Scientists at the University of Guelph in Canada are staking their claim to what they believe is a first in the scientific community. That is, the first-ever ‘weed paper’ published on the topic of growing cannabis.
“Growing marijuana has been illegal for so many years that there has been hardly any scientific research up until this point on how to produce this crop,” said Prof. Youbin Zheng. “There has been no science guiding this industry.”
All due respect to the professor, but brushing off the entire millennia-long history of human cannabis cultivation as unscientific? Wut? The many incredible growers around the world, who’ve succeeded at making cannabis ever more potent and therapeutic, might beg to differ.
Indeed, marijuana cultivators have researched and developed countless, invaluable improvements to the science of growing weed.
And for at least a century, in North America at least, they’ve done it under prohibition. They just don’t chair university horticulture departments and publish their findings in scholarly journals.
But giving Zheng some slack, he and his team have broken important ground in the scientific community.
So what does this first-ever ‘weed paper’ say? Does it confirm or contradict what professional and amateur growers have already figured out?
And for all you home-growers out there, read on to learn the exact measurements for ideal indoor grow conditions.
First-Ever ‘Weed Paper’ Reveals Ideal Substrate and Fertilizer For Growing Indoors
First, let’s start with what Prof. Zheng, along with Prof. Mike Dixon and PhD horticultural student Deron Caplan, actually studied.
Scientific research is all about controlling for variables in order to know, with some certainty, which causes produce which effects. There’s no way Zheng and his team could study all the variables that go into growing cannabis at once.
So they started with nutrition.
Specifically, they set out to find the ideal fertilizer rate and the ideal grow medium for Cannabis sativa in its vegetative state. In other words, the period of the plant’s growth before it flowers.
Zheng and the other researchers were looking for how combinations of those two factors influenced the concentration of THC in dried floral material.
First-Ever ‘Weed Paper’ on Ideal Indoor Grow Conditions: By The Numbers
Zheng’s first-ever ‘weed paper,’ published in the journal HortScience, explained the process.
Using liquid organic fertilizer with a PKN ratio of 1.3P–1.7K-4.0N, the experiment tested five increasing rates of fertilization.
They also tested two coir-based soil-less growing media, or “substrates.”
And there’s the first interesting convergence with popular wisdom about growing cannabis. Coir-based grow media, like coco-coir, are surging in popularity among cannabis growers.
And no wonder; they produce results. The first-ever ‘weed paper’ says the same thing: coir-based substrates are the best, and absorption doesn’t matter so much.
The difference between the two coir substrates tested was their water-holding capacity, or WHC. Between lower and higher WHC substrates, the team found no difference. The researchers used ABcann UNIMIX 1/1-HP for their soil-less substrate.
And when it comes to the fertilizer rate, the team found that
“the highest yield, cannabinoid content, and plant growth were achieved around an organic fertilizer rate that supplied 389 mg N/L during the vegetative growth stage…”
That’s 389 milligrams of nitrogen per liter of water, or mg N/L.
Again, no surprise there. Marijuana growers know that more nitrogen is generally a good thing for yield and potency. But, they also know you can poison weed plants with too much of it.
Zheng et al. might concur.
Their magic 389 mg N/L was just a shade over the middle of the range they tested, which ran from 117 to 585 mg N/L.
The paper does note that pushing the fertilizer rate up to 418 mg N/L maximized THC concentrations in dried flower. But that came at the expense of yield and other cannabinoid content.
What’s Next For The Researchers Who Published The First-Ever ‘Weed Paper’ on Growing Marijuana
Having figured out the ideal conditions for indoor growing during the cannabis plant’s vegetative stage, Zheng and Dixon are setting their sights on the flowering stage next.
In their next weed paper, which will appear in the same journal, the researchers hope to publish findings about the experiments they are currently conducting.
These new tests are studying the ideal lighting and irrigation conditions for flowering cannabis plants.
The goal is to dial in the ideal light spectrum for high-yields of cannabidiol (CBD). CBD is the non-psychoactive cannabinoid which studies continue to link to numerous medical and therapeutic benefits.
Even beyond improving the science of growing weed, Zheng believes this research has applications in agriculture more generally. He’s hopeful the findings could also help us produce food more efficiently, in addition to growing incredible weed.
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