It’s difficult to look at singular VPD calculations. It swings a lot as T&H move around naturally. Compare the green squiggles to the black moving average. I’m not sure how you’d do this very well without a way to get average VPD values.
An increase in daytime humidity made my overworked dehumidifier happy, it ran about half as much. It also vented about half as much, which is really good for CO2 consumption.
The nighttime T&H similarly required less intervention (but lots of venting, which doesn’t bother me overnight as there isn’t any CO2 consumption).
Ambient basement conditions are RH=40, T=71F. I decreased the whole house humidity a few percent, this may have helped. It’s winter here, but not so cold out that <=40% RH is necessary, but the house is still comfortable.
What do you folks do? Anyone pay any attention to VPD? Anyone obsess about it like I have this week? Why do I feel like my charts are causing MEGO from you folks (“my eyes glazeth over”)?
This yields VPD between 1.2 and 1.5. This is higher than what you’d run normally, but with the CO2, and higher temperatures, that’s my plan. Non-CO2-supplemented grows should be between about 1.0 and 1.2 for flower, I think.
I’ve been supplementing CO2 for about a month, and the 20# tank continues to spit out CO2. An exchange is ~$40? Hopefully I can get through the whole grow with just one exchange (it’s still running on the original 20# tank which was only partially full when I acquired it).
There’s no way I could do this in the setup I had previously (a panda film-draped off room). I don’t think my cheap tent is as well built as a nice Gorilla or something, but it seems to be airtight enough. I wish I had more height, though.
Thanks for sharing the articles. I haven’t used CO2 in my grows. Well, except that time my gas water heater (in the grow room) exhaust came off all fixed now. I love my lights but its not enough light to make using co2 worth the effort. I had put some thought into it. Maybe in the future i would use it but for now, keeping my VPD in range would help the girls. Great subject .
Well, ok. But CO2 just changes my VPD target range. It’s the same hassle to adjust things to get VPD in-range. Without CO2, in flower, I think you want 0.96-1.2. Im just higher at 1.2-1.5.
Sorry if i misworded, I was referring to the money and effort it would take for me in my personal situation to add CO2. Especially with my vpd frequently going to high. I agree CO2 is beneficial to the indoor plants when light levels are proper and vpd in range. The science article showed an increase in biomass with low vpd and high CO2. Something we all want. CO2 is just not for me right now in my basement grow.
I was trying to answer your question. Sorry if I offended in any way friend
It is hard getting it in range. Then the seasons change on me and I’m back to dialing it in again
I noticed the RH in my whole house was low, 28% making it even harder to get my tent rh up a little. Yesterday I cleaned the while house humidifier in the furnace and replaced the filter panel. Brought my house rh up to 43% Hopefully that will help the tent RH. Its always something messing with my vpd
I had to decrease my house humidity a bit (45 to 40%), but part of that is how cold it is outside.
On the other hand, I adjusted my nighttime humidity a tiny bit (50 to 51%) at the time shown with the arrow. It decreased my VPD from 1.5 to 1.35ish. Tiny adjustments make a difference.
I’m in the middle of the 3rd week of 12/12. My nutes schedule (below) calls for 950-1200 PPM (500 scale), and it seems to drop quickly in the res.
In 24h, the PPM dropped from 1130 to 910. The previous day had a similar drop, and I supplemented with nutes for ~5gal, which brought it up to ~1110. This morning, it’s at 940 again.
Should I continue to add nutes? It’s been several days in a row that I’ve had to add a bunch of nutrients…
Help?!
(ps: I haven’t reached Late Bloom yet, but “Ripen” is Dry Kool Bloom)
And I’m watching. And learning. 
. (See above, CO2).
all fixed now. I love my lights but its not enough light to make using co2 worth the effort. I had put some thought into it. Maybe in the future i would use it but for now, keeping my VPD in range would help the girls. Great subject . 
