☁️VPD Misconceptions, Transpiration, and Ideal Environment, with Dr. Coco

12:12PM Jan 28, 2025

Speakers:

Jordan River

Dr. Coco

Keywords:

VPD misconceptions

transpiration

ideal environment

New Year's grow challenge

cloning challenge

temperature control

relative humidity

metabolic activity

mold mitigation

electrical conductivity

root zone

dry space

terpene volatilization

grow cast membership

Patreon

Greetings cultivators from around the world. Jordan River here. Back at you with more. Grow cast. I'm an island boy. Now today we have Dr Coco back on the line. Good friend of the show. He's here to revisit vapor pressure deficit. That's right, we went into it last episode, but this time, we're diving deep. This is 45 minutes straight on VPD, what it's actually good for, how it's misunderstood, and how it can be a bit of a red herring to some growers. It's a great episode. I hope you learn a lot. I know you will before we get into it with Dr Coco, though. Shout out to AC infinity, my favorite grow gear manufacturers, AC infinity.com, always use code grow cast one five. Grab yourself a new tent, a new light. Grab yourself a grow kit. Expand that grow room, get that veg tent going. So you can do some staggered runs. Code grow, cast one five works on all the products at AC infinity and the Grow kits, which come with everything you need to get started growing. Of course, AC infinity makes amazing, durable tents. They make the best oscillating and inline fans in the game, they make grow lights. They make grow pots. They got scissors, they got protective eyewear. Everything you need is at AC infinity.com, and code grow cast one five is the code you use to save everybody. You're helping us keep our lights on here, and you're supporting an awesome company, our partners, AC infinity. We've been with them for years and years now. I remember discovering them when they just had the cloud line. They're in line fans, and now they have all these goodies, from the cloud Ray oscillator to the cloud forge humidifier, find it all always use code growcast, one, five and thank you. AC infinity. AC infinity.com. All right, let's get into it with Dr Coco. Thank you for listening and enjoy the show. Hello, podcast listeners, you are now listening to grow cast. I'm your host, Jordan River, and I want to thank you for tuning in again today. Before we get started as always, I urge you to share this show. Turn someone on to grow cast. Turn someone on to growing it's the best thing you can do to help us on our mission of overgrowth. Make sure you're subscribed. Hit that follow button and big thank you to the members growcast podcast.com to see everything we're doing. All right, everyone, we got a return guest. My good friend, is back on the line, one of the most frequent guests on this show. I think if you total up all the appearances, you know Him, you love him. Dr, Coco is back. What's up? Dr, Coco, Hey,

Jordan River, I am excited to be back. It's been a minute since we've done a show. So yeah, I'm been on quite a bit, but I'm happy to be back, dude.

We love you. You're the you're one of the all time favorite guests. And weirdly enough, like art, we both got busy schedules, but it seems like we always find time around the New Year. You have the New Year's grow challenge every single year. And it's like year after year. I find myself around the holidays being like, Hey, you got time for a podcast? And then here we are the 2024, New Year's grow challenge about to kick off. First of all, how many have you done so far? Which? Which number is this?

This is the sixth New Year's grow challenge. Fifth or sixth? Sixth, sixth annual New Year's grow challenge. You're old, is what I'm saying. I know we're getting up there. Yeah, it's fun, man. It's, you know, New Year's Day. We usually wait for ball drop at midnight, and, you know, to drop our seeds right when the new year starts. Oh, that's fun. And everybody kind of starts at the same time. And we just grow together. We do different kind of things on the side during the grows, to have fun and to learn about growing. We call it the nearest grow challenge. It's really grow along. It's a way to bring new growers and you know, experienced growers together and share tips and tricks and get to, you know, support everybody through their grow.

Nice. Well, for the first time, listeners tell them where to go, obviously, Coco for cannabis.com. How to find the Grow challenge and then the side challenge you're doing? Yeah.

So you want to get in the New Year's grow challenge. You just go to Coco for cannabis.com. Forward slash challenge. You just click on the challenge button in the menu. Sign up. It's totally free. And this year we're sort of opening up different ways you can participate. So, you know, we'd like you to start a journal and tell us where you're going to be, sort of sharing your grow, whether it's there in the journal and Coco for cannabis, or a lot of people just want to, you know, post about their grow on Instagram. So they'll tell us what their Instagram handle is, or their YouTube channel or something like that. And then, you know, we all follow it around. We are all growing at the same time, and this year, we usually do different sort of side challenges. You know, we've done the party cup challenge a number of times. You've done the one cola challenge, where you grow like one plant in a specific way. This year we're doing a cloning challenge, so it's gonna be a little bit different. You know, the growth starts on January 1 and then on February 5. So just like 35 days later, we're going to have clone cutting day, where you try to take cuttings off of your plant and get them to root. So we're going to have some prizes for the smallest rooted cutting and the largest rooted cutting, and just have some. Fun. You know, get different people cloning in different ways and sort of showing it off. So, you know, if you've never done cloning before, this is gonna be a great opportunity to take some cuts, to see tons of other people, to kind of compare your process and to learn from a lot of other people doing it exactly the same time. If you have cut clones before, if you do this all the time, then, you know, try to take the smallest cutting that you can get to root, or the largest cutting that you can get to root, and, you know, teach all these newbies that are going to be trying to do it for the first time. You know, your your masterful methods. So that's really what the the Grow challenge is all about. We try to toss in some prizes there, but it's never for just sort of like being the best grower. It's, it's really about being involved and sharing what you're doing and being part of a community of growers.

Nice, man, I love it, and I love that clone talk. We're overdue for some so maybe we'll have you back on around that time. Oh, I've talked about, yeah, just talk about all the nitty gritty stuff. Talk about, you know, best practices? Yeah, we

could talk about different ways that people are cloning, yeah, how it worked out. Maybe right after the Clone challenge, we could, I could come back with sort of an after incident report and talk about what worked well, what didn't, or what different people had success with. But I'm really excited. I always get excited about seeing the side challenges. In the last spring auto flower challenge, we did grow the biggest auto flower.

How did that go? What was the top? What was the height on the biggest one? You know, we didn't do

it based on the height. Specifically, we did it based on, like, bulk of the plant. That's a pretty big plan. So, yeah, that was a fun demonstration to sort of show people that that think, you know, autos are always small, how damn big you can grow some these autos, if you really get your, your, you know, grow together as it were, hell yeah. And this cloning challenge, I think it's gonna be fun to see how fast people get roots in different styles. I think it's, I'm really interested to see who can get roots on the smallest cutting, who can get roots on the largest cutting. And since these plants are only going to be 35 days old that we're taking the cuttings from, like, how large can the largest cutting be? I'm looking for somebody who's going to, you know, chop their whole plant down and try to re root it, you know what? I mean, yeah, absolutely. Which I've seen. The biggest cutting is just, I gotta cut it at the soil, and now I'm gonna reroute the whole plant. Someone's gonna go for that. Yeah? Totally,

yeah. I like that, man. That's good stuff, and there's a million ways to do it,

yeah. So if you don't join the new year's challenge, come by, check it out. See how everybody's doing on these cloning adventures that we get into in the early February, and it's always fun get dozens of growers growing together.

Actually goes nicely with our subject, because I feel like what we're talking about today is probably particularly important during like that stage, the early stage, rooting stage, yeah, we're having you back on. Man, we're having you back on for a repeat topic. This usually doesn't happen, but I feel like it's well, well worth it. We're revisiting VPD today. VPD, those three letters. I

love it. VPD is, is such an interesting metric in growing. I feel like you know brand new growers don't know what VPD is. And then sometime, you know, maybe towards the end their first grow, or, like, in their second grow, or something, they learn about VPD. And then they think it's the end all and be all of everything, and it's like the only thing they need to know. So it's this. It's an interesting metric that growers seem to almost inappropriately fall in love with it's

really funny that you say that. And I want to say, like, we're gonna for all my VPD heads out there. You know, I'm not, I'm not trying to ruffle any feathers here. We're gonna go over like, where it is genuinely useful. But that being said, Coco, I gotta agree with you. I find that a lot of growers discover VPD and see that chart and then do something to their grow. It's kind of like a red herring. They might change their grow in a way that is actually not beneficial for the plants. So that's what inspired me to revisit this

chasing VPD. You can definitely get either your temperature or your relative humidity out of pocket, out of sort of the acceptable range, and that can cause problems for itself. So that's a really important point. I think everybody, I think it's brilliant to start there. Climate is important for lots of reasons, and VPD is is one metric that we measure climate with. It's really important for transpiration. VPD basically determines the rate of transpiration from the plant, and so it's an important metric, but temperature and relative humidity, which. Which sort of are, what makes up VPD. VPD is, you know, the the result of the intersection of the temperature and the relative humidity. But relative humidity and temperature are both important for a lot of other reasons, independently, right? Yeah, independently of transpiration. Yeah. So VPD is important. I think it's important for growers to sort of have a working understanding of how VPD operates in their grow. There's, you know, some ways that we can manage VPD, or we can manage other things when we can't manage VPD, so being aware of that, but you can definitely get yourself into trouble if you're just chasing a VPD target, and if you put VPD, as you know, the highest goal, and stop paying independent attention to relative humidity and temperature,

and that's what I want to go back over today. You had some really good stuff to say last time. But let's start with a recap. Like, let's define VPD, vapor pressure deficit, like you said, an environmental metric. That's the first takeaway that I want to put out there. Some people talk about it almost like they're talking about like, leaf tissue, nutrient content. Like, this is the target, and you hit the target. It's like it has nothing to do with the plant, necessarily, it's an environmental metric. And then they've found that transpiration does well within this range. Generally. Is that an accurate way to put

it? Yeah, absolutely. VPD is describing the environmental condition of the air. And basically, I think that the helpful way to kind of think of it is VPD is is how thirsty the air is. Oh, I love that. That might be a little bit weird, but high VPD is really thirsty air. Low VPD is, is not thirsty air, right? It's already wet air. So if you think about it like that, yeah, I think it can help you sort of manage your grow in in some way. So high VPD thirsty air is caused by high temperatures and or low relative humidity, right? So if the relative humidity is low, the VPD is going to be pretty high at any temperature. But if the relative humidity is low and the temperature is high, that's that's really thirsty. Think like, you know, Arizona in the summer, right? Hot, dry air and water is just going to evaporate into it very quickly, right? Right, low VPD is wet or cold air, so a high relative humidity or a low temperature is a low VPD. So think, you know, like some place cold and raining, like, yeah, in the winter, maybe yeah, if you don't, if you take a shower and you draw yourself with the towel, and you hang the towel up on the rack, the towel is gonna get mildew the next Yeah, right. It's not even gonna dry, right? In Arizona, the towel is dry again. You could take another shower right away, and by the time you get out of the next shower, towels dry again to dry you off, right, right? The sucking of that water out of the air, right? That's the vapor pressure that it's referring to pressure deficit. Yeah, yeah. Literally, when the when the pressure deficit is very high, it's literally exerting pressure to suck that water out of whatever. It sucks it out of your clothes. It sucks it out of your plant. It sucks it out of your swimming pool, your lawn or wherever, right? It's very dry air that's forcing that, that evaporation, all right? And that's important. But now VPD is entirely determined by relative humidity and temperature.

And it's a wide range on that green part, right? It's not just oh yeah, good. VPD up towards the high temperatures, you can still be in the green and be pushing yourself into a low, low temperature that cannabis, for instance, probably won't like

Absolutely. So we talked about sort of high VPD is, you know, high temperatures or low relative humidity. A low VPD is, you know, low temperatures or a high relative humidity. But what you know, say, an ideal VPD, an ideal VPD could be ideal temperature and ideal relative humidity, or it could be way too hot and way too wet, exactly, or it could be way too cold and way too dry, but as long as you sort of match those up correctly, you could still be at the ideal VPD, right? So you don't want to be, you don't want to be too hot and too wet, that would still give you the same VPD potentially. Say you want a VPD of one, well, you could get to a VPD of one with, you know. Really hot grow that has a really high relative humidity, or you could get to a VPD of one with a really cold grow with a really low relative humidity, exactly. They aren't all going to grow the same way at all. So, yeah, it it can't become the driver of the bus. It's got to be a passenger on the climate bus here, as you're managing your grow. It's one of the things that you want to be aware of. But, and I remembered last time we were talking about this, we both agreed that temperature really should be the driver of your climate bus.

Yes, that's what you said last time. Temperature is king. And that is so true. Because what I want to push back and have the takeaway for you know growers who use this chart from this episode to be is they, if you look at it like, as long as I'm in this green I'm good, you're working backwards. And my biggest pushback to that is, look at this chart. Look at all the different temperatures. Doesn't it depend on your cultivar? I mean, if you're growing something from Afghanistan like I you tried to grow in my cold Illinois basement, you're going to run into issues with the plant not being happy because of its lineage. It's accustomed to something warm. I don't care how good the VPD is, if you put it in a cold space, it's going to be pissed off. So I experienced that personally, I feel like so I guess that's my next question. Is, like it's cultivar dependent? No, I've certainly experienced plants that like it a little bit warmer or a little bit cooler. Sure,

I think that that's even more true if we were really cultivating different crops, true, but we are generally cultivating cannabis, and like you say, there's going to be temperature differences in terms of where they'll be ideal for different varieties, slight ones, yeah, yeah. But they're not as significant as if you were growing, you know, like avocado, lettuce and calorie together in the same space, or something like that, then you'd have sort of bigger climate differences between what really crops needed.

But you say temperature is king, and like, cannabis likes it warm. They like it warmer than we like it when we're wearing clothes, you know what? I mean, they like a warm environment. And a lot of people are like, I wanted to get that VPD right, so I cranked my temperature down. It's like, You're slowing growth. You're slowing the driving of the of the photosynthetic process. And I don't know that's just what I see. And I want to keep growers from falling into that trap.

I absolutely agree with that. You know, I really kind of think that in terms of the numbers, I don't I don't think you have to become too particular about knowing what, what number VPD you're sort of aiming at, or where you are. I think that to a certain extent, you should understand the principles of VPD, but let's get into that a little bit. So if you have a temperature range and you're able to maintain your grow within that temperature range, say, up to the low 80s, it lights on, and maybe, you know, not much below high 60s at lights off. Sure, that's a pretty decent temperature range, good

range under LEDs, especially that's that's a good tent, like general home setup,

yeah. And if you're right with the ventilated grow, yeah. And if your relative humidity, ideally, we start it high, and it's sort of inconvenient, because the plants do the opposite. The plants put out most of the humidity. Laid in the crow when they're young, they don't put out a lot of humidity, but they want more humidity. When they're older, they put out a lot of humidity, but they don't really want as much. True. So early on, a lot of growers have to add humidity when they just have seedlings, right? We're trying to keep humidity like real seedlings, maybe 75 and then as the plants start to get into veg, you know, we're like 65% humidity into flower. We're usually going to drop it, you know, below 60, or at least down to 60. And the reason there is mold mitigation, we're trying to hedge against getting bud rot, and that's really why we're dropping the relative humidity and flower. It's not because it's better for VPD or something, or it's better for transpiration. The reason we drop humidity is because we risk bud rod if we don't drop humidity, good point dropping humidity. And if you're really following sort of VPD recommendations, which, again, Jordan and I both just said, don't really do that, but VPD recommendations often then suggest going higher with VPD late in flower. And that's not about VPD at all. That going higher with VPD late in flower is because growers lower their relative humidity to prevent mold. Lower relative humidity at the same temperature produces a higher VPD, right even the chart that's telling you like via 1.2 in early flower and. 1.4 1.5 in late flower. The reason they went from 1.2 to 1.5 has nothing to do with transpiration, and frankly, it has nothing to do with VPD. It has everything to do with you need to lower your relative humidity to prevent Buddha. Wow. I needed to say that. I know, but that's that's why it's you're not really using VPD anyway. So even the VPD chart, even the guide there, it's making those adjustments, because they know that, you know, at those last few weeks of flower, you're gonna be running at 80 and like 50% humidity, which is going to be one point whatever, VPD. So they want to sort of tell you to go there. But the problem is, they don't tell you how to get there. Yes, you could get to, you know, 1.5 VPD by cranking up the temperature at the same relative humidity, or cranking down the relative humidity at the same temperature. And that that's, again, my my VPD is kind of a way to describe your grow. But it really shouldn't be the thing that you chase. It can

be a red herring 100% now, should they add, should they add this asterisk? Tell me if this would solve the problem in your eyes. In order to use this chart properly, achieve your ideal temperature, and then adjust VPD using your changing your relative humidity, this

is what I actually think Jordan set your temperature, set your relative humidity, and then, if you're curious, check and see what your BPD is.

That's exactly right. If

you follow the rough guidelines that I just laid down for temperatures and humidities at different stages of the grow, you're gonna be in the green zone, or close to the Green Zone chart, yeah. Anyways, absolutely, because you're setting the temperature and the relative humidity, right? The issue with sort of VPD is growers, most growers, have an easier time controlling temperature than they do controlling humidity, to the extent that they can control anything in their in their gross faces. Anyways, that's a good point. So when they're chasing VPD, it's like they don't have much of a lever to screw with the humidity. Often the lever that they can manipulate is the temperature, and so that's what they end up doing, which is the opposite of kind of the advice that you laid down, which is good advice. That's a

really good point. They'll just turn down their light and turn up their their their exhaust fan. That's why it's good to have a humidifier or a dehumidifier. I think you

need a humidifier for early on during the grow. You know, if you're investing in technology, I'd really suggest getting a AC as your climate control motor. You can use your air conditioner as a dehumidifier. Basically, I mean air conditioning dehumidifies because the the colder plate reaches the dew point and condenses water. So, yeah, you know, air conditioners always condense water, and that is dehumidification. They actually do it as efficiently as dehumidifiers do. It can make the space too cold sometimes, but, and you can add some heat if you need to, but, yeah, you know, I do think it's easier to manage climate with an air conditioner, but then that does put you more in control of temperature than humidity. Yeah?

And really, it's like, a lot of this is, is geographic, like you said, Arizona and New Mexico coming online when we get, like, an influx of new members from these desert states, yeah? I almost have to, like, reframe my whole thinking, yeah. I'm like, Okay, we're in, we're in the desert. Now, you know what I mean. I'm used to in Chicago, it was the reverse. The driest time of year was winter, when it was cold and dry, right? They have hot and dry. It's beautiful, you

know, if you're in the Midwest, the winters there are perfect for growing nice, dry, cool air. That's kind of like ideal. It's great for being able to set the right temperatures for your dry, you know, at the end of the harvest, yeah, overheat your buds and all that. So there's definitely advantages there. But yeah, I agree. It's the other side of the spectrum. Growers in Arizona, for example, are almost all doing that. I work with at least like the home growers are doing ventilated tents in air conditioned houses, and they're exhausting this hot, you know, wet air back into like one room in their air conditioned house, and that sometimes is an issue, so we have to get it back towards the return to that system, or put a little duck boost fan into the duck that's going into that room, or Different things like that. So there's definitely different issues different parts of the country, different climates, have to manage, but most of us, I think, are still it's a little bit easier to manage temperature often than it is to manipulate relative humidity, at least to manipulate relative humidity down most of the time. Yeah, that's exactly

right, and I think that's. Why it's exactly why people go down that road to changing the temperature and then sometimes shoot themselves in the foot. So I just want to, like, get people focusing, like you said on the first episode, temperature is king. Like, get that locks down first, adjust the humidity from there, and then be aware of your of your local environment and your seasons, because that's going to largely dictate what you need to do to gain optimal environment settings.

There's at least three things that you want to keep in mind when you're thinking about climate and like at least three, but these are three big ones. One is transpiration, and transpiration is really regulated by VPD, which is the combination of temperature and relative humidity. The other is metabolic activity. And metabolic activity is going to be in the sweet spot when the temperature is right. So you really do want to be in the, you know, near or in the low 80s under LED light during the the photo period to have the best metabolic activity. Relative Humidity is hugely important for mold and mildew. You want to be able to prevent and mitigate against the risks of mold and mildew. So we have kind of three important climate related crop management issues, we have ideal transpiration, ideal metabolic activity and preventing mold and mildew. They're all related to either temp or humidity or both, right? So we need to be able to kind of keep

plates spinning. They all have to spin. You can't completely neglect one, or else you're gonna end up with broken plate on your floor Exactly. That's a really good analogy. And

there is, you know, good temperatures to be at if you can, if you can reach those temperatures and then try to manipulate your relative humidity. Usually, our efforts to manipulate the relative humidity are to try to lower it, because the plants are produced a lot of humidity, and we need to take that out of the system, right?

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one of the reasons that I like to teach beginner growers, especially how to clone and take their cuttings and go for another run is exactly what you just said, like you're learning to spin all those plates. I think it's a great place to start to learn the intricacies and tendencies of one cultivar, and really get to know what this plant likes and how to make it happy. I think the more variety of cannabis you grow in your tent, and like you said, especially if you start growing other plants, you're going to be challenged more. You're going to run into more issues. You're also going to learn more if you you know, solve those issues and work through them. But I think for a beginner, it's good to stick with one cultivar for a minute and run it until you can get it through the whole cycle without any scorch or yellowing or it's just praying the whole time. You know what I

mean? Yeah. I mean, absolutely figure out how to keep your plans happy. That's really what it's all about. And I. I do think it makes it easier to to sort of simplify things, to be working with one cultivar. Almost every grower wants to have six different strains to smoke those. They want to grow six plants, right? You'll

see the diamond when you run those six different packs like and the the environment's probably one of the ones that's like the least, the least changing. I certainly see differences in feeding. Like, one plant will feed much heavier than another, or want, like, a really specific it'll run out of, like, zinc, some micronutrient, right? Like, clearly it was heavy feeding on the zinc, less

of that in high frequency fertigation, I will say, because, yeah, you're just sort of providing better access to everything. And is not sort of a set stock amount of anything in the media to kind of deplete, if that makes sense. So

put them in cocoa with high frequency. Fertigation is what you're saying with seven different strains. That's the move.

I think if you want to grow seven different strains, it definitely helps to be growing with fertigation, as opposed to amending for the reason that you're saying different cultivars will sort of deplete amended soils at different rates totally. So it becomes harder to manage a mixed cropped room. But when you're fertigating, you're not going to deplete the nutrients. You're replenishing them with every feeding of and, you know, I've done several commercial facilities where the SOP is to grow eight to 10 strains together in a flower room, all on the same diet,

right? Yeah, that is a really good point. I hear a lot of breeders saying, you know, I Pheno hunt, especially like in smaller pots with fertigation for for many reasons, one of which being what you just said, like a consistent diet. And then, like you said, when you switch outside of cannabis, that's when, I mean, I think there are some plants that just aren't feasible to be grown together, to be honest, right?

Absolutely. Some plants really have different climate requirements, you know, especially perennial plants. Annuals often are sort of can grow in the warm growing climate in lots of different places, and they just die before the seasons change. But yeah, there's definitely differences between what kind of crops can grow in different climates, for sure, and if you were going to try to grow those things indoors, you'd have to tailor your climate to them, right? Cannabis is fairly easy, you know, because it's a little bit warmer and a little bit more humid than we like, and they create their own humidity, and the lights create their own heat. So it's kind of in the sweet spot. It's it would be easier than growing a lot of other crops.

That's how I certainly how I feel. I don't think we've done like veggie cast with you, at least for a while, and we hear about tomatoes and peppers. I think a lot of cannabis growers jump over to those. Yeah. But what do you like to recommend cannabis growers grow, maybe even in like a cocoa setup like you're doing, that they could easily transition over to.

Certainly, tomatoes and peppers are pretty high value, and they they offer a huge quality, you know, improvement over what you can get at a store. Tomatoes. In particular, there's nothing like growing your own tomatoes, even if you don't. I don't really like tomatoes, but it does because you generally get gas green tomatoes, homegrown tomatoes are just like, a different, different fruit. I mean, they're just like, not the same thing. So, yeah, those beautiful, you know, a lot of the the squashes, and I'm kind of thinking specifically here about the crops that do well also with our runoff water, because we get a lot of growers that want to repurpose their runoff, yeah. So squashes, tomatoes, peppers, some, some of the, you know, other kind of veggies, like you can grow some flowering veggies, like broccoli, cauliflower, stuff like that. Not legumes, though, certainly not with our water that we'd want to use, but fun things to grow for other reasons, and maybe leg used to be something more of the alley of the the organic growers, the organic indoor growers that want to look at sort of mixed crop nitrogen fixing strategies, yeah,

right, because they specifically pull atmospheric nitrogen and Put it in their little root nodules for decomposition

later. Basically, they form symbiotic relationships with bacteria that fix nitrogen and store it in their root nodules. Yeah, exactly. But that happens because the beans are are there, the legumes are there.

I like a good legume, man, let me tell you, and you're right, tomatoes, peppers, these are all things I eat. So this is good. This is good stuff. Here's your unexpected legume. Yeah, peanuts, for sure, the delicious and robust peanut, my man, George Washington Carver knows what's up the greatest legume, some might say, yes. Man, we've got, we've got all over from VPD. What are we talking about? We

were talking about VPD. I have another I remember the last time we were talking about VPD, I made this point to VPD controls transfer. It controls the transpiration out of the planet. And so it's basically a measure of how fast the plant is going to lose water, assuming it keeps its stomata open. If the VPD gets really high, the plant will shut down its stomata to prevent dehydrating, essentially, especially if it doesn't have access to a lot of water in its roots. So this is where I'm going with this. VPD determines how fast water leaves the plant. Electrical conductivity of the water determines how fast the water can enter the plant through the roots. Wow. So then one of the reasons is really the reason that we measure electrical conductivity, it's not to know how much nutrients are in the water. A lot of fertigators believe that they're trying to measure like the dose that they're giving. It's not about that. You're measuring basically how hard it is for the plant to absorb the water. So that EC is like the other side of the VPD coin. If VPD is on one side of the coin, EC is on the other side of the coin. VPD, a high VPD means a lot of water is leaving the plant, and you need to pair that with a low EC, because a low EC will allow a lot of water to enter the plant a high EC, it's going to be harder for the plant to get water. So when the plants losing a lot of water to transpiration, you want to lower your EC in the root zone, and if there's nothing else you can do so you're dealing with, you know, high temperatures, low humidity. And you know, you've got all your climate control devices cranked up, and you still can't manage it, then that's what you've got to do. You got to lower your root zone Ec so the plants can have an easier time taking up water, so that, you know, they can still push that that much water through themselves. Essentially, that is fascinating. If you're in the opposite situation and you're fertigating. So if you get in a situation where you're you're dealing with low VPD, and you can't, you can't change it, you can't raise the temperatures, or you can't sort of lower the relative humidity, then you should increase the EC because the plant is going to be taking up less water. It's going to be sort of transporting less nutrients through its through its xylem, because it's taking in less water, and increasing the concentration of the nutrients will allow it to sort of take in more nutrients, no

nutrients. I totally see what you're saying, and that that's like when your plant is looking all droopy and sad and it's not driving from the cold wetness. I've seen what that looks like, what you're describing, and you want to raise the strength of the solution, if that's the case, to be able to still deliver those nutrients,

and not to be sort of putting too much water into the plant, because the plant's not going to be able to get rid of that water because the VPD is too hot. So that's one of the ways that you know, beginning the conversation was saying, like, it's one of these things that's good to know, sort of, theoretically, I don't think you need to know your specific number, but this is one of those cases. If you know, my tent is running hot and dry these days, right? Because it's hot and dry out suddenly, or whatever, then lower your EC. And that's something that happens to a lot of growers, and that can really kind of help get through those more difficult moments like that. So there's a relationship there. And if you think about VPD as Yeah, one of those key climate variables that determines how fast water moves through the plant, and EC is really the other one that determines how fast water can move through the plant. So, yeah, that is that's great. It's helpful to sort of understand how they they interact with each other, like that. You know, during the dry for example, when we're drying our buds, we often talk about like 60 and 60 in terms of temperature and relative humidity, the way moisture is leaving the buds is really a function of VPD, right? Still, right? It's vapor pressure deficit. So that's another time that you know you could be aware of if, if, like your your room is too hot, then you hotter than you would want it to be during the dry, then you may want to keep the humidity a little bit higher. If it's too cold, then you may want to keep the humidity, you know, a little bit lower.

That's that makes perfect sense. Uh, VPD, during the dry, that's another game changer. And I like the first thing you said about get your temperature on point, then dial in your humidity. If you're curious, take a look at the chart. That's like the big the big takeaway, yeah, but I love that too. Applying it to your dry space. I almost never hear people talking about their VPD in relation to their dry space, and that's probably where it's more of a direct example than anything, because the plant isn't doing anything else. It's just water. Just water leaving the dry. Yeah, yeah. Now dead bugs. You

really don't want to if you have too low of VPD, you're going to get mold potentially up too high of VPD, it's going to be, you know, too fast of it dry, and it's going to be a harsher smoke and all of that. So and you know, growers, almost all home growers can't reach the ideal sort of 6060, that's often bandied about for drawing like there's just no way they're getting to 60 degrees unless they're living in Chicago in the winter, like they're not going to get their air conditioners down to 60 degrees and keeping that so if you can, you know, just Understand how to make those adjustments. You don't have to make big adjustments either, but there's a relationship there. Yeah, fine tuning it, yeah, both temperature and relative humidity combine to determine how fast water evaporates. Essentially,

that is a great point. And I tell people all the time, if you don't have to, like, drive yourself crazy for that 6060, dry, if you're really, if you're under 70, if you're, like, 68 and below, I'm happy for you. If you're at 50 to 55 really relative humidity, you're fine. That's usually what I tell people. I

agree. I think it's just you're gonna be done a little bit early if you're there and, yeah, just stay on top of it in in all these conditions. The other one you know, is when growers are too wet in their environment, or whatever they they often, you know, if they're in that humid area, they might not be able to get down to 60% humidity. Oftentimes, you can, if you're running air conditioning, but, yeah, those are all all things you can be a little bit outside of that range. But again, temperature is important when you're drawing there too. It's not just VPD. You don't want to be at 120 degrees Fahrenheit, because that's the only temperature you can get the VPD right, or whatever, because you're going to burn off a bunch of other things. So you still want to be at or about there, but to the extent that you can't get one of those match breaks exactly on par, you can adjust the other one a little bit to still have the same VPD. That's if what you're worried about is the evaporation. And yeah, I think we're a little bit more worried about the evaporation during the dry than we are about the transpiration during the grow. At least there's, there's other things, like the metabolic activity that we need to be more aware of during the grow,

right? It's more of a one to one comparison. But I also think about that vapor pressure deficit, which, by the way, isn't a pressure deficit, just a vacuum Yes. So why isn't it, you know, the vapor vacuum. So I think about that vacuum that's occurring and how that affects the Trichome heads, right? Because you're right. It's like we worry about light and we worry about heat volatilizing the terpenes in there. But do you think that the VPD is, you know, sucking terpenes out, if it's two, or am I way off base here? No.

I mean, I definitely think that. Well, it's good. Temperatures going to have an effect on the terpenes and the trichomes too, probably

primarily, I

imagine, yeah, they, they're, they're potentially areas where getting it very dried out from low relative humidity may happen. But that, that is another thing. I don't think it would be just VPD, but, like, it's involved with VP

Right, right? The volatilization is probably easier if there's a vacuum along with it. That's a really astute point. Yeah, I was just thinking about that vacuum, right? And then they're like, waxy membrane of the Trichome head and how those two might interplay, yeah?

Well, you're not actually getting, like, a Kirby in there, like, you know, sucking them off correctly. Yeah, no, I hear you. You know, that's what I've often said. We want to really keep things comfortable for the plants. We don't want to be putting, you know, undue pressure on them from any of these directions. And I know a lot of growers think that selective or appropriate stressing is going to be kind of the the key to unlocking the magic. I really think the key to unlocking the magic is to to keep things kind of more down the middle of the road to keep the plants happy, to not kind of do put undue stress on them. And, you know, I don't know what sort of a radical VPD would do to like the trichomes or the the terpenes themselves, but you know, the heat alone is going to burn off a bunch of stuff. So, right? Right, that is, and I think that that was one of the main points that you wanted to nail. If you just pay attention to VPD, you can really get these other things out of out of hand. And the other things are important in their own right. So pay attention to temperature, be in the right temperature, and then you can think about some of these other things. Man,

I love it. That was, that was everything I hoped for in this episode, and more 45 straight minutes on vapor pressure deficit,

a little bit into sort of some other gardening stuff and growing. Oh, yeah. Oh,

hell yeah. No. I think you gotta, yeah. I think we gotta get back on Dr corn cob and talk about some corn breeding or something. Next time, no, next time. Let's do cloning. And yeah, and I would, I would like to revisit those episodes. Someone just wrote me about them, where we were talking, speaking of corn and stuff. We were talking about the different agricultural history, basically different agricultural revolutions. And people really liked that content, too. So maybe after cloning, we can revisit some of that stuff. I'd

be really thrilled to Yeah, I'm always excited about talking about sort of where plants have come from, and what we can learn as as home growers from all of that. I think it's fascinating. So I'd love to come back on talk about any of those things. I definitely like to come back on talk about cloning. It's been a while since I've done cloning my own grow. So I'm really looking forward to it. Oh

yeah, we've got to see that cocoa clone set up. Man, there you go. It's good. It's good stuff. Well, one more time, cocoa for cannabis.com. New Year's grow challenge. Give us the rundown. Yep, starting

January 1, if you're a few days late, you can always jump in and be part of it. Free to join, grow any seeds you want to. We do have a couple of official strains from homegrown cannabis company, but grow any strains that you want to. A lot of people grow all sorts of different things, and it's just a fun time to start growing together. We're doing the cloning challenge starting on on February 5, like 35 days after the main grow starts, and there'll be prizes and just fun to be had. So sign up at Coco for cannabis.com, forward slash challenge. You can also check me out on YouTube at Dr MJ Coco, on YouTube and on Instagram at Dr MJ Coco, and here on the Grow cast podcast with Jordan River. I always

welcome. Thank you, man. This is a dope episode. I appreciate you. Anything you need, just hit us up and yeah, we'll see you in the challenge one

more drop, I have invite people to come and check me out on Patreon. I do the Ask Doctor Coco show every week on Patreon for my subscribers, and it's the best place to kind of track me down, be able to ask questions and come and show your grow and really get kind of that, that one on one consultation. So if you're looking for that, check me out on Patreon. All

right, everybody, go check it out. Coco for cannabis.com. Get in on the challenge. Check out the Patreon. Thank you, Dr Coco, we appreciate you, man. We'll have you back on real soon. Okay,

absolutely. Jordan, my pleasure and grower. Love to you and everybody out there. Happy New Year.

See you guys. We'll see you next time. Got some more growcast Coming at you, so don't touch that dial. This is Dr Coco and Jordan River signing off saying, Be safe out there, everybody and grow smarter. That's our show. Thank you so much for tuning in, everybody. And thank you to Dr Coco, of course, grow cast podcast.com for all the things jump into membership. We got a link right up there, hundreds of hours of bonus content. We got member only videos, giveaways, Hangouts, everything you want, plus more, it's waiting for you in membership. Plus you get $20 off per pack of grow, cast seed, co seeds. We just dropped the apes in space line. Go and grab some apes in space. And if you're a member, you get $20 off per pack. So grow cast podcast.com, for everything seeds, the membership and everything we are doing that's all for today. Be good. Be safe, happy. New Year, everybody. We'll see you on the next grow cast. Bye, bye. Now you

that's a pretty big plan. I.