VPD vs. PPM

Clutchcargo_1 said:

I agree. My formula might need some tweaking but I think you get my point in that the transpiration is a conveyor belt for nutes. The higher the humidity the slower the conveyor belt goes but the rate of nute consumption needs to be the same regardless of RH. The only lever that we have is to change the ppms to accommodate the changes in RH.

Click to expand...

That rings a bell.
After reading about VPD, I drank the Koolaid and decided to use a PulseGrow meter. There might be something about that in their blog or tech notes. If not, send an email to Pete. Very helpful and very knowledgeable.

I’ve had the same issue. 15-30% rh and couldn’t figure out what all my plants were super dark green and developed tip burn halfway through flower even though there was zero N in the mix for weeks.


using GH trio I can feed at basically seedling level for a 3-4oz plant. 400ppm max for a couple weeks during the height of flower and usually about 200ppm the rest of the time.