I disagree with ya there. Your right on vpd outside why would you try outside lol. VPD can be used by growers indoors. Why wouldn't I want my plant to be in correct humidity and temp so that the plant improves uptake and transpiration etc. When I combine vpd and dwc it is a hell of a growth rate,nothing like a slug in soil lol. Knock on wood I have not had mold etc while doing this. No matter how big the flowers are.  Have a good one Vince