In need of some help from this knowledgeable community! I’ve got a really high VPD according to my VIVOSUN probe and I can’t get it lowered.
Temp inside tent: 82-83*
Humidity 48-50%
VPD 1.8-2.2
27”x27”x63” grow tent. Oscillating fan full speed, inline exhaust full speed, light at 80% intensity (built in fan full speed) 23” above single grandaddy purp plant in veg (almost 8 weeks old). Floor vents open. Good airflow indicated by sides of tent itself being sucked inwards.
Tent is in garage. I live in SoCal and currently experiencing hotter than normal temps so can’t lower temp (no AC and not really looking to add), trying to boost humidity to lower VPD, but when I put a humidifier inside the tent full blast (about 2 hrs ago), it actually raised the VPD a bit (but is fluctuating).
I’ve got a secondary temp/humidity gauge inside tent and getting roughly same numbers as probe +/- 3
Also just did a flush, so soil is moist. Using fabric pots.
Any help or advice much appreciated. Temps should be back into upper 70s early next week and plan on keeping humidifier inside tent.
My light meter arrives today in which case I’m hoping to lower intensity of light and lowering closer to plant to help with temp (Vivosun SE 150 not producing much heat)
I agree, this isn’t ridiculously out of line. You don’t really want to lower your lights on temp much, this is about where you’ll get ideal leaf surface temp. And it will be difficult to get rh up with all your fans wide open.
The most ideal thing to do would be to run large humidifier in your garage so the intake air rh would be higher. But this seems like a lot to do for a garage grow.
Okay, this is promising to hear. This is only my second plant and first in this tent. In doing research about growing, I got the impression VPD is a big deal for optimal plant cycles.
Thanks. Didn’t want to lower intensity on light, but thinking of what variables I can control for optimal environment. It didn’t fully occur to me that RH would be a challenge with SO much airflow combating high temps.
Yeah humidifying the garage for a single plant seems a bit much haha.
In my reply to Midwest Guy I mentioned this is only my second plant, and first in a tent (I’ve got a white widow currently in flower outdoors). In doing research about growing, I got impression VPD is really important for optimal plant cycles and started to get nervous.
The very top, tiny leaves were taco’ing, but I think it was bc my light was too close. I moved it up last night and plant appears to be happier
Stoked to hear this haha. In reading stuff across the internet it felt like the opposite; experienced growers were mainly using this. Good reminder to always get second opinions /toss questions out here.
Be careful what you read on the internet. It’s full of nonsense growing advice and gimmicks. Check here before implementing internet advice or advice from grow shop employees. The growers here have as a collective have many decades of experience and we are motivated by nothing more than wanting to see newer growers be successful.
VPD isn’t all that important so long as RH is good. The basics will carry you far and provide the best results. Stick to the basics for the best grows. VPD is not a metric that I consider to be all that significant versus the basics.
Vpd is important, but it’s more like important to not have too far out of line. And the difference between perfect conditions and good conditions is wide.
If you’re running a million dollar grow it’s reasonable to spend couple hundred thousand to get it right. For one plant in a garage it would probably take years to see the return on investment between good and perfect.
With those temps you would need 80% RH to hit 1.1. I fell down this hole and realized it is not easily attainable to acheive the sweet spot all the way through the grow and also depending on the season, the conditions in the house fluctuate from summer to winter and it will drive you nuts.
I usually top my plants twice. Maybe 3 times depending on how the plant is doing. I also top major side branches once.
I do no LST other than to trim as necessary to maintain good airflow within the plant’s canopy. The plant otherwise needs its leaves to be healthy, as the leaves use light to produce the sugars the plant needs to grow. As a plant matures you can take off up to the bottom 1/3 of a plant without impacting yield. It helps improve airflow.
You want to monitor & adjust your Leaf VPD instead of your Air/Room VPD.
VPD target numbers are Leaf VPD target numbers, not Air/Room VPD numbers.
You’ll want to measure your leaf temp, then plug the leaf temp & the surrounding air temp & the surrounding rh into a leaf vpd calculator or dynamic chart to get your leaf vpd.
Heres a dynamic VPD chart so you don’t have to worry about switching across different static vpd charts if/when your leaf temperature offset changes. Just plug in your leaf temp, air temp, & rh data accurately. Dynamic VPD chart
Leaf Temperature Offset equation is (Leaf Temperature - Air Temperature), & the Leaf Temperature Offset specifically determines what each static VPD chart looks like.
