Stressing Cannabis for Stronger Plants & Higher Yields

by | Mar 18, 2020

Detroiter Karhlyle Fletcher is the host of High Lit, a cannabis research and classic literature podcast featuring leading voices and independent music. In addition to years in written and video cannabis journalism, he is also a traditional author.

The same way challenge provides athletes the opportunity for improvement, stressing cannabis plants is a critical step in developing healthy harvests. Nothing gets better without practice. Plants are the same way, and while other agricultural industries are well aware of how to push their crops, cannabis still has more to find out. 

Stressing Cannabis Makes It Healthier? 

Several grow operations, including Medpharm out of Colorado, and Cresco Labs out of Illinois, purposefully use stress to encourage growth in their plants. “While no formal studies have been completed,” master grower for Cresco Labs Jason Nelsen said in an interview with Massroots. “Heat and drought stress [in cannabis plants] can increase resin production as long as the stress is not excessive in nature.”

Cannabis Tech enjoyed the privilege of talking with Fluence’s David Hawley, Ph.D. Fluence is a lighting company headquartered in Austin, Texas. This company provided LED lights for 1.7 million square feet of cannabis canopy in 2019 and manufactures its lights in Austin, Texas, Kunshan, China, and Monterrey, Mexico. Through investing a high amount into research, and actively offering quality support for their machinery, Fluence is a leading brand in the world of cannabis lighting. 

When asked about purposefully stressing plants, Dr. Hawley said, “The idiom that I know of that’s related to that is ‘calm seas don’t make the sailor.’ You have to be faced with some challenges in life to improve, and that analogy certainly fits here. In the context of indoor agriculture, whether we’re talking about the cannabis industry or a basil grower, that’s absolutely a strategy to use.

You can do this by “stressing” the plants, whether with light, intermittent drought stress and strategic irrigation strategies, or working with a living substrate strategically to make an optimized plant. The more you learn about one of these strategies, the more you can implement all of them and get the plant that you’re after.”

Stressing Cannabis With Light 

Every plant reacts to light in a myriad of ways. As complex as sunlight is for human health, it’s similarly impactful on plants, if not even more complicated. Stressing cannabis appropriately at the right time can be challenging to figure out, but it’s straightforward to understand. 

“There are lighting strategies you can use to induce something called Systemic Acquired Response,” Dr. Hawley explained. “You can think of it like how we get a flu shot. When you get a flu shot, you get inoculated with a little influenza virus, but it’s such a low concentration that your body can recognize it and say ‘hey this isn’t good’. Then your immune system can learn how to combat it, so if you’re exposed to a higher concentration of this virus, your body already knows how to defend itself.

This is something you can do with plants by using UV-B light. It’s a higher energy photon as compared to visible light, but it’s not nearly as dangerous as UV-C. With UV-B, what you’re doing is not necessarily just surface sterilization, although you are doing that as well. What you can do in some cases though is if the plants are routinely exposed to UV-B in strategic doses, it’s similar to boosting the plant’s immune system. The plant will up-regulate certain compounds, secondary metabolites, that in general make a plant more resistant to biotic and abiotic stresses; by strategically utilizing something mildly stressful like UV-B, you can have a heartier crop.” 

By stressing cannabis through hostile environmental factors, the plant becomes stronger. Such development impacts the compounds within the plant in different ways.  

stressing cannabis

Does Stressing Cannabis via Lighting Affect Flavonoids? 

Flavonoids are usually associated to some degree with pigmentation,” Dr. Hawley stated. “If you think about what UV does to our skin, you go outside, get exposed to UV, and get a suntan, that’s our skin trying to defend us against high energy light. Plants do the same thing with flavonoids.

To provide a few examples, if you’re a connoisseur of red wine, the titular red pigment is a kind of flavonoid. Similarly, flavonoids can be found at the grocery store if you ever buy red-leaf lettuce. That lettuce could be much redder if it were grown under a high energy light, like blue, or even some UV-A, for instance, because the plant is giving itself a [sun]tan to defend against that light.

There’s more to this broad family of compounds than just causing pigmentation; articles and book chapters have been written on just this class of compounds about the healthful effects they can have on the human body. The short version is, that many flavonoids are very useful to the plants that produce them and the people that consume them, so for us to be able to increase concentrations of flavonoids in plants with light is a beneficial technology.”

Due to flavonoids’ role in protecting plants from external stressors such as the sun, it seems apparent that lighting stress would impact their expression. Manipulatable LED lights are the best option for managing this sort of stress. By changing the color of the light, cultivators control the flavonoid expressions of harvests. Lighting recipes lean into this scientific reality. 

How Does Lighting Stress Affect Cannabinoids? 

“As for cannabinoids, there is a lot of conversation and speculation about regulating cannabinoids through UV light. There’s only one formalized study I’ve seen. It’s by someone named John Lydon from 1987. It’s a well-executed study where they used doses of UV light in the middle of the photoperiod, so right when they speculated would be the brightest part of the day in the natural environment the plants had evolved in, they applied doses of UV-B light.

They found in their study that it dramatically up-regulated THC concentrations. No one has recently executed a follow-up study on this. At least, based on that study, you could hypothetically up-regulate THC by using UV light, but I wouldn’t say that’s conclusive right now.”

How Does Stressing Cannabis Affect Terpenes? 

“As for terpenes, I’d say terpenes are the hardest to comment on because terpenes generally aren’t implicated in abiotic plant defense mechanisms, they’re more for aromatic and biotic stresses. In other words, pathogens, like little bugs eating the plants and so on. Terpenes could be a deterrent for those, but they’re not so involved in protecting against environmental stresses. Different light qualities do seem to modulate terpene profiles in cannabis based on research we have conducted and have ongoing, so perhaps this is a stress response after all.”

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