Night time VPD

Hi. My environment is pretty moderate and was thinking of saving some water in my humidifier during night time, allowing my night time VPD to drift a little. Is this advisable?

There are people that say no but I have done this in multiple places around the US and have had no issues at all except 1 time in each place I overfill the storage container. Keep fans ac units and dehumidifiers clean also reservoirs. Using your runoff will definitely has a different ph than the water your using ph keep that in mind . Dont pre adjust runoff it’s a waist of time .just know your ph will be different in your nutrient solution dont need adjust twice. I have well over 20 years experience 8 of those years where large scale commercial experience running facilities with over 200 lights. I also ran a couple of hydro store for almost 12 years. Hope that the cleaner you keep you spot clean the likely you will have problems.

Night time VPD doesn’t really matter anywhere near as much as daytime, so do what keeps your plants healthy & happy, and whatever is convenient for you.

Some research I did (specifically on nighttime transpiration):

According to the best of my research the difference between day & night transpiration is pretty big. See the figures and referenced studies below. Where did you arrive at your numbers?


From Tang, K., Fracasso, A., Struik, P. C., Yin, X., & Amaducci, S. (2018). Water- and Nitrogen-Use Efficiencies of Hemp (Cannabis sativa L.) Based on Whole-Canopy Measurements and Modeling. Frontiers in Plant Science, 9. doi:10.3389/fpls.2018.00951


From Medrano, H., Tomás, M., Martorell, S., Flexas, J., Hernández, E., Rosselló, J., … Bota, J. (2015). From leaf to whole-plant water use efficiency (WUE) in complex canopies: Limitations of leaf WUE as a selection target. The Crop Journal, 3(3), 220–228. doi:10.1016/j.cj.2015.04.002

From ESCALONA, J. M., TOMÀS, M., MARTORELL, S., MEDRANO, H., RIBAS-CARBO, M., & FLEXAS, J. (2012). Carbon balance in grapevines under different soil water supply: importance of whole plant respiration. Australian Journal of Grape and Wine Research, 18(3), 308–318. doi:10.1111/j.1755-0238.2012.00193.x

Pictures aren’t loading, but thanks for the info. Yah will experiment with putting the humidifier on the same timer as my lights and see what it looks like.

Pics should be fixed.