For you folks obsessed with humidity, some valuable information MUST READ!

[Gartner]

No one finds this information valuable at all?

Sure, Worthful and really valuable,
Mainly the Rh factor, I came to know from this article, as i am not aware of this,
Thanks for your posting...

:party0042:

 

[four20 bliss]

I love Maximum Yield. Great source of indoor growin info. I will be growing in a VERY humid climate so to know to check for VPD instead of only RH is very valuable to me. thanks

 

[Gartner]

Great information, everyone beginners to seniors, this is really helpful...

 

[TortureKill]

Great info!

 

[gooey]

good info, dealing with some humidity probs right now good to read up on more info....thanks for sharing

 

[stifler]

Gr8 post. rated

 

[dank_]

Essential information, thanks.

 

[ceaes]

great info thanks!

 

[Steel Erection]

Thanks for the article bro. My RH usually stays around 45-50% but lately its been dropping and I've been reading a few things that are making me want to boost it into the 60-65% range with my temps in the low to mid 80's. I'm gonna get a humidifier this week.Thanks again.-SE

 

[1dirtybastard]

whats the short version? OR quick answer.

 

[green guy]

I don't think you need a meter other than anything that can measure RH in the air and temperature. It is between those two values that VPD is calculated. I see you've found Autogrow's site.

This article in MY, as it's reprinted at least, is confusing to me upon perusal.
I found this to be simpler and easier to read, as well as overall more informative. They also have a calculator on their site, you just plug in the numbers.
http://www.autogrow.com/vpd_calc.php

The tables didn't copy properly, so go here to see the VPD tables:
http://www.autogrow.com/1_information/1_vpd/info_vpd.html

The bolded paragraphs are the salient points. The author of the MY article appears to have directly quoted Wikipedia (great writing technique, sheesh) without going much further into it. I found Autogrow's site easier to understand.

Thanks for your post. I added the autogrow calculator to my favorites list. And thanks to the OP, JimmyHoffa for the thread. I am growing in a generally low RH environment and this article opened my eyes. I thought I may need a dehumidifyer but may need to raise the humidity instead. One question I have is: Do the same rules and values apply to flower as veg?

PS I stumbled upon this thread doing a search on misting to see if I was over misting. Turns out I may need to mist more. Great site.

 

[Crysmatic]

i spoke to a drag racer the other weekend. water in the air affects power (and fueling calculations) and he told me he cares more about grains of water. it's an absolute measurement vs a relative measurement. we never want to cause condensation.

edit: that link doesn't work for me...however, I've had the equations for a long time. I googled 'how to calculate vpd', and this came up. it seems curing takes place at similar vpd. hth

 

[Crysmatic]

not to get too metaphysical, but i see plants as actively changing their environment to better suit them (same with fungus, maggots, humans etc). call it Terra forming. if the air is too dry, the plant sucks up water from the soil and releases vapour into the air. so if your plants are drinking tonnes of water, they're telling you to increase rH. while drinking less water, wouldn't ppm and pH fluctuate less?

if the air is too dry, the plant is hemorrhaging water, so it closes its stomata to stop the flow. i suppose at the high end, there's not enough differential to cause respiration.

i've also read that low rH does NOT increase the uptake of nutrients.

 

[ttystikk]

not to get too metaphysical, but i see plants as actively changing their environment to better suit them (same with fungus, maggots, humans etc). call it Terra forming. if the air is too dry, the plant sucks up water from the soil and releases vapour into the air. so if your plants are drinking tonnes of water, they're telling you to increase rH. while drinking less water, wouldn't ppm and pH fluctuate less?

if the air is too dry, the plant is hemorrhaging water, so it closes its stomata to stop the flow. i suppose at the high end, there's not enough differential to cause respiration.

i've also read that low rH does NOT increase the uptake of nutrients.

None of this is 'metaphysical'- it can actually be measured and quantified, unlike more fuzzy navelled concepts.

We humans prefer a certain VPD range too- ever notice when it's hot and dry, your skin itches and your lips chap? Or, when it's cold and damp, it feels clammy and uncomfortable?

If you raise your humidity to the optimal VPD levels- the single most useful part of that article to me was the chart, I have it tacked to the wall!- what you're doing is removing one more potential source of stress on the plant. If all else is in order, then you'll see your plants' growth rate accelerate.

I live in a very arid state- I've seen single digit relative humidity numbers- and I can say from personal experience that low rh is NOT the be-all end-all for great growth, far from it! That said, getting a decent environmental controller that will run your vents, humidifier and CO2 is a wise investment that will pay off big time. Don't sweat getting one that calculates VPD, just pick a good combo and set your controller to it. I like 75-78 for veg, with 60-65% relative humidity. For bloom, I go up to 80-82 degrees and stick with 60-65% rh which gives a somewhat 'low' vpd, but it seems to work for me. At the very end of flowering, I drop the humidity and let the plant dry out some, it tends to sweat out just a bit more THC that way...

BTW, it's a myth that these plants secrete THC resin to protect themselves from low humidity. They're doing it to attract male pollen... which if they don't get, they'll continue to get more and more hard up... which is what makes them so sexy!

 

[Seamaiden]

I know I'm happiest in an RH that's rather tropical, 70%+ (temps dependent, of course). :)

 

[ttystikk]

Bump. VPD has continues to play an important role in my garden, and has been responsible for how well my girls responded to co2 last round.

 

[rawman]

Been hip to VPD for awhile, since I bought my controller which actually measures your VPD

 

[L.Burna]

Great info... Have plants that do great in low humidities.. 20-30, anything over 40 percent rh and they start doing worse and may even develop PM!! Terrible because humidity is hard to control in the winter time especially where I'm at! Summer time is a whole lot better.

 

[caveman4.20]

VPD reminds me of a Torque Wrench it's a great tool if you apply it properly its a secret weapon, learning the specs is the tuff part... Because plants need different torque at different situations so VpD is even more complicated than the torque wrench with a manual giving you specific torque....this is another reason why Mono growing is desirable. Plant familiarity and pheno familiarity is the key. This is why I give advice to lock down environment first then get familiar with your phenos

 

[ttystikk]

Been hip to VPD for awhile, since I bought my controller which actually measures your VPD

Really? Can you tell us the model? What you paid? How well it's working out for you? I'm starting my search for a new grow controller and I'm interested in what you got.