CannaGrow Fastbuds #2 2024

1.2-1.6 is fine.. this is based on atmospheric temperature readings? VPD is supposed to be calculated with leaf temperature readings (averaged throughout canopy). So, leaf temps are about 3-5F cooler than the air due to evaporation that takes place (an endothermic reaction that absorbs heat from local environment). You vpd is lower than what you atmospheric temp caclulations are. Make sure atmospheric temp -5F is not less than 1 kPa on the VPD reference table. In flower some suggestions i;ve seen are anywhere from 1.2-1.5 anyway. And, you shouldn't have more than a 0.4 swing from day to night, if possible. Stomata are mostly closed at night, but if you can avoid big deviations, do so. There will be am optimal vpd in regard to maximizing co2 intake, but without a lab, that's pretty hard to dial in. So, if vpd gets a bit high and you cannot do much about it, be prepared to reduce overall concentration of your fertilization, if needed. High vpd means an increased rate of drinking... which will increase the supply of building blocks given while growth remains relatively the same = potential for tox buildup in the plant, all other factors remaining the same. Low vpd may require a higher concnetration. These two factors are linked in this way many other relative factors. if you don't tightly control climate, don't worry about things you cannot control. Use it to ensure you avoid extremes as best you can given the tools you have or choose to use. For instance, to help temps and rh in winter, i sometimes have a fan blowing cold air toward the thermostat. It can raise the temps ~3F or more and reduce RH 1-3% or more due to furnace turning on more*. I just try to avoid the extremes, but i still keep track of vpd. it can help inform on choosing a course of action for a toxicity or deficiency.. due to the direct correlations spoken of above. *it's a tri level with thermostat on top level. This works better than changing the dial on thermostate because it more evenly distributes the heat in the house at each level. Otherwise the mid level gets really cold and top level gets really hot, while the lowest floor is barely impacted. A little wireless temp/rh probe that monitores this stuff constantly is well worth the ~10 usd cost. Do remember the VPD shown on these probes is likely lower than the calculation given. A "good" one might allow you to choose an offset to use. - 3-5F is wise.