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To Increase CBD Levels, You Might Just Need Male and Female Cannabis Plants

By Leo Bear-McGuinness

Published: Feb 28, 2019   
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It sounds strange. It sounds too human. But yes, cannabis plants have two sexes. Marijuana is from both Venus and Mars, as the old saying goes. 

Many people already have a vague idea that plants are hermaphrodites, and most are. Flowering plants produce both pollen and egg cells, while insects act as cupid couriers, bringing the 'sperm' of one flower to the ovum of another. 

But cannabis isn’t most plants. Along with the likes of ginkgo, willow, and kiwi, cannabis is one of the few species split into pollen- and bud-producing varieties, or in laymen terms, males and females. 

Of course, any cannabis grower worth their sativa knows this already. As the bud-producing sex, feminized plants are coveted for their THC and CBD, while pollen-producing males are regarded as worthless. 

But, with the right tinkering, male plant parts can have enormous value, too. In a recent experiment, researchers from the University of Connecticut induced female cannabis plants to produce male flowers. Alone, these plants still weren’t any more useful to a grower. But, when bred with other females, the results were spectacular.

“The benefit I have producing male flowers on a true female plant is that you know their type is XX, or that they just have the female chromosomes,” says Jessica Lubell, PhD, associate professor at the University of Connecticut’s department of plant sciences. 

“But crucially all pollen produced in those masculinized flowers is female. So, when you cross that plant with a true female, you will get all female seed and female plants, which are desirable in the medical industry because they have the most cannabinoids.”

Published in the American Society of Horticultural Science, Lubell’s paper demonstrates that, just by giving biology a careful nudge, growers can have a far greater control over the cannabinoid content of their plants – an ability that’s been talked about for years, but never proven. 

“So, in the online literature, the web forums and chats, the process of making feminized seed is out there, but there's really no published rates of using what's called silver thiosulfate to induce male flowers on a female,” says Lubell. 

The experiment worked like this. Rows of CBD-producing hemp plants were grown in a greenhouse and sprayed once every week for three weeks with silver thiosulfate, a solution commonly used in horticulture to block the action of ethylene, a plant hormone. Lubell and her team then counted the flowers, deduced their sex, and repeated for reliability. 

“By blocking the production of ethylene this somehow triggers the plant to continue flowering but not produce female flowers like it should,” says Lubell. 

“So, in the grey literature we figured out that the rate that's likely being used based on the recipes that are out there is a 0.3mM silver thiosulfate. So we tested that concentration, and we tested 3mM and had a zero treatment for control. In the end, we found that with the higher rate you get a greater masculinization, more flowers becoming male.”

From here on, an adept grower could breed these female/male plants with true females to create a second generation, highly potent in CBD and THC. The whole process could take as little as eight weeks, according to Lubell. But budding breeders be aware, an indoor garden is essential.  

“You'd want to make sure you have control of the environment, so that the mothers that are being pollinated don’t have any contaminating pollen,” says Lubell. 

“So an outdoor situation would be less than ideal because there is a lot of cannabis pollen in the air, just naturally.”

With the cannabis industry expanding rapidly and cultivators everywhere looking to maximize their cannabinoid levels, Lubell’s spray technique may have far more value than just a simple science experiment. If perfected and scaled up, it could help maximize plant production on a global scale. Although Lubell’s initial intentions were much humbler. 

“I did it almost as a convenience,” she says. “Because then [by removing the males] I wouldn't have twice as many plants to evaluate in a limited research space.” 

Out of convenience or not, the technique’s capabilities are enough to turn the head of any cultivator. But Lubell stresses that more research is needed before anyone rushes out to buy ten gallons of silver thiosulphate. 

“I'm only working with industrial hemp right now,” she says. “From the research that we do, I think medical growers can extrapolate and evaluate their strains and use this technique. But some strains may be more amenable to developing feminized seeds than others." 

“They may be better pollen producers. And once treated, they may succeed better.”

Leo Bear-McGuinness

Science Writer & Editor

Leo joined Analytical Cannabis in 2019. From research to regulations and analysis to agriculture, his writing covers all the need-to-know news for the cannabis industry. He holds a Bachelor's in Biology from Newcastle University and a Master's in Science Communication from the University of Edinburgh.


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