Vapor Pressure Deficit (VPD) and Cannabis Cultivation

[@stanbyme3414]

Great information on vpd,I love your speaking voice, easy to listen and compute!

[@luckycbr600rr]

Ah.. thank you very much for sharing this knowledge to every one.. i have been playing with vpd in my grow tent for a year now.. i have better understanding now..

[@dh18436]

Here's an easy way to understand what VPD is as a concept if you had trouble with this video. Relative humidity is a percentage because it's the ratio of how much moisture the air contains compared to how much it CAN hold at the current temperature. VPD is basically the other side of that coin - it's a measure of how much MORE moisture the air can hold at a given temperature.

[@nate6748]

Thanks! Super helpful

[@dampbutthole3025]

so she said a vpd of 1 is usually a good set point. but do you try to maintain 1 the entire grow? or change it for different stages?

[@LifeOnceLived]

@@dampbutthole3025seedlings .80, veg .95/1 flower 1 to 1.2

[@nate6748]

1 is generally safe all-around, but there's a range! You can go lower for clones/seedlings, like 0.6 - 1.0 kPa. Vegging plants stay happy around 0.8-1.2 kPa, and flowering plants can go higher - 1.2 - 1.5kPa. I like to envision a spectrum from hotter + wetter, to cooler + dryer, as the plants go from seedling to vegging to flowering @@dampbutthole3025

[@TooBanger]

@@dampbutthole3025Different VPD for different stages. You want a low VPD 0.4-0.8 during propagation/early veg so the plant focuses on root development. 0.8-1.2VPD for Early-Late veg and 1.0-.1.5 for early to late flower. She states in the video that having a higher VPD to prevent molds can actually have a ironic effect. So, a VPD of around 1* is good. Each plant is different.

[@kaybailey2660]

This is completely gold 🙏💗🌱

[@magnumopus9631]

when i did vdp my garden went to next level

[@ryanmoore7098]

This was extremely helpful! She’s a godsend.

[@Ghade3245]

Great information very knowledgeable 🌟

[@Werdnasemajjamesandrew]

Thank you for your work doctor greenthumb

[@nihilityjoey]

I would really like to know how defoliating affects VPD. Especially as its a common practice said to increase yields. Leaves are important for so many things so im just wondering why this practice is said to do this.

[@samburgner8179]

Doesnt affect VPD. Plant will evaporate less overall because of less leaf area, so if the humidity drops as a result of that then the VPD would rise, but you could dehumidify less and the VPD would not change. VPD is an indicator, not a measurement. It relies on stomatal conductance, leaf temp, air temp, vapor pressure in the air. Many ways to change VPD, but defoliating is not one unless you change your environmental management too.

[@johnkunn2499]

People like Nadia: 10/10. Next level West Coast growers: 10/10. This video as useful educational material: 4/10.

[@lanzjeff0]

Thank you for the knowledge drop I live in canada and in the winter I have a hard time keeping rh over 25 % and definitely noticed a nutrient deficiency I think it's time to get a good humidifier and if I understand right around 50 % rh at 70 degrees Fahrenheit should shock the plants less ??

[@bennyb6071]

Eastern Ontario by late june with the right humidity pressure my plants grow 2' in a week, its crazy

[@MatanuskaHIGH]

I actually feed less when humidity is that low. Plants seem happier than normal feeding as they can’t uptake with low RH.

[@MatanuskaHIGH]

I’m in Alaska and the colder below freezing the drier it gets. So my vpd fluctuates constantly. Humidifier and demumidifier plus AC and heater are needed to keep a constant VPD. Gets expensive lol

[@allxdup1909]

@@bennyb6071 early flower I often see 3-4"/day with my indoor setup

[@natel9019]

There are charts online that tell the RH you want for the temperature your room is. It will optimise the amount of gas your plant can uptake. Which in turn will make you have more nutrient deficiency's because your plant will be able to increase the amount of photosynthetic reactions that take place thereby using more nutrients.Just a heads up.

[@tomactually9285]

There are lot of free charts showing optimal RH for varied temperatures available on the web

[@RONNIEJNZN]

Since were discussing VPD measures in kilopascals, would an exhaust fan creating a negative pressure in a grow tent effect the VPD measurements ? I have a 4 inch ACInfinity inline fan and on speed 3-4 , if I pull out the tent sides, they suck right in.

[@TooBanger]

Interesting. I would like to know this also.

[@CFDISAAC]

Speaking of double whammy.. Trying to get RH down later flower, when buds are larger and denser, you need HVAC super power to get to a 1.0 vpd due to the fact you need your temps sub 68 degrees, the point at which you can get PM or bud rot if your humidity gets too high due to failure somewhere in HVAC system. Therefor, you need massive HVAC ability to remove quickly enough, the RH in the room from feeding, if you want to run for instance, a 62/63 temp at 45% RH late flower. Having RH above 65 late flower has been no good, giving us yeast and mold issues and bud rot with some. A 1.2 kPa is far easier to get while also doing away with money sucking failed tests. For instance a 75@60. The units can dehum easier, and you have a good RH to deal with. You however lose some of that shock we like to put in the plants to up our test results as well. Lots of variables..

[@allxdup1909]

Not a word about leaf surface temps, which is a major factor of VPD. Think of a triangle, where you have to keep 3 factors constant within a parameter- air temp at top of canopy Relative humidity at top of canopy leaf surface temp at top of canopy you are looking to maintain 1-2 degC cooler leaf surface(LST) than ambient. Everything can look fine in the numbers if you ignore LST, but maybe little growth.. then you check LST and find it is 5-6 degC below ambient, then you realise why LST is also on the VPD chart along with air temp & RH.

[@drgreenhouseinc]

True, I didn't talk about leaf temperature. You are correct: Technically speaking, it is the saturated vapor pressure at the leaf's temperature that we should be using to calculate VPD. But plus or minus 2 degrees doesn't have a major impact on the overall VPD (eg. 1.0 vs. 1.05 kPa isn't going to make a big difference in plant transpiration or health). Also, many people do not measure leaf surface temperature, but they do measure air temperature and humidity, so it's much easier for people to figure out VPD from these parameters. Ultimately, I'll be happy when the day comes that EVERYONE is using VPD as a plant growth metric, whether they use air or leaf temperature.

[@allxdup1909]

@@drgreenhouseinc How can you call it VPD without knowing or addressing LST. maybe .05kPa is insignificant, but you only have to look at a VPD chart to know how much difference 1degC LST makes to the VPD, because they are 2 different charts... I think I'll refer to the Dr that made the charts on this one, his opinion here is obvious. When you have seriously tried to use VPD to guide your grow, including LST, you find out just HOW hard it is to get & keep right. Keeping an ambient temp & RH stable is easy- but that aint VPD.

[@samburgner8179]

@@allxdup1909 Yeah the leaf temp is critical and even more so between the top and bottom of the canopy. VPD doesnt drive transpiration when the lights are off either, only heat flux.

[@jonathanschadenfreude9603]

spring in vermont can be interesting .........great video

[@koojc7456]

Common sense would say osmotic pressure will have to be taken into consideration as well? How do the 2 relate??

[@samburgner8179]

Common sense says VPD is not that useful since it still is only a reflection of temperature and humidity measurements

[@jonathansanon157]

where do I put my humidifier and dehumidifier can I put them close to them?

[@laurieedeburn2449]

thanks

[@markwhitney5821]

Info was great thank you will use!

[@MrBLawson85]

6:45 - experiencing this right now!!

[@TooBanger]

How’d you go

[@MrBLawson85]

looking back at it now, my problem was dry environment not enough water@@TooBanger

[@chris432t6]

Good info although i was hoping for more numbers?

[@mopeaceproductions218]

Thanks for this now as a person like me a beginner grower I w I uldhave to get a instrument to use the VPD CHART? Is there another way I can do this if I Need,? If I can't equipment? And again thanks for this lesson #YouDig

[@MrPablo1uk]

A thermometer and hydrometer, often packaged together as 1 item

[@keepvibin100]

Great info 🌵🌵🌵

[@1ntwndrboy198]

Trying it in a room with a dryer blowing a lot of moist hot air I call it low stress training

[@SlapRoundTheChops]

So just add humidity?

[@veela420]

Gold

[@surronzak8154]

Hello, could negative pressure ventilation (in a grow room or tent) influence VPD ? Could there be relations between the two we could control ?

[@samburgner8179]

Not really. VPD calcs account for atmospheric pressure so if you drop the pressure it will reduce the vapor pressure in the leaf and outside it.

[@surronzak8154]

@@samburgner8179 yes but the LST and room temp remains the same

[@samburgner8179]

@@surronzak8154 They would both cool down under lower pressure?

[@surronzak8154]

@@samburgner8179 I need to check this but I currently don’t have a powerful enough exhaust fan, you maybe right, could the leaf transpire faster thanks to lower pressure ? Resulting in faster cooling

[@samburgner8179]

@@surronzak8154 Well its all feedback controlled so the faster it cools the faster the transpiration rate will slow. You were right that the light intensity affects the LST more.

[@JohnDoe-mc7tp]

NICE

[@MatanuskaHIGH]

Vpd is scary for cannabis for sure. Finding the happy middle. I like my humidity 55% but temps in mid to high 70s. If I get over 65% I worry and when lights shut off the the humidity should stay below the temp as if it goes above the temp that can cause issues. Juggling the VPD take the proper equipment and can be expensive on a large scale. Humidifiers dehumidifiers a/c and heaters etc are all needed to keep your humidity in check

[@natel9019]

I set the brain to lower the temp down ten degrees or shut off half off the room 10 to 15 minutes before the lights go off. To lower the temperature of the room so less water falls out of the air when the temp goes down. When I run big light depos greenhouses that is one of the things I make sure, that the greenhouse closes slow. 10 minutes or slower and when we do it by hand we do half at a time wait a while and then finish. Otherwise it basically can "rain" on your plants

[@Vanpotheosis]

So, when she says "VPD is low", doesn't it mean "VP" is high?...

[@surronzak8154]

The deficit of pression is low means the plant transpire less

[@samburgner8179]

Or leaf temperature is low

[@surronzak8154]

@@samburgner8179 not necessarely , you could have to mich light heating the leafs resulting in higher LST. I try to figure this out, i’m not in a battle ;-)

[@samburgner8179]

@@surronzak8154 I was commenting on the one above you sorry. If VPD is low, it could be a high vapor pressure outside the leaf or a low leaf temperature. Speaking from a calculating standpoint

[@patrey6797]

Yes When Vapor pressure is high the Evaporation Rate is low, When Vapor pressure is low the Evaporation Rate is high. So the Deficit Value gives you an indicator of the Evaporation Rate

[@47diodes]

"Do people know about VPD?" What kinda question is that? What amount of quality information can be derived from such an arbitrary question? Her response to that alone consumed 2.5 minutes of your video! Her response in a nutshell: Yeah sure, but lets educate 'em some more.

[@vpdmusic]

Hello! :D

[@IRailroad]

🤔

[@elliottbond6647]

0.50 literally.... not really