Grow Room VPD in veg vs. bloom

[lunarman]

I have read multiple times that VPD is not as critical during flowering. Curious what peoples experiences are with that.

I run on average 70 degrees F and 50% RH which gives me a VPD of 1.25. I do this during veg because its what I can manage given my climate. I'm very happy with this during veg. Plants seem to love the cooler moister air. If I went any higher temp I'd have to run a lot of water thru a humidifier I have in the tent so I stick with this. I already go thru 6 of the 5 gallon jugs of RO water every week. I can't justify adding more H2O.

But what about flower? Should I try and maintain the same FPD? Or can I drift off it during flower? I am wondering if I can reduce my RH to like 40% and save on bottled RO water expense during flower.

 

[MedCzech]

40 % is pushing it a bit low. 45 would be ok at that temp. Anything less than that would really add too much stress to the trichime production and that last push in weeks 5 to 8 of flower they need enough moisture to still grow and put in some mass.
Just lay some wet towels down on the floor of the grow space and you will see some gains in your RH numbers. No investment needed

Good luck and good growing!

 

[pop22]

Considering the expense of RO/Distilled water, you can get an RO filter for as little as $50. I paid $79 for the one I use now and can easily make 30-40 gallons a day! I saved some ice tea plastic jugs, enough to store ten gallons of water

I have read multiple times that VPD is not as critical during flowering. Curious what peoples experiences are with that.

I run on average 70 degrees F and 50% RH which gives me a VPD of 1.25. I do this during veg because its what I can manage given my climate. I'm very happy with this during veg. Plants seem to love the cooler moister air. If I went any higher temp I'd have to run a lot of water thru a humidifier I have in the tent so I stick with this. I already go thru 6 of the 5 gallon jugs of RO water every week. I can't justify adding more H2O.

But what about flower? Should I try and maintain the same FPD? Or can I drift off it during flower? I am wondering if I can reduce my RH to like 40% and save on bottled RO water expense during flower.

 

[lunarman]

Considering the expense of RO/Distilled water, you can get an RO filter for as little as $50. I paid $79 for the one I use now and can easily make 30-40 gallons a day! I saved some ice tea plastic jugs, enough to store ten gallons of water

I should look in to that.

 

[okPeet]

Here's a good series on VPD by Quest Dehumidifiers:
http://www.questclimate.com/vapor-pressure-deficit-indoor-growing-part-1-vpd/
http://www.questclimate.com/vapor-pressure-deficit-indoor-growing-part-2-vpd-important/
https://www.questclimate.com/vapor-pressure-deficit-indoor-growing-part-3-different-stages-vpd/

Part 3 talks about suggested VPD in different stages of growth.

 

[okPeet]

Also, check out this guide I wrote. https://getpulse.co/blog/vpd

 

[Simplicio]

An easier way to use VPD. Subtract 5-7 F from air temp to get leaf temp, and stay in the green.

 

[lunarman]

Considering the expense of RO/Distilled water, you can get an RO filter for as little as $50. I paid $79 for the one I use now and can easily make 30-40 gallons a day! I saved some ice tea plastic jugs, enough to store ten gallons of water

I did get the RO Buddie. Cost me more like $100 Cnd for the 4 stage one. But what a great investment. Paid for itself quickly and I don't have to drive to get bottled RO water now. Thanks for that recommendation.

 

[lunarman]

An easier way to use VPD. Subtract 5-7 F from air temp to get leaf temp, and stay in the green.

I use an infrared thermometer to check leaf temp, but it is pretty much always 5-7F lower. I've made a few improvements in my growing lately so its hard to pinpoint what improvements came from what change, but after two grows of following VPD I'm sold on it. I put good use to a humidifier in veg and a dehumidifier in flower in order to do it right.

 

[pop22]

I was hauling 20 gallons of commercially filtered water a week and said screw that lol!

I did get the RO Buddie. Cost me more like $100 Cnd for the 4 stage one. But what a great investment. Paid for itself quickly and I don't have to drive to get bottled RO water now. Thanks for that recommendation.