This is my indoor grow VPD, is my humidity too low?

I’m about to finish my first open air indoor grow in a 10’x10’x8’ room. I’ve changed a lot of environmental things during the grow but I want to improve.

Looking at the VPD chart I found here on ILGM, how important is it to stay in that green range?

With my 4’x4’ trellis net, using a 1000 watt HPS, I was consistently more under the green range than what I circled on the below image. After adding a space heater and 6 gallon humidifier, I got closer to the green range and that is what I circled.

It is winter, and I plan on only growing in winter next year. Is the range I circled acceptable for an indoor grow? I did have one plant of the four get airy buds (though it was an autoflower), while the two photoperiod sativas have very dense buds.

My canopy SCROG temps range from 64 F to 84 F with RH ranging from 22% to 52% *(sensor it at the top of the tallest cola of the SCROG). The room ranges from 60 F to 82F with RH ranging from 20% to 62% (differnt sensor near the door of the open room).

VPD chart is canopy ranges from a sensor that records a 24 hour time period.

Any thoughts? :thinking: :thinking: :thinking:

Canopy VPD

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Hey @spacey looks like you are heading in the direction I’ve taken this past year. Since the temps are so high in the summer I’ve elected to only grow from late September through mid-April.
In response to your VPD question about keeping the VPD in the green range. I only worry about that much humidity early in my grow. Once I get transitioning to flower I trend more toward the dryer range. I do not use any foiler sprays unless needed for pest after seedlings take off. I want to avoid any chance of getting bud rot or any other ailments due to high humidity.
Here’s a VPD calculator that is nice to use as a reference.

Good luck :four_leaf_clover:


I’d take those ranges for sure.

There’s an art to it though that I don’t think is expressed in that chart. You might fall outside of ideal range for vegetative growth by running on the dry side in flower, but the trikes are part of the secondary metabolic processes anyway and made in part to deal with drought stress. Also it forces the plant to pull up more water from its roots so you can pump more nutrients in.


Hello all, during my (1st) grow I kept RH 40-45% and temps 80-84F with my LVPD Avg above 2. Needless to say this is my first grow and I had lots of problems but I honestly feel that having such a high VPD was my No.1 issue that lead to such a poor harvest. I caught on to this about a month ago and adjusted environmental averages to 75-78F and 50-55%RH, but the damage is done.: Wicked bad Nute Burn, thin light leaves and low trichome density.

Does anyone know of a good book, video or read that covers, specifically Advanced Autoflower Growing?

@spacey, A couple tips here. I use this chart for transpiration rates or VPD. This chart cover the plants through their three stages of growth.

Also be very careful where you place your temperature/humidity sensor. A temperature sensor in direct light will read high. Try to place your sensors in the shadows or in the exhaust air to get a truer reading. Here is a picture mine hanging down in the plant itself. The sensor is hanging on the chain you see in the picture.

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I’m finding that just going by charts can be confusing, as they differ if they are slewed for a particular leaf temperature differential.

For lights-on, I’ve been going off of my max canopy air temp (85f), hottest leaf temp (80f), canopy humidity at time of measurement, & plugging all of that into the Dimlux calculator to get my hottest leaf VPD, & then I use that number to decide if I need to try & move the humidity, & the rest of the box follows behind.

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