:1.

Also obviously plenty variation between the strains etc, but this is starting point for me.
 
cobshopgrow said:
„Potassium concentrations exceeding 120 ppm in the fertigation solution caused a decline in cannabinoid and terpene content. Balanced Ca and Mg mitigated the antagonistic effects.“

3:2:1 is about ideal, but its ok to go higher with the Ca:Mg ratio as far i understood.
so 3:3:1.5 is ok too as long K supply is high enough and the Ca:Mg level is not interfering with other nutrients.
Click to expand...

K:Ca:Mg absorption is very connected to each other.
Too much of any of the 3, reduces uptake of the other 2.

And while K and Mg can redistribute themselves well within the plant, calcium will not move well.
Also calcium uptake is mostly affected by the transpiration.
 
cage said:
Few years back I tried some NPK levels which were from similar researches.
The 5:1:5,5 NPK, which is something like Maxigro, has way too much N and K.
I'd get N toxicity and Ca deficiency (likely due to excess K).

Though the plant uses less N and more of P,Ca very early in veg while focus is on establishing roots.
But I reckon something like 3:1:2 would be good for vegging.

During the flower stretch phase (1-3weeks), plant is very inclined for P deficiency especially closer to the 2-3weeks.
For the 1-3weeks I go 1:1:2 or 1:1:1 (similar ratio what I would prefer for early veg).

Then taper down the N a bit and support flower development with some extra K. P somewhat steady.
So 3-5weeks I aim for around 1:2:3.

Might tune it for late flower as 1:2:4.

As for K:Ca:Mg:

for vegging 1:1:0,5
When stretch phase is ending start increasing the K:Ca ratio from 1:1 veg to late flower of 3:1.

Also obviously plenty variation between the strains etc, but this is starting point for me.
Click to expand...
When talking NPK ratios (3-1-2 etc) are you talking about the ratio of the elemental ppm's or the "NPK Ratio's"? If the later, are you correcting for the P205 and K2O reductions?
 
cobshopgrow said:
„Potassium concentrations exceeding 120 ppm in the fertigation solution caused a decline in cannabinoid and terpene content. Balanced Ca and Mg mitigated the antagonistic effects.“

3:2:1 is about ideal, but its ok to go higher with the Ca:Mg ratio as far i understood.
so 3:3:1.5 is ok too as long K supply is high enough and the Ca:Mg level is not interfering with other nutrients.
Click to expand...
Where do your EC levels typically land at your target ppm's?
 
really depends, for my recent grow.
i just do soil grows atm with organic dry fertilizer.
my tap is EC 0.7, 110ppm of it are Ca (CaCo3 so 70ppm avaiable Ca), only 9ppm are Mg, so some Epsomsalt is sensefull (while not needed on every watering in soil).
maybe 0.2 to 0.5g a liter (for me), raising the EC not that much.
in regards of K in can only see to pick a dry fertilizer with some lower K content, so far i use 5-3-7 and think that its may not ideal, idk.

for a mineral mix a target EC based on, lets say 120ppm N, 45 P, and 120 K, 80 Ca (60 seems low to me 2:1), 40 Mg would be about EC 2, ion specific and will read as a 1.6-1.8 on your meter.

i havent tested such a mix myself, ymmv.
 
Delps8 said:
I'll toss these in the mix.

One of them is the paper by Saloner, Sacks, and Bernstein but the others are "new".
Click to expand...
most "eye opening" to me is this one (seems my links above are all a bit f... up, sry).

"The improved physiological state under 60–175 mg L−1 K enabled higher biomass and yield production, but K supply above 60 mg L−1 K did not affect yield production (Figure 2). The highest K treatment of 240 mg L−1 K negatively influenced most physiological parameters in DQ compared to the lower K levels, while the cultivar RM did not suffer from excess K supply (Figure 9; Figure S4 Supplemental). K over-supply normally does not induce physiological damage to plants [16,28,49]. Thus, the detrimental effects of high K inputs (at 240 mg L−1 K) on the physiological function of the cultivar DQ were surprising. The adverse effects of K over-supply can be best explained by the substantial reduction in the accumulation of Ca and Mg in the leaves (Figure 7 and Figure 8), as a shortage of Ca and Mg in leaves is a known cause of physiological damage [50,51,52,53]."

maybe some i have overlooked all the years.
sure, its cultivar specific, but seeing especially no benefit on the high THC cultivar in the study is may a hint.
 
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