VPD....like learning how to walk again

[Bennyweed1]

So I thought, never mind, cross that shit out. I knew I had to create a new post for this.

It aint my work, it aint my thoughts, I didnt even know about it until three days ago. I've been growing for a good 6 years, and never even heard about it. It has probably been the root cause of so many issues I labeled something else, wasted money on trying to fix, misdiagnosed as pH, over fertilization, off gassing....you name it, now smack yourself right in the chops for doing what I did.

This shit is for realz. Vapor Pressure Deficit. Get some. Figure it out, read about it and learn how to walk again.

Read this and then tell me how you knew about it all along.
http://www.just4growers.com/stream/...-deficit-the-hidden-force-on-your-plants.aspx

 

[The Groff]

Wow !! Great find. Loved the read and makes perfect sense! I think I may plot the formula to an Excel sheet for quick guidance... I'll share when I get to it.

Now I really need a laser thermometer haha... (true).

Have you ever heard of Brix measuring using refractometers? Here is a quick tour and great quick explanation of grapesvines, but another great tool for a more in depth direct reading of your plants (and master your feeding regime).

http://www.youtube.com/watch?v=BytEY9suKyo

Couple that with VPD for a proper environmental control, I can only imagine the potential here!!

Very cool Bennyweed1, thanks for the share

 

[DHF]

Said this last night in another thread that environment is "finite" and un-moving , so dial it and reap the rewards....

Means waaaay more than slingin light at their ass.....I thought brix measurement with refractometers was limited to soil/organic grow , but ANY tool that ups yer game and ain`t hype or snake oil works for me....

Figurin out the difference is the trick.....Thanks for the link Benny.....Now get backta work....

Peace....DHF.........

 

[The Groff]

Not at all. Brix measures sugar content in the plant's sap (sap = plant "juice" inside). Its a direct measure of plant health and yield quality/potential.

 

[DHF]

Not at all. Brix measures sugar content in the plant's sap (sap = plant "juice" inside). Its a direct measure of plant health and yield quality/potential.

I`ve heard conflicting info on chem based grows versus organic setups as far as the accuracy or comparison end of things Bro , so ....

Still don`t know as far as squeezing juice outta leaves grown with chem nutes compared to soil amendments , but as stated above I`m all for ANYTHING that helps growers up their game....

Brix measurement is not new , just mostly used in the organic indoor and outdoor setups that I`ve seen , but hey if it works on indoor chem based grows then all the better....anyways....

Peace....DHF.........

 

[budshoteyes]

This is new to me....I like it! Hope this thread grows! And I'll be watching it! Time to research the topics!

 

[The Groff]

I`ve heard conflicting info on chem based grows versus organic setups as far as the accuracy or comparison end of things Bro , so ....

Still don`t know as far as squeezing juice outta leaves grown with chem nutes compared to soil amendments , but as stated above I`m all for ANYTHING that helps growers up their game....

Brix measurement is not new , just mostly used in the organic indoor and outdoor setups that I`ve seen , but hey if it works on indoor chem based grows then all the better....anyways....

Peace....DHF.........

Good point! Will look into it

 

[The Groff]

Ok... I am officially confused.

First the read was confusing, then I got ti as it is dead simple. Except I started calculating my VPD and am now confused again.

Those 2 charts have the temp vs. RH% values in reverse to the second chart.
The first chart, the one that goes down to 35% and has the optimal VPD colored orange. That is derived from leaf VP minus air VP.

So to calculate your own you must use ONLY the second chart!! And you should never "look" at the first one to figure out how to compensate and stay withing optimal margins.

So that is what I am tryin to figure out... I could play around with numbers, but that doesnt work at all and confusing me even more

I dont have a laser thermometer, but usually leaf is -2 to -4ºC than ambient, so lets use -3 ... So in my tent

Air temp = 26ºC
RH% = 65%
Air VP = 21,8

Leaf VP = 23ºC @ 100% = 28,1

VPD = 28,1 - 21,8 = 6,3 (too humid, right?)

Great, I am almost in the perfect zone. I'm a bit off and want to get VPD 8,5.

Since I can't directly affect the leaf temp, I must control either air temp or air RH%. - to get 8,5 I need to increase VPD by either

a) increasing temps, therefore increasing leaf temp, therefore back to square one in terms of VPD calc. Not a bad thing though, you could fall into the optimal zone. But its too tricky-a-math for my brain.

b)maintain temps and decrease RH%... if I lower to

50% = VPD 11,3 = too dry
55% = VPD 9,6 = Excellent
60% = VPD 7,9 = too humid once more.

wow.. that is a tiiiight sweetspot.

The article is nice, but clearly badly written and exposed. One should never look at the first chart, it will only mess with your mind, unless I got it completely wrong.

Also, I've seen reference that VPD is expressed in kPa... but also these figures from this chart.

SO what I'm getting at is... the article is nice, and clearly will attract people to the blog, but IMHO fails to properly address the issue.

And since these margins are quite strict, we would need to be able to calculate, for instance, 53%.

Wikipedia freaked me out on this... anyone care to chime in ?

 

[butler]

New link

New link

The article in question has moved to here:

http://www.just4growers.com/stream/...-deficit-the-hidden-force-on-your-plants.aspx

Feel free to message the author through the site if you have any confusion.

Peace.

 

[PetFlora]

Thanks for this

It's one area I always mean to address but don't get around to

If RH is low, you can use inexpensive pond fogger and put it on a timer. Most likely you only want to run it ~ 15 minutes/1-3 hours. You have to monitor RH to see

Make sure to use water well below 300 as this level of ppms causes the ceramic discs to fail

I have 2 working foggers, but the discs are shot, and i have no back up discs

 

[hush]

This is a fantastic resource. Thank you Bennyweed (and butler!).

 

[PetFlora]

I looked more closely at my 2 tents

LED

temp 85
RH 50

hot5

temp 84 (but I turn ac on ~ 82 then off at ~ 75). Do this 5-6 times each day
RH ~ 45

The led plants are bushier with tighter nodes, BUT they re different pheno- expressing more Indica than in the hot5, which is expressing more sat

 

[Rolldaddy]

Thanks for this

It's one area I always mean to address but don't get around to

If RH is low, you can use inexpensive pond fogger and put it on a timer. Most likely you only want to run it ~ 15 minutes/1-3 hours. You have to monitor RH to see

Make sure to use water well below 300 as this level of ppms causes the ceramic discs to fail

I have 2 working foggers, but the discs are shot, and i have no back up discs

Can you post link or explain what type of foger you mean. I'm currently running several humidifiers and still having a tough time keeping humidity high enough. I've even been dumping water on the floor to increase it. And if your using foggers where do you spray it?

 

[PetFlora]

Can you post link or explain what type of foger you mean. I'm currently running several humidifiers and still having a tough time keeping humidity high enough. I've even been dumping water on the floor to increase it. And if your using foggers where do you spray it?

Just do a search for pond foggers. They come in 1/2/3/... heads to met any need

You probably would not run after light off so, leds don't matter

 

[catman]

Whole house wick humidifiers work well enough to make water leave from the inside-out of some leaves being they can already absorb enough moisture from others... in my experience anyway.