VPD vs "80-85°F"

shimbob

shimbob

Well-Known Member
The general rule of thumb everybody repeats concerning running LEDs and accounting for the lack of UV seems to be that the air temp should be warmer, around 80-85°F. But how does this jive with maintaining proper VPD? Shouldn't the VPD override this rule of thumb? Is it more important to raise the temp compared to getting the VPD dialed in?

In our current grow, if I kept temps at 83, that would put VPD at 1.3kPa, too high for the current stage (early flower). I'd have to bring humidity up to 60% to lower VPD, inviting problems with mold. I hate mold.
 
CobKits

CobKits

Well-Known Member
i think the overall health of your plants takes precedence over metabolism. you can still raise healthy plants at lower temps with some tweaking, but mold puts your whole crop in the garbage

winter is a bitch with LEDs sometimes ive actually run a small dehuey *inside* my tent to keep the temp and humidity in the right place with the tent exhausting on temp control
 
Humple

Humple

Well-Known Member
shimbob said:
The general rule of thumb everybody repeats concerning running LEDs and accounting for the lack of UV seems to be that the air temp should be warmer, around 80-85°F. But how does this jive with maintaining proper VPD? Shouldn't the VPD override this rule of thumb? Is it more important to raise the temp compared to getting the VPD dialed in?

In our current grow, if I kept temps at 83, that would put VPD at 1.3kPa, too high for the current stage (early flower). I'd have to bring humidity up to 60% to lower VPD, inviting problems with mold. I hate mold.
Click to expand...
Good topic. I'm very interested in this myself. I've definitely seen a huge leap in the health of my plants, over the life of the grow, by getting temps up over 80°F and humidity around 60%. BUT, I did have mold issues by the end of flower in my last run, and lost too much bud because of it. I've been wondering what impact the growing method (soil, coco, hydro, organic, synthetic, etc.) has on people's ability to run lower temps under LED. I've been a ROLS grower from the beginning, but I'm about to start a hempy/Mega Crop run, and I'm not going to make an effort to keep the temps over 80° - at least to begin with. We'll see what happens.
 
shimbob

shimbob

Well-Known Member
CobKits said:
sometimes ive actually run a small dehuey *inside* my tent to keep the temp and humidity in the right place with the tent exhausting on temp control
Click to expand...
This is where we're at now, dehum inside the tent. Also have a small spaceheater connected to a day/night temp controller.
Right now, in a tent with 670-ish watts of Q strips, air temp is 21C, leaf temp is 22, and RH is 53%. That's a VPD of 1.32. I'd rather it be 1.0, which means either raising RH to 66% or dropping temperature to 16.5, or a combination of the two. Getting the temp up to 80F would require a RH of 78%, no way that's happening.
 
Chip Green

Chip Green

Well-Known Member
This is something that would behoove me to start working on with greater effort.
Maintaining conditions is challenging in my areas. Yoop MI basement, VPD all over the place as the seasons swing.
Ive been kinda getting away without really paying enough attention to proper VPD, all the while missing out on opportunity.
 
Humple

Humple

Well-Known Member
Chip Green said:
This is something that would behoove me to start working on with greater effort.
Maintaining conditions is challenging in my areas. Yoop MI basement, VPD all over the place as the seasons swing.
Ive been kinda getting away without really paying enough attention to proper VPD, all the while missing out on opportunity.
Click to expand...
Michigan grower in an unfinished basement here too. Environment is my constant enemy. Someday I'll build an insulated room down there, with climate control galore, but for now, the struggle continues...
 
OLD MOTHER SATIVA

OLD MOTHER SATIVA

Well-Known Member
Humple said:
Good topic. I'm very interested in this myself. I've definitely seen a huge leap in the health of my plants, over the life of the grow, by getting temps up over 80°F and humidity around 60%. BUT, I did have mold issues by the end of flower in my last run, and lost too much bud because of it. I've been wondering what impact the growing method (soil, coco, hydro, organic, synthetic, etc.) has on people's ability to run lower temps under LED. I've been a ROLS grower from the beginning, but I'm about to start a hempy/Mega Crop run, and I'm not going to make an effort to keep the temps over 80° - at least to begin with. We'll see what happens.
Click to expand...

I'm not going to make an effort to keep the temps over 80°

>change anything/everything on your list EXCEPT this [and get some good air movement]
 
InTheValley

InTheValley

Well-Known Member
Humple said:
Good topic. I'm very interested in this myself. I've definitely seen a huge leap in the health of my plants, over the life of the grow, by getting temps up over 80°F and humidity around 60%. BUT, I did have mold issues by the end of flower in my last run, and lost too much bud because of it. I've been wondering what impact the growing method (soil, coco, hydro, organic, synthetic, etc.) has on people's ability to run lower temps under LED. I've been a ROLS grower from the beginning, but I'm about to start a hempy/Mega Crop run, and I'm not going to make an effort to keep the temps over 80° - at least to begin with. We'll see what happens.
Click to expand...
the trick is to lower the humidity at lights out. They dont need the humidity at night, just like the CO2. 1-2 hours before lights out, is when you need to dry the air, which will dry the leafs of any moisture, thus reducing the chance of mold. I lost a shit load to ( 90g) because of it, and my last run so far has been great regarding .

Ive tryed to target the VPD, but my plants dont like it. They do best at 81F and 51% humidity. ( prayin leafs) When i get it up to 65%, they dont pray.
 
Chip Green

Chip Green

Well-Known Member
Humple said:
Environment is my constant enemy
Click to expand...
Yeah I have, I'd say, mediocre control over the climate in the rooms, but the outside ambient conditions really play into the balancing act....The transition months especially. In the dead of winter its actually easier, when the furnace is predictable.....
I've had some pretty remarkable harvests, with conditions that were downright appalling , well , "on paper" at least ….
I VEG in shockingly low RH....
Its the results that matter, not what is "required", but I could stand some improvement.
 
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