Alright, so what is the consensus on potassium in the flowering stage?
I’ve been “doing my own research” on nutrient compositions of various solutions used on cannabis plants in industry and in scientific papers. After all my reading I’m starting to wonder if the hype with high potassium concentrations at the flowering stage is bullshit. Let me be clear - when I say HIGH potassium concentrations I’ve seen people say to just drop nitrogen and phosphorus out of the equation and hit it with a high potassium dose - Not sure what ppm people are talking about.
Here are some things I think are important about Nirit’s research (personal friend and imo great researcher):
The setups are pure perlite drain to waste at EC values normally in the 1.3-1.8mS/cm range.
The setups have no CO2 enrichment.
Efforts in this study are made to keep nutrient values consistent between runs. Meaning she will do a big effort to only change K between treatments and keep everything else as close to unchanged as possible.
Her base nutrient ratios are different from what commercial cannabis fertilizers generally use. These are concentrations derived from optimal values found in her previous research papers.
There is no change in the solutions through the entire life of the crop in flower - each treatment is maintained for the entirety of the plant’s short day cycle - nor are there changes in the environment, nutrient strength or irrigation schedules as a function of time.
The strains she uses are quite different from the average strains used in the US west coast, quite low THC in comparison.
When you consider all the above and you consider how K is traditionally increased in grows - the salts used to achieve this, the base ratios and how nutrient ratios are affected by these additions - several clear differences appear.
While Nirit’s research conclusions are very solid for her setup and conditions, it is very important to consider how these conditions differ from the average commercial growing setup in North America.
When you interpret research, Nirit’s or anyone else’s, it is very important to evaluate how the conclusions made relate to the conditions of the research and what limitations there might be in expanding those conclusions to other growing conditions and environments.
So how well do the conclusions on this paper hold for your grow? Think about how closely you resemble Nirit’s experimental setups and which variables differ that might cause things to change.
Especially think about how you exactly achieve K increases, which counterion to K you use and how this affects ratios and concentrations with other nutrients. Also consider whether other changes are done at the same time as K changes.
K is extremely important to brix and metabolism… Even though the plant tissue dosent contain much potassium I would say it’s probably the most important nutrient. It can be charged, and it can move other compounds around the plant. It plays a vital role in flavor and aroma compounds. I wouldn’t say potassium is not important in flower.
If I’m not seeing the potassium droop at night in early flower I’m usually not happy, and I usually don’t get bleeding sugar
In my research I discovered a trend of lower K and higher P at transition (week1-3). Then lower P and higher K during the “fruit fill” stage, week 4 and later for shorter flowering cultivars. I’ve found N should be lower at transition and higher during fruit fill. The high N in transition will slow the flowering time of the plant and kind of dud the flower sites, but it’s safe the bring the N back up a bit until about the last week of flower when you want to start backing off nutrients a bit (not flush).
So, I think of the later part of flowering almost as second a vegetative stage, because the plant is done with its hormonal changes and starts growing almost in a vegetative way again.
It’s actually a bit more complex than that, but I doubt theres much economic advantage to dialing it in anymore precisely. I’d recommend checking out John Kempf’s Points of Critical Influence. He uses plant sap analysis, the most accurate method of analyzing plant nutrition and health in my opinion. Most plants follow the same nutrient requirement patterns based on lifecycle, not just cannabis. Hope that helps!