Episode 165: Boosting Yields 50% with a 13-Hour Photoperiod? Debunking Cannabis Science with Dr. Youbin Zheng

Welcome to the Cannabis Cultivation and Science Podcast. I'm your host, Tad Hussey of KISS Organics. This is the podcast where we discuss the cutting edge of growing from a science-based perspective and draw on top experts from around the industry to share their wisdom and knowledge. My guest this week is Dr. Yuben Zhang. Dr. Zhang is a professor at the University of Guelph in Ontario, Canada, where his lab has been at the forefront of high THC cannabis research since the country legalized recreational use in 2018. As a principal investigator, he collaborates directly with licensed commercial facilities to ensure his lab's research can be applied by growers right away. He is also the author of the recently published Handbook of Cannabis Production in Controlled Environments, a definitive scientific resource for students and cultivators alike. Alike. Dr. Zhang and his team of talented graduate students and research associates look closely at all aspects of indoor and greenhouse horticulture management, ranging from light intensity and spectrum to deficit irrigation and proper crop nutrition. His breakthrough findings on extended photoperiods, UV radiation, and phosphorus thresholds are actively changing the way cultivators optimize their facilities and manage plant health. Joining us today to talk about how a 13-hour day cycle can radically increase flower yield, the realities of utilizing drought stress in late flower, and and why the industry is vastly overapplying phosphorus is Dr. Yubin Zhang. Now on to the show. Dr. Zhang, thank you so much for coming on the podcast today.

Thank you for having me.

Yeah, I was fortunate enough to hear you speak at Photo X. I think I've actually heard you speak there a couple of times now and you shared some of your research around photobiology and I'd love to talk to you about that. But can you share a little bit about yourself and your lab?

Sure, yeah, it's always fun to go to the Photo X and you got all the experts over there, people like you, very enthusiastic about cannabis cultivation. So it's always very enjoyable to be there. Well, I'm a professor at the University of Guelph in Canada. For people don't know where Guelph is, we are in southwest of Ontario in Canada. Legalized for cannabis recreational use in 2018. It's the first developed country legalized for that. So we are fortunate enough in this location. So we can do lots of research related to cannabis cultivation, especially high THC cannabis cultivation. But of course we started doing research even before that. So yeah, my lab is at the University of Guelph. And we, at the beginning, we conducted loads of research with licensed growers at their site, either in greenhouses or indoor. Cultivation facilities because they have all the securities and then also license. And another thing is that I like to do research that can be used by growers right away. So that's another reason we done lots of research with the growers. So you probably, you and your audience probably saw lots of our publications. Majority of our publications are from research conducted from at these facilities. Of course, while we are doing this research, we always already communicated our results to them so they can apply the result directly to their operations. At the University of Guelph, we also have research facility. We can do cannabis research. So myself as the PI, and then also I have a few research associates here and loads of very talented graduate students, master's degree students. And PhD students worked with me on cannabis cultivations. So that's, I guess, I'll stop here about me.

Yeah, I got to connect with Dr. Kaplan the other day in Minnesota. That was really fun. I know he came out of your program. I wanted to dive into the research, but I, I, as you were saying this, I did have a question pop up. Do you, did you see a difference between researching high THC plants versus hemp in terms of how that research can be applied? Like, Do you, do you think there's a, like, can we use the research on hemp and, and apply it to our, to high THC cannabis, for instance?

Yeah, that's a very interesting question because I haven't seen anybody put it side by side to compare. And, but I do know that cannabis have such a big genetic differences. Even for high THC cannabis, um, you, you look at cultivation, you look at photoperiod, and different cultivars will respond very differently. So, as you know that THC, high THC cannabis, been the focus for many people, especially the legacy world. Um, You know, people done so many crossing, so many breeding in the past, and there are so many different genetics. They are so different from hemp. And, you know, we also even know that high THC genetics now we are using are very different from 1970s, 1980s. Yeah. Um, you know, even you look at THC, now you are looking at more than 30% THC content, but even in the 1980s, a few percent THC content. Yeah, it's, uh, it's difficult to, to, to say, but of course, I guess certain things it's similar, but there are lots of things can be different.

So would you agree that, that maybe because of the genetic diversity in cannabis, just as a plant being so wide and so diverse, that any research findings should be viewed somewhat critically through a, through a lens and just realize that because of this genetic diversity, not everything can be applied maybe quite as literally, or maybe, maybe we need to do more individual research as growers. Before just making an assumption based on research?

That's a very good point. That's what I always encourage people to do. For example, in the past, people believe and all everybody knows that cannabis is a short-day plant. They need 12 hours to induce flower. So majority of the commercial cannabis producers or cultivators have been doing that, which is fine. But our research, we found that some of the cannabis genetics or cultivars can even flower under 15 hours photoperiod. And some of them really they need 12 hours dark, uninterrupted dark period. So to answer you for that question is that even, you know, for high THC cannabis, the genetic differences, different genetics response to the environment and management, horticulture management strategies can be different. So in a way is that, you know, we done research and we know some of the cultivars, they can flower even you gave them shorter than 12 hours uninterrupted dark period. That means they can have longer photoperiod to have more light so they can produce a higher yield. But having said that, our research is just say there is a possibility. We demonstrated that. But for growers, because they have different cultivar, have different genetics, and again, some of them may do well, some may be not gonna do well. So the best thing is to do some trial in their facility. And then I know different cultivators may have the facility to do, they may not. Have the facility to do certain things. If they are not be able to do that, they can collaborate with research institute to help them to do that. But if they want to do by themselves, and we certainly can help them to design the research, not to the, do the research as we do here with all the treatment, but we can design some research design much simpler to achieve what they can achieve. By the way, in Canada, if you are working with research institutions like university, us, and some other publicly funded research institute, quite often if you put some cash on the table, we can use that money to leverage from, to get much more money from the government to do research for you. But then the good thing is that while we are doing research, we communicate all the results directly to you. And then also because it's conducted in your facility with your genetics, you can use it right away. After we publish our results 1 or 2 years later, you'll be able to see it. But not necessarily they can directly use our result. They have to, it's just the principle we can give to them, to the growers to guide them. If the research is not done in their facility, we don't, normally we don't do research repeatedly doing the same thing. We just want to help the cannabis industry. To move forward. That's why we do research, quite new, you know, light intensity, photoperiod, filigation, all aspects of productions. But simply to answer your question is that people do need to try their own for their own genetics and growing environment for certain research results coming out from research institutes.

Yeah, you mentioned, uh, photoperiod specifically, and that you, you know, some of your research has shown that these high-TH cultivars can perform quite well at, say, a 13-hour day cycle or photoperiod, which gives you 8.3% more light energy, or your DLI increases. And there's a lot of research that even that you've done that shows that increasing light intensity or the amount of light a plant gets during that daylight period will increase yield proportionally. So I guess my question is, is there— do you feel like this is pretty— is that 13-hour photoperiod is pretty safe for most genetics, or are we risking, you know, hermaphrodism with, uh, a lot of what's commercially being produced right now?

Well, again, I would say there is a possibility that some cultivar wouldn't work, some cultivar will work. If people are interested interested in, they can go and read our two published papers. And both papers are by one of my previous graduate students, Ashni Arun, Erickson, and my research associate, David Lewallen. If you go to Google Scholar and just put my name plus cannabis plus photoperiod, you should be able to find these two papers for free. The first paper we did was, you know, we used 10 different cultivars. Some of them flowered under 15 hours photoperiod. Some of them really need 12 hours uninterrupted dark period. But having said that, even if the cultivar flowered under longer photoperiod, They are not necessarily going to give you the yield. That means the flower not necessarily going to be big enough. And so it's only some cultivars that under the longer photo period, the, the flower, the bud can really grow well and compacted flower and a good yield. So we selected two. Cultivars from these 10, and then we grow them under 12 hours, and then this is under 13 hours. As you mentioned, it's only a little bit more than 8% of more light, but we got yield-wise, one cultivar is more than 39%. The yield increased 39%, and then the another one yield increased 50%. This was— we didn't hypothesis that, we didn't think, we just know that more light linearly, the yield will linearly increase. But we didn't know that just increase that photoperiod 8% of that, you increase that much yield. And then also from our research and other people's research is demonstrated that the light intensity If the light intensity is higher than certain level, if you increase light intensity, the cannabinoid doesn't increase. Cannabinoid content doesn't increase. However, when we gave 13 hours photoperiod versus the 12, THC increased 9%. Huh, it's wild. It's just You know, even for us, it's a surprise. But then you done it, you know the research was well designed, got enough replicates. That's the data over there. So yeah, people interested in, they can go and have a look to find out more detail.

Has anyone attempted to replicate this research that you've seen?

I haven't seen any. Publication directly repeat ours, but there are some research looking at longer photoperiod published, and then also see certain cultivars yield increase. And then also commercial cultivators, I saw their result. Of course, most of them don't like to publish, but I sometimes do have access because I They trust me and then I keep their secret. But I see, I saw similar result. But of course, again, it's cultivar dependent.

Sure. So you're, you kept light levels the same across the two treatments and you had two cultivars, one at 12 hours. Well, both, both cultivars you ran at 12 hours and you ran them concurrently at 13 hours and you got a 39% increase in yield and a 50% increase in yield. That is crazy. And did you see a difference in like flower morphology or bud maturity or anything like that in terms of how the plants looked?

The, um, flower density under the longer photoperiod is a little bit reduced by comparing to the 12 hours.

But you also got an increase. Of THC, you said, too.

Yeah, that's right. Yeah.

Other secondary metabolites? Did you also look at terpenes or other cannabinoids beyond THC?

We didn't look at terpenes, but other cannabinoids, because this is high THC, and so we've been focusing on THC. But we reported, if you go to the paper, you can see, some other cannabinoids, CBD and CBG changes over there as well.

That's really interesting. I will link to those papers too on the podcast page for people who are interested. All right, well, we talked a little bit about light intensity. I'd be curious to see how those plants performed if you gave them the same DLI. I can't imagine you would get the same yield or, or, uh, THC increase. Have you looked at that at all?

That's another research to do. See, there are so many things we don't know about cannabis. We, like in our writing, we did speculating that, um, you know, that's the next step to do. And then also you can play around the photoperiod and as well. The reason we didn't do that. Give them the same DLI, just longer photo period, is that we don't feel that's need to be done. If you're a scientist, just curious to see what's going to happen, sure, go for it. But for cultivators, because at this moment we just want to do more and more research so the cultivators can use it. Because our previous research already demonstrated if you increase light intensity from about 200 micromoles to 1,800 micromoles, the yield linearly increases. Therefore, if I can increase photoperiod, I wouldn't reduce my PPFD for that because you just keep your lights on. For one more hours, you can have higher yield and higher THC. Why should I crank it down? That's why we, we are not going to do that. But you can do that as a scientist, just for curiosity.

I was thinking of it the other way, as terms of cranking it up versus on the 12-hour versus cranking it down on the 13-hour. But I, I, you make a very good point there. Let's, let's talk about that because you published data that shows this linear increase in yield and in fluorescence. Up to 1,800 micromoles, which is a lot of light.

Yeah.

I don't know any commercial facilities that are running that high, and maybe they exist, I just haven't worked with them. Being an organic guy myself, I don't know that we can push plants to 1,800. I'm not sure. That's a great question. Can you talk a little bit about what that linear relationship is and what that, what those findings are?

Yeah, sure. So we grow cannabis in a commercial cultivator's facility. So we grow the plants within the same environment, but provide each plant with different light intensity. So there were many, many plants. They all under different light intensity. It's randomly allocated to them. And then we grow the plants for about 9 weeks for short-day plants, but anyway, probably the best is to provide them source of that paper. That paper is written by Victoria Rodriguez Morrison and my research associate David Llewellyn. And then again, if you search for Nightingale Intensity Cannabis plus my name at Google Scholar, you should be able to get that. So If you look at that, the plants were actually grow— some of the plants were growing under 90 micromoles all the way to 1,800. And then so we harvested the plants and then weighed the yield of each plant. And then the yield is linearly increasing. The reason we want to do that is that, well, outside at lunchtime in Southwest Ontario, you could get in average about 2,000 micromoles of light. But of course, outside is not always on, the sun is not always there, but indoor you can have the light on high all the time. But we just want to know Well, what is the best light level for growing cannabis? That's why we did that research growing the plants. And so we found that there was a linear regression. And I do understand Fluence and Dr. Dave Erickson's lab. They also used their different cultivars under different environment. They grow plants even over 1900 micromoles. They got similar results as we got. Yeah, in a way is that probably 1800 is too high. But again, is that we do research, just want to demonstrate to the cultivators The more light you provide to your plant, the higher yield you're going to get. It's linear. But whether you're going to use that high or not, it depends on loads of things. You know, the highest light level gives you the highest yield, but does that translate into you profit the highest, or can you system handle it. These all need more research to figure it out. That's again, we do research just to provide some insight for cultivators, and then they can figure out based on our research from there.

The, the general statement I heard was that, and again, this is a little approximate, but approximately 1% more light will equal 1% more yield. That was sort of the term I heard thrown around at Photo X a lot. Would you agree with that in terms of this linear relationship, or do you feel like it's more nuanced?

I wouldn't use that all the time on all the crop because if you grow lettuce, 1% increase of light, the yield is the whole plant tissue. If you grow cannabis, it's only the flower is the yield.

Sure.

So in a way is that, of course, we are able to, if I go back to that paper, we should be able to figure out what's increase 1%, how many percent increase for the yield based on our paper. We are able to figure that out. But I haven't done that. But anybody can go and just look at that paper. Just say under that condition. We did that even the CO2 was not enriched. Just keep that in mind. If you get CO2 enriched.

Oh, you weren't enriching with CO2.

That's right.

Just ambient levels.

Okay. You get even higher. Increase.

Yeah, we, the analogy one of my colleagues likes to use is when you reach those higher light levels, it's like driving a supercar. You have to have the right gasoline and the tires and everything, cuz you are much more likely to get in an accident going 200 miles an hour down the road versus driving at 60, which would be like maybe 800 micromoles sort of an equivalent. So there's just a lot more ways for you to screw things up when you start pushing the plant so hard at those light levels.

Right or wrong, could be. You know, if we look at that, you know, if you drive at 60 and your fuel efficiency is much higher.

Yes.

That you drive 100. But between 200 micromoles to 1,800 micromoles, as we did, it's linear. That means the efficiency, it's the same. Hmm. So, and then also, if I have a facility, I have to spend money to build that facility. I have to hire people to do it regardless. But just by increasing light intensity, I can have increased yield. Without changing anything else.

You're saying all other variables the same, just increasing the light.

Yeah, roughly I remember from that curve, that linear regression. What if I increase the light intensity from 500 to 1,000? I could roughly get doubled the yield. So double light, double yield. Would you do that or not? Absolutely. So in a way, yeah, it's like driving, but in a way it's maybe not. If the light response curve already start to curve, it's not in the linear part, the efficiency is decreasing. It's just like you drive 100 miles, your fuel efficiency decreases. But when you are within that linear portion, your efficiency Still high.

Stays the same. That makes sense. Did you look at, or did you see at 1,800 micromoles, did you see a photo bleaching? Because I know that that was a hot topic at PhotoX this year.

No direct correlation there.

Were the lights that you were using high in, in red light, that red spectrum?

We, we used red and blue, but I cannot remember exactly what's the ratio. Again, in that paper, you should be able to Okay. Yeah.

Wonderful.

Yeah.

Well, since we're talking about lighting right now, you've also done research on supplemental UV radiation, UVA and UVB. There's this industry belief that UV may increase secondary metabolite production like THC. What was your findings from your research on UV specifically?

Not increased, but decreased when you increase UV. So we did, um, at least 2 trials, and the first one was done by Victoria and David. And again, if you search, you will be able to find it. The second one was by David. The first one, we just used UVB, and the last 3.5 hours, during each day. And then the range of UVB was from zero to high enough. And for Dave Erickson's research, we used UVB alone and UVA plus UVB. And not a single one we saw any cannabinoids increase, only decreased. The early common belief, I would like to think it is from the paper published in 1987. They did a research looking at exposing cannabis to UVB in a greenhouse. And there was a linear increase when the UVB dose increased. The THC in the flower and in the leaf both increased linearly. And our research, the dose of UVB covered their range. And so we didn't miss anything. But why so different is, we don't know. But I, if you need me to speculate, is that probably in the '80s, that paper, that trial, the cannabis they used, the THC content was about 3%. Ours, I cannot remember, it's more than 25%. And so if you want me to speculate, UV is a stressor. And so when the THC content, cannabinoid content is low. If you stress plants, probably you could get a little bit increase, but the high THC genetics nowadays already have very high THC content. So we didn't see any increase. Rather, we, we, you know, Victoria, Victoria's research, we use two cultivars and both of them with THC, CBD increased with the increase of UVB dose.

Decreased.

Decreased.

Yes. They decreased with the—

okay. Yeah, both decreased. And then just one cultivar decreased more. The slope was steeper and another was not as steep, but it's all decreased. And terpene decreased as well. David's research did find that UVA and UVB, that treatment, increased the THC content slightly in the sugar leaf, not in the flower. But again, the sugar leaf, the THC content was 0.3%. So under UV, there was slight increase. So overall, we didn't see it's, see any increase, but we did see yield decrease. The higher UV, you got lower yield. The plants were smaller. One good thing is that It does, it did control powdery mildew.

So you saw a reduction in pathogen load on the plants from—

That's right. That, that was not part of the experimental design, but both trials, we did see if you have high UVB, and then you don't see powdery mildew on the plants. Without UV, you can obviously see the powdery mildew on some of the plants. But again, is that, why should I use UV to control powdery mildew? And then again, is that you have to try to find out the dose that probably will reduce powdery mildew, but without affecting your yield and without reducing the cannabinoids content.

Well, I would think that those photons, those UVB photons would have to hit the powdery mildew spores or conidia directly in order to have any impact, unless they're causing the plant to produce some sort of systemic response, some sort of SAR response. And a lot of, as I'm saying this, I think a lot of powdery mildew usually occurs in more humid and microclimates inside the canopy. So I would think those areas that are most persistent with powdery mildew would not be treated by UVB. UVB light unless it does create the SAR response. I don't know. What do you think about that?

Well, that, that certainly needs more research, but not that much research done looking at UV on cannabis, but there are lots of research looking at UV effects on other plants. Because in the past, when global climate change was not that hot yet, There was ozone hole and then all blocking UV. So lots of research look at the UV from the sky, how do they affect plants. So everything you mentioned, they are probably, you are able to dig into that in the literature. But for cannabis indoor production, in greenhouse production, how to use UV for pathogen control, Certainly there are more work need to be done for sure.

So just, just to recap, there was research done in the '90s that showed that UVB increased THC content, but the plants that they used had very low THC levels. Like you think you said roughly 3%. You redid this experiment, uh, and it was done in a greenhouse and you redid it indoors. So no. Natural light and found a decrease in yield and THC production. So sort of the opposite result. Is that, just to summarize, does that sound pretty accurate for the comparison of the two?

Sure.

Yeah. And then do you think that the fact that the greenhouse trial was done with natural light, that somehow that sunlight spectrum or light intensity could have played a role in those differences in results?

Could, could, but I don't know. Because in greenhouse you could, because it depends on the, the material of the greenhouse. Glass and poly may block UV differently. And then also when plants previously exposed to UV, they would respond differently. So there are so many things, uh, don't know. Um, but, um, the research we done use different cultivars, different environment, all under LED lights.

That's, I mean, that's, that's one of the things I love about the cannabis plant as a crop is there is so much research still left to be done and so many unanswered questions. So I appreciate that.

That's why we still working on it. Yes. So, uh, yeah, excited and also fascinating. So we always have some research going on, digging into more for the industry to improve their operations.

Yeah. Now, before we switch off of light specifically, is there any other interesting, like, research or myths or things that you would like to touch on regarding light itself before we move to another topic?

So one thing I found that some people don't understand is that they use light response curve from a single leaf, or even just put a plant in a growth chamber to do a light response curve, and then use the light saturation point from there to guide their cultivation. This is wrong because single leaf doesn't respond similarly as the whole plant. And most importantly is that plants acclimate to the lighting environment they've been exposed to. Say if you grow a plant under lower light and then you take that plant in a growth chamber or whatever to do a light response curve versus you do a light response curve by growing a plant in a high light environment and then take it into a growth chamber to do the light response curve, you will get two different light response curves. So the only way to find out how to do a light response curve so you know how your plant responds to that is to grow your plants from the beginning to the end until you harvest under different light environment. That's the only way. To do it.

So, so what you're saying is for a grower to take a particular cultivar, whatever genetics it is, and find out what its capacity is for light and yield, you would need to grow it under different treatments. So you can't start a plant at, say, 200 micromoles and then throw it under a much higher level of light rapidly. We need to, we need to grow plants if I'm hearing you correctly, at different light levels initially in order to really understand or maximize what that plant response might actually be throughout its flowering cycle?

No, it's more how do you decide what's the— how do your plants respond to light intensity. It's just like how we did our light response curve by growing plants under different light levels for their whole life. Yeah.

Okay.

So you have plants here grow under lower light, plants here grow under higher light, but grow. So you have to do it by growing them from the beginning to the end, harvest the yield and plot the yield against your light intensity.

So you're saying you have to keep the light levels the same throughout the entire life of the plant to really get a good idea of what that response curve is.

Yeah.

Okay. Okay.

Because in the academic world, many people do take a leaf and put in a cuvette to change the light intensity from low to high to get a light response curve. This, you can do that to see the plant physiological response, but you cannot use that light saturation point to guide your cultivation. Say beyond that, the plant doesn't respond.

I see. So we, we can't make decisions based off of these light levels. Okay. Interesting. Because, because actually what your findings are is these plants can handle a lot more light than that research would demonstrate.

That's right, because plants, their lighting history, because plants, if you put any plants under any light environment, they will adapt. The morphology of that leaf and then biochemistry of that leaf can change. Many people probably have these experiences that in the spring when you go buy bedding plants for your garden, if you buy and then right away you put plant them outside, they will get sunburned because these plants were growing under greenhouse, under lower light. Plant them outside right away, they get sunburned. And, but then if you slowly move them out, they take just a few days to adapt. Their morphology, their biochemistry can be adapted. So if you want to do a light response curve, you have to grow the plant under different light environment.

So from a grower perspective then, how would you recommend that transition from, you know, veg to flower? Should we be starting with our lights lower? Should we be targeting DLI? What's the best way to make that transition for plant health, in your opinion?

Transition is normally the, um, I can talk to you about this for another hour. Is because during the vegetative stage, you know, depends on how long your vegetative stage you want it to be. And it also depends on the cultivar. If your genetics is compacted, then you don't want to use high light intensity because it will become more compacted. And you want to use lower light intensity to get your plants stretched a little bit. But of course you can use different light spectrum for doing that. We can talk about that because when I teach my students, that's about half an hour. And then you move your plants to flowering, for flowering stage, and then The flowering stage, as we already mentioned, that the more light, the better yield. So normally, so the flowering stage probably have a higher light intensity. If your plants from vegetative stage, if they were growing under too low a light intensity, don't right away bring them back. You, you can bring them here, but because the LED, you can dim it. Don't give them full blast right away, you know.

So, so let's say I was, I had plants in the vegetative state under, let's just say 600 micromoles, 600 PPFD, and then I, I'm going to flip those to flower. What, could I go to 800 right off the bat, or would I want to keep it at 600 for 24 hours, or what, what kind of like SOP would you recommend around that transition? Let's say I was targeting 1,200 as my final light intensity level. How would I get from 600 to 1,200?

Well, if you, if you do 600 vegetative stage, what you could do is before you move to flowering stage, you could just increase your light intensity, especially if you have an LED. Say 100, give or take, 100 micromoles every 1 or 2 days. And then gradually you can move to 800. But give your plants a few days to gradually adapt to that rather than right away to give it. But I would like to think probably from 600 to vegetative stage right away to 800 micromoles flowering stage should be fine because one thing is that the flowering stage, the photoperiod is much lower. And then 200 micromoles from this stage, 600 to 800, I don't see any issue over there. But if the gap is too big, you may have that issue. You may get plants stressed, but it's always better not to get them stressed too much.

In translation, there's a lot of hormonal changes happening to the plants at that stage, so we don't want to be giving them a lot of additional stress. Stress is interesting, and maybe this is a good transition to talk about drought stress, but in general, stress will increase— and correct me if you disagree with anything I say here— stress will increase secondary metabolite production, but typically at a cost of yield cost. As a grower, there is this sort of dance or relationship we're always doing between yield and secondary metabolite production. You've done research on controlled deficit irrigation, so drought stress in the late flowering stage. Do you want to talk a little bit about that, those trials, and what your results were?

Sure. And then you are absolutely correct though, you know, any plants under stress, they will produce more secondary metabolites than certain But, you know, it's how much more, and then also whether you're going to reduce the yield or not. And then that all depends on the type of stress and how much you stress it. So we did that, the drought stress, as you mentioned. That was done by probably North Americans first. Cannabis Cultivation PhD, my student, uh, Darren Kaplan. So that was one of his chapter. So we grow plants normally, and during the short day period, day 39, and then we hold the water without giving the plants water, and then they control still regularly watered, but for the drought stress, we just hold the water without giving to the plant until the plant's leaf starts to show wilting. So you see the sign of wilting and then you start to give plants water normally. So that's a stress. And then you have, we harvested the plants, THC, CBD content, that those are the the concentration. One increased 12%, another increased 13%. And then we also harvested the flowers, so there is yield. So the, the biomass of the flower times the concentration, you got the yield of THC and CBD. That's increased about 40%, I cannot remember exactly. Again, if you type my name, drought stress cannabis, you'll get that paper. Then I will show you. And then so you see here is that you stress the plants, secondary metabolites increased, yield also increased. Because normally when you say yield will decrease, it depends on what you treat as yield. In our case, it's the flower. So it's the reproductive organ. So plants under stress will produce higher secondary metabolites, but at the same time they want to produce more offspring to survive, so they will produce more flower. So that's the mechanism you can look into. This is very interesting actually. So we were growing plants in an 11-liter pot. We only stressed the plants once, and it worked. Of course, when Darian and I go and talk to the growers, and we, after we published, many growers, commercial growers, been using this technology. When we talk to people, they say, yeah, we've been using it, we've been using it, because it's so easy to use. You even don't need any instrument. You just see the plants showing wilting, and then you water them normally, your plant's guaranteed already under stress. Because even before the plants need fueling, wilting for cannabis, there are loads of things happened biochemically, happened in the plant hormonally. So of course we were excited. And, and then we designed another trial. We say, well, you just drought stress the plant once. You can't get that, such boost for cannabinoids and yield. How about we stress them many times? So we said, okay, we'll stress them at different times. And if you want to stress them at different times, and then the pot has to be smaller. So the first one we did was in an 11-liter pot, so it's big. And then we want to stress them more frequent, so we grow them in a 6-liter pot. And then the result is that there was no increase of cannabinoids of the drought stress, regardless of how many times you stress them, comparing with the control. That's why You know, we, we said, how come? So we even didn't get a chance to publish that part, but that part is in Darren's thesis.

So the control was the one-time drought stress or the control was no drought stress?

No, the control is not stressed.

No stress. Okay.

Do you know why?

Why?

11 pot, 11-liter pot, 6-liter pot. So the plants may be already stressed by the size of the pot.

So you had to introduce another variable because you needed the plants to dry down faster so you could do the induced drought stress, but you're also introducing another variable that creates a little bit more I guess noise in the data.

Yeah, but having said that, in the 16-liter pot, smaller one, no drought stress versus all these plants get stressed, there was no difference between these plants and this control. However, however, if you compare the cannabinoids, THC, CBD content, of this control to the first trial on the just stressed ones, the THC/CBD content were very similar or even a little bit higher for the smaller pot.

So if I'm understanding correctly, and this is all, this is using mineral salts, just to make sure that everyone understands that. Your results were in a 6-liter pot, it produced the same or better yields and secondary metabolite production as the 11-liter pot with one drought stress event that had that 12 to 13% increase. So just by introducing, do we call it root stress by root restriction stress? I don't know what the terminology is on that. You were able to get the same secondary metabolite and yield response.

Yeah.

That's really fascinating.

Yeah.

I mean, I'm an organic grower, so we can't utilize these things exactly the same way.

No, you can. That was done using organic production system.

Can you explain that? I'm really curious.

That was organic fertilizer, Dan Trail.

The 6-liter.

Or both. If you go dig out the published paper, it's, we used organic production.

A liquid fertilizer? Um, Oh, I, I have, I have an interview with Dr. Kaplan coming up where we're going to talk specifically about this paper because I think it's so fascinating and one of the first examples of really this crop steering, you know, that buzzword that we're hearing around cannabis now.

Yeah.

It's really the first research I've seen on sort of crop steering with cannabis induced intentional stress.

For sure. There are loads of things you can do to steer the plants. But anyway, just coming back to that is that it's organically grown. One thing though is that you don't see any publication talking about these two comparisons because they are not done the same time. You know, if you want to prove it, you do it the same time. The conclusion though, I would like to speculate is that yes, you can use stress. Root zone stress either by water or by the size of the root size to stress if you know how, but not, don't overdo it because eventually if you overdo it, your plants will grow slower, smaller, and then also have yield reduction.

I think that's a really good point. And I think that's the tricky part for a lot of cultivators, especially commercial cultivators, because in a, someone who's visited a lot of facilities, facilities like I'm sure you have, there's a lot of unintended plant stress that just occurs in a facility. And my concern would be if we do intentional stress on top of the unintended stress that's happening either through improper fertigation or microclimates or environment or, you know, poor irrigation practices or poor pruning practices, you know, all of these things that can occur, could we be leaving yield on the table or sacrificing yield by overstressing the plant?

Well, you could, but then one rule of thumb is don't stress your plants too much in the early stage.

Yes.

You know, our another research looking at yield response to nutrient or fertilization, it's just demonstrated very nicely that the larger the size of the plants, especially the roots, the larger they the yield. So in a way is you grow your plants nicely, only stress it at the late stage. And so at that time, plants will invest more in the reproductive portion.

So we want to keep our plants really healthy, especially through that, what people call that stretch period of growth where the plant's really increasing in height. And then as we get to the last 2 weeks, last 3 weeks, that's when we can sort of intentionally stress the plant to increase inflorescence production or bud flower production. That, that makes a ton of sense.

Yeah.

I think people have used Dr. Kaplan's research and maybe, well, first of all, I think it's fascinating and really interesting. I think it's been misapplied by some people, and I think that's where I really want to talk to him and get into some of the nuance of his research and what he thinks we can really apply it to and what maybe is overgeneralization of what this all means. So. But just so I understand, you're saying that you found an increase in yield in the smaller pot in organics, because that would go directly against what my understanding is. And then what you just said, where by increasing root space, a larger container, we get a healthier plant, we get larger yields in general. This research showed the opposite.

Uh, I wouldn't say it's showing opposite. I just saying that your plants already stressed, but not stressed enough to reduce the yield. Only stressed enough to trigger the plants to shift more their resource into reproductive, which in this case is flower.

So the plant has this limited amount of resources. And we can somewhat manipulate where it puts its energy. Yeah. Whether that's biomass production. And again, like you said, all we really care about in the case of high THC cannabis is the flower itself. So we can kind of control whether that energy goes into secondary metabolite production or into biomass production or plant defense because it's stressed due to herbivory or pathogens or other issues, which also can reduce yield but increase secondary metabolite production.

Yeah. Yeah.

I, uh, my favorite example is this is, and a lot of growers can relate to it, is where you have that plant that's growing on your compost pile that got chucked out and somehow it just managed to survive. And it's the ugliest, poorest yielding plant ever. But the, the cannabis that it grows, it ends up producing, well, people always say it's the best because it was so stressed that it created like all these secondary metabolites. but it wasn't able to put that energy into yield or any of these other things. So it, I don't know, it's a kind of a fun example that I hear from people.

Yeah, there, there is a balance for sure. There is a balance. As I said already, is that you have to grow your plants to certain size and then they would have the carbohydrate, everything. And when you stress it, that's the resource is already there and then it can turn into second metabolite. But if your plants get stressed more, they are just surviving, sure, probably you'll get secondary metabolites very high, but you don't want to go there unless the cannabis industry develops into the stage as our wine industry. People just want that.

Yeah. Yeah.

Otherwise you don't make your ends meet.

That makes sense. All right, so last question, cuz I know we've been talking for a while now, but I wanted to just touch on this, this phosphorus topic because it's something that I think is really interesting. So a lot of the, the industry standard puts us around, let's say 200 milligrams per liter of, for phosphorus, PPM of phosphorus. But your research shows that maybe what the plant actually needs or what that sweet spot is, is significantly lower than that. Can you just touch on that really quick?

Sure. And then again, that you can search on internet to find our paper. And so we use phosphorus from 20 ppm increase to a very high, um, 100 ppm or 200 ppm. I have to check on that. But at 60 ppm, the yield is the highest. Lower than that, yield was lower. Higher than 60, yield was lower. So that's our research, and then there are also research done in different labs in different countries on different cultivars. It's all demonstrated that industry been using— the level of phosphates the industry been using is too high. Too high, it's not benefit anybody because it doesn't give you higher yield, doesn't give you higher cannabinoids content. I know the fertilizer company is going to hurt, hit me here, but then I, I just wanted, you know, tell people from our results. And then also it's not only our results because this showed up in different other labs. They kind of repeated our research, not exactly, but got the same result. Yeah, I strongly suggest that people don't use more than 60 ppm. Because, you know, the legacy world, people use the high phosphate. It's not without reason. We all know that plant flower need phosphate. But yeah, sugar tastes good, but too much sugar gonna hurt you. Phosphate is the same. Yeah.

Yeah. And that doesn't even come— take into effect the, the fact that phosphorus, phosphate's a very limited resource that we have globally. We are overapplying it, and this is— a lot of it can leach into our groundwater, which leaches into our ocean and our water supply. It can create algal blooms, which create issues for marine life. So we need to be responsible with our phosphorus use. So plants need it, but you're saying 60 ppm is a really good level for optimizing yield without overapplication.

And that's true. Never go higher than that. Maybe some cultivars can do even lower than that. Yeah, I didn't mention the environmental part, but at least I want to emphasize that for cultivator, cultivators, if you want to make money, don't use more than 60.

You're wasting money spending it on—

Yeah, you are wasting money because you're paying more because phosphates are expensive.

Yeah.

And the same time you are not getting the yield even when you use less. So why would you?

I appreciate that. We have to look out for growers and the industry is very tough and anywhere where we can save money or increase yield is really important. So I appreciate that.

Yeah, because certain, certain conclusions I could say it's cultivar dependent. Try yourself. But for this one, I'm quite, quite confident that for vast majority of the cannabis we are growing, I don't think more than 60 ppm will bring you profit. Higher than 60, I'm confident on that because I read, we, I read so many people's paper on this issue. And they done independently at different stage of the plant even.

It's established science at this point because it's been replicated so many times.

That's right.

In your opinion. I love that. Okay.

But of course, if somebody design a research scientifically can demonstrate, yeah, higher can have higher yield, I'm always open-minded because You know, we, we, we have this handbook for cannabis production. We want these, the growers and students to get the scientific information from scientific source. So I'm always open if somebody done a research can demonstrate higher is beneficial and I'm open, even I say it confidently, we, I don't want you to use higher than that.

I love that. And you found with your research that you talked about today that some of the results you got were quite surprising. So we're always learning new things, which is why that's one of the things I love about science is it's constantly evolving. And I want to say thank you for your time. I will link to the papers, the textbook, and share your research. And I really appreciate the research that you and for our industry.

Thank you. You are good to talk to.

You as well. Have a wonderful day.

Take care, Ted. Yeah. Bye-bye.

That was Dr. Yubin Zhang with the University of Guelph, and you are listening to the Cannabis Cultivation and Science Podcast. If you like the podcast, please leave us a rating and review and give us a follow on Instagram and YouTube. We will have links to Dr. Zhang's published papers and open access research, and his cannabis production textbook right on the podcast page for this episode. And don't forget, at KISS Organics, we have a wide array of products we offer on our website, ranging from soils, amendments, and beneficial insects to soil test analysis and commercial consulting. We carefully research all our products we offer and manufacture to make sure that they are science-based and meet our highest standards of quality. Thanks for listening.