Vpd (vapor Pressure Deficit) What It Means To My Plants

[seaslug]

Edit to #15: let's make that tap water 0.20 mS, 100ppm using the 0.5 conversion factor.

For the last week, I've been keeping the flower room door closed during lights on and it raised the RH a little. My fans cycle quite often and I just added 330 watts. I don't know if my new humidifier is going to be of much help but a swamp cooler is not a big investment ($110).

OK, so here is a reason not to put water into my flowering room's air: my exhaust duct runs about 24 feet through an uninsulated attic. It is 10" diameter, insulated R8 but I don't want condensation in that duct during cold weather.

 

[shemshemet]

The idea of VPD is real...it is true. Greenhouse growers, and nurseries realize that RH means nothing without a factor of temperature.

Where the cannabis scene is getting confused is probably the VPD limits that we are seeing on these charts. I have not found a chart that outlines correct VPD for any plant. Just the cannabis based ones (from just4growers.com...), with seemingly arbitrary limits, that show a much higher humidity than we are used to.

I think some work on the correct VPD range for cannabis should be done. If I had more fancy equipment to keep my temp/humidity exactly where it needs to be I would try to do it...

 

[seaslug]

My first impression of the Essick Air (what a name) 821000 humidifier is favorable except it has no blackout recovery, it stays off. This means I can't hook it up to a timer or a controller.

I didn't start it until 8:30 tonight, right where the RH lifts off the yellow horizontal line at the far right. This is my log from the last day and a half:

So it only shows the first hour of humidifier operation. The humidistat in the unit was set to 45% and the fan was on high. If the humidifier runs out of water, the fan slows to the lower speed.
The wick:

 

[Seamaiden]

My first impression of the Essick Air (what a name) 821000 humidifier is favorable except it has no blackout recovery, it stays off. This means I can't hook it up to a timer or a controller.

That's a problem, no? It would be a problem for me, even though we're on automatic back-up power.

 

[seaslug]

I figured there was only a 50/50 chance Essick included a capacitor that would hold the digital settings so I'm not too disappointed but this would be a deal breaker for many growers. It won't work with an external humidistat or Sentinal controller, etc.

Still happy with my unit as of noon. A half hour ago, the in/out room fans came on for the first time today. I watched the Essick hygrometer readout dive from 47 to 42 within about a minute and the humidifier fan turned on.

The 821 000 model just looks like it belongs in a grow room:

 

[seaslug]

The last 22.5 hours, settings remain at 45% and high speed fan:

Looks good to me--establishing a definite RH floor will be of help to my plants, I'm sure. The data doesn't show it but the room feels like it's better now for the leaf stomata.

 

[jumpincactus]

take the article with a grain of salt JC,notice the plants pictured in it are mostly water loving veggies lol.lettuce for example has a much higher value when its bloated with water and nice n green. im not gunna sit in here and argue with these guys as many do pretty darn good using higher rh to grow.ill just say its not as important as some at this site might have you believe.my plants are happy and my patients love the smoke and i havent seen 50% rh in any of my rooms since oh about august.even then ill fight to keep it down around 40%.this time of year im lucky to see 25% rh but the plants chug along,my 8 wk strains still finish in 8,big girls still get big :)
i cant speak on landrace sativas as i have none growing,but all these hybrids dont mind none ;)

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mary jane is a forgiving plant,but if i had to put a number on r/h and its importance in growing weed it would be way down the list .peace

Very Nice @sixstring Nice indeed. Like I said in my opening post I somehow am on board with a higher Rh but like you I struggle with low Rh in a very arid place. I guess all a man can do is the best he can with what he has got. :D

Thanks for all the feedback Farmer.

 

[sensicloud]

The idea of VPD is real...it is true. Greenhouse growers, and nurseries realize that RH means nothing without a factor of temperature.

Where the cannabis scene is getting confused is probably the VPD limits that we are seeing on these charts. I have not found a chart that outlines correct VPD for any plant. Just the cannabis based ones (from just4growers.com...), with seemingly arbitrary limits, that show a much higher humidity than we are used to.

I think some work on the correct VPD range for cannabis should be done. If I had more fancy equipment to keep my temp/humidity exactly where it needs to be I would try to do it...

To further add to your post, it should be noted that not only different plants will favor different VPD values, but also different strains within that plant variety will favor different VPD values as well. I think that is why we see a lot of success with a lot of different plants at a lot of different VPD ranges. awesome thread..

 

[nazarbattu]

To further add to your post, it should be noted that not only different plants will favor different VPD values, but also different strains within that plant variety will favor different VPD values as well. I think that is why we see a lot of success with a lot of different plants at a lot of different VPD ranges. awesome thread..

I agree.
Years ago when I charted and experimented with vpd and charts I came to the conclusion that vpd charts are crucial In locking in a dialed environments for specific phenos....so before I quit vpd charting I had color coded charts for each pheno with notes correlating to pudding test and I found a causal relationship between vpd and phenos to be precise and the causal relationship between vpd and cannabis to be very vague .....

For instance before vpd charts I bent over backwards attempting to "dial" in environment for specific strains and after vpd charts (now) I grow in seasonal vented environment that swings allover the place throughout the year.

Before vpd I grew clone onlies attempting to replicate native environment now I grow from seed and the plants that flourish in a changing inconsistent environment "not dialed" stick around.....hope this observation is as relevant as relative humidity and leaf tempature.
nas

 

[DOGBUDS]

I dont need to read this to tell you to rock 70-85% humidity with 80 degree temps and co2 1000-1100 ppm. Ive seen the growth before my own.eyes. we run sealed with equipment to extract or add humidity so its ALWAYS perfect. That temp and humidity is used until end of.week 4 then down to 50-60% humidity and 75 degree temps. That is the secret recipe thanks @JACKMAYOFFER

Hey MWD, what is your Co2 regiment after week 4? Thanks DB

 

[ziplock]

take the article with a grain of salt JC,notice the plants pictured in it are mostly water loving veggies lol.lettuce for example has a much higher value when its bloated with water and nice n green. im not gunna sit in here and argue with these guys as many do pretty darn good using higher rh to grow.ill just say its not as important as some at this site might have you believe.my plants are happy and my patients love the smoke and i havent seen 50% rh in any of my rooms since oh about august.even then ill fight to keep it down around 40%.this time of year im lucky to see 25% rh but the plants chug along,my 8 wk strains still finish in 8,big girls still get big :)
i cant speak on landrace sativas as i have none growing,but all these hybrids dont mind none ;)

View attachment 486369 View attachment 486370 View attachment 486355 View attachment 486356 View attachment 486359 View attachment 486368 View attachment 486371 View attachment 486376 View attachment 486377

mary jane is a forgiving plant,but if i had to put a number on r/h and its importance in growing weed it would be way down the list .peace

Nice pics, nice plants.

 

[whocares]

I dont need to read this to tell you to rock 70-85% humidity with 80 degree temps and co2 1000-1100 ppm. Ive seen the growth before my own.eyes. we run sealed with equipment to extract or add humidity so its ALWAYS perfect. That temp and humidity is used until end of.week 4 then down to 50-60% humidity and 75 degree temps. That is the secret recipe thanks @JACKMAYOFFER

Same go for the humidity at night as well?

 

[midwestdensies]

Means the same 24-7. Hence vpd. All the time. Google vpd chart. Simple science. Harder to apply. Need a ultra sonic fogger from mainlandmart.com get a buoy. Brute tote and small fan for a dope humidifier. Environment controller. And a nice AC. Deheuy needed usually later in flower @whocares

 

[whocares]

Means the same 24-7. Hence vpd. All the time. Google vpd chart. Simple science. Harder to apply. Need a ultra sonic fogger from mainlandmart.com get a buoy. Brute tote and small fan for a dope humidifier. Environment controller. And a nice AC. Deheuy needed usually later in flower @whocares

i just meant like at night for example im usually a few degrees cooler (80 day 76 at night.) Should it run a little lower humidity at night to keep my vpd the same.

 

[whocares]

And I'm sure your walls would turn moldy if you fan 80% humidity at night for very long.

 

[midwestdensies]

No they don't. It is how I get huge yields. Vpd means 24-7. Day night and every hour in between. Period. This is not new info and I'm not the only one doing so. Mainland mart ultrasonic humidifier. That is how it's done. Don't be scared of what you haven't tried

 

[midwestdensies]

I do this from dome tray until week 4 of flower

 

[basseye]

I do this from dome tray until week 4 of flower

what do you do after week 4 flower?seems like thats when all the real weight happens no?

 

[midwestdensies]

The onset is sooner. The stomata is open when in that range. Meaning faster growth so direct correlation to yield. After week 4 50-60% rh

 

[DemonTrich]

I run a 12 disc ultrasonic fogger system from houseofhydro.com. owner is a super stand up guy and backs all his products. Had an issue with a 10 discs power supply, hooked me up with a free 12 disk and power supply upgrade for free. I use their 80mm water proof fan, and bouey. I sourced my own 19 gal tote, soon to upgrade to a 20 gal slim barrel/drum setup. With my fan speed controller I can match my temps to my desired rh just about perfectly.

Cost for the 21 disc, float, fan, fan speed controller and 24 spare replacement diacs was about 250.00. The container and pvc parts, and air bubbler was another 20.00.