FEBRUARY 2019 • COUNTRY LIFE IN BC Science of cannabis takes centre stage

Proven facts can propel growers to new highs


ABBOTSFORD – With the legalization of cannabis on October 17, all eyes were focused on the business and social implications of the new crop.

But for Youbin Zheng, an associate professor specializing in greenhouse crops at University of Guelph’s School of Environmental Sciences, the date also opened the door to greater research opportunities. Zheng has been working with cannabis for 10 years. A chance meeting with an advocate of the plant’s medicinal properties piqued his interest, and he began studying the crop. People also began bringing plants for him to examine, given his work with greenhouse crops, but it was only with the general legalization of medical marijuana five years ago that legitimate research became possible. “So far, we still cannot grow plants on campus, so we do research with LPs (licensed producers)” he told the Canwest Hort Expo in Abbotsford at the end of September. Now, with full legalization

in place, Zheng is participating in the development of the Guelph Centre for Cannabis Research, where he plans to put many popular theories about cannabis production to the test. “We are a horticultural

university, so we cannot say no,” he says. The work is timely. With cannabis capable of generating $20,000 per square metre a year, many greenhouse growers have ditched other crops such as tomatoes, which yield a meagre $200 per square metre a year. BC has lost more than 100 acres of greenhouse vegetable production to cannabis in the past two years.

But production comes with a number of challenges because cannabis is a resource intensive-crop that requires equally intensive management. It may be a weed but to be its best, it needs a controlled environment.

A good mother plant is key

to producing a good crop. Seeds are not the way to go, says Zheng. Rather, he recommends using cuttings from a mother plant. The mother should also be replicated on a regular basis, lest it become too old. The new mother plants will be less

prone to disease, and yet the cuttings will still be true to the original.

The success of new plants and the yield they deliver depends on a host of environmental factors, just like any other crop. A key variable is light, as cannabis is photo-period sensitive and will only start to flower when light levels drop to 12 hours a day. Air circulation is important for limiting disease and pest pressure. “It’s simple, but if you want

to grow high-yield, high- quality plants, those are the things that you have to look into,” he says.

But the most important

variable, he told growers, is root zone management, which will affect everything from nutrient uptake to crop quality. “Integrated rootzone management – for plants’ growth, that’s really key,” he says.

An integrated (IRM)

approach means looking at more than just the growing media. It also means looking at the effect of canopy management on root development, and the impact water uptake via the roots has on bud development. Zheng cautions against cutting a plant’s leaves, as it could have negative effects on the rootzone and limit nutrient uptake. Conversely, putting less water into the rootzone will stress the plant during flowering, a stage when it needs water, causing it to produce more cannabinoids. He’s frequently asked what the best substrate is, and says there’s no right answer. “It’s really an integrated management [approach] to ensure the plant’s rootzone


has enough water, nutrients, oxygen, right temperature, [is] free of contaminants and pathogens,” he says. “If you don’t take the IRM approach, even if they gave you the most expensive substrates, you’re still going to kill your plants.” However, water quality is

important. The acidity of substrates also needs to be managed. Substrates with high pH were never a problem in the past, but pH has to be managed to ensure that nutrients are available to the plant. He prefers coconut coir

over peat because peat is naturally hydrophobic whereas coir will tend to hold water and make sure it remains available to the roots. Unfortunately, the biggest challenge growers face is grappling with the large number of beliefs around cannabis production. While myriad grow “bibles” exist to guide them, Zheng says few are grounded in scientific

research. “That’s why we’re doing the

research – to fill that gap,” he says. “People like to do different things. I still like to do research to find the sweet spot.” Many people use high-

pressure sodium (HPS) lights at the flowering stage, but Zheng says it’s a fixed- spectrum light. His experience with other crops made him wonder if a specific spectrum and intensity might be better suited for cannabis. “Do we know what plants

need for the different stages?” he asked.

LED lights can provide a range of spectrums and intensity, and Zheng’s work ultimately hit on red lights as the most energy-efficient for cannabis production, as well as the spectrum that delivered the best yields. (Ideally, growers aim for a gram of cannabis per watt of power.)

This is the sort of basic

research growers can undertake for themselves. Zheng encourages growers to start building the knowledge base they need for them to get up to speed in the fast- evolving sector.


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