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Eugene,OR

It is hard to read the numbers on this chart (at least on my phone), but what it shows is how much more humidity is necessary to sustain optimal growth as temperatures increase. I will attempt to maintain a VPD between 1.0 & 1.2 each day for as long as possible. I believe this is the single biggest reason that my personal best has risen from 1997 to 2301 since I built a greenhouse. As I have learned from our cannabis growing brothers, environmental control is the key to growing any crop to its potential. It is ALL about environmental control.

[Last edit: 04/07/25 12:28:23 PM]

4/7/2025 12:25:11 PM

Roseville CA

So does this mean that having a misting system will also increase plant/leaf growth other than cooling your plant?

Also have you seen more desise pressure with more humidity?

4/7/2025 10:48:16 PM

Bethlehem CT

Vineman that is a great and simple explanation as to why a plant grows faster with higher temps. It is something I have always known, but never really understood why.

4/8/2025 8:33:00 AM

Eugene,OR

Sanklap, a misting system will keep your plant alive at higher temperatures, so yes it will help your plant grow faster.

4/8/2025 10:08:53 AM

Eugene,OR

Many of us have been taught that plants stop growing when temps reach between 85-90 degrees because their stoma close down (I’m assuming that this is to conserve the moisture that is in the leaves). However, if there is adequate moisture in the air they will continue to grow rapidly. Last year during the first 35 days of vegetative growth I was routinely running temperatures of 100 degrees. By maintaining a VPD of 1.1-1.2 at this temperature my plants thrived. After day 35 I found that it became much more difficult to maintain high temperatures without having leaf damage, so I quit running my greenhouse so hot at that point.

[Last edit: 04/08/25 10:26:30 AM]

4/8/2025 10:24:27 AM

Eugene,OR

Don’t be misled into thinking that by running hotter & maintaining the appropriate VPD that you have the answer to the age old question of “How do you grow the world’s biggest pumpkin?” This is just one piece of the puzzle that most of us haven’t been taking full advantage of. It is simply an attempt to get a little bit closer to the best possible end result.

4/8/2025 12:10:14 PM

Mill Bay, British Columbia

So, the outdoor growers like myself have no control over this, or does overhead watering and misting help with VPD?

4/8/2025 12:46:32 PM

Eugene,OR

If you start in some sort of an enclosure, then you can take advantage of the opportunity to control your environment until you outgrow your enclosure. And yes, humidity/misting will help your plants keep growing when it is hot, rather than just shutting down until it cools off.

4/8/2025 11:49:53 PM

Vancouver, British Columbia, Canada

How do you control the relative humidity(the top line on the graph) in your greenhouse to maintain an optimum VPD of 1-1.2? Temperatures can be controlled via heaters. I often find my greenhouse is very humid and have placed a small dehumidifier to keep the RH at about 50-60%. I live in Vancouver where the outside RH is quite high. Thanks

4/10/2025 1:59:24 AM

Lloydminster/AB

I found that chart on our provincial Agriculture site under greenhouse growing. The next year my weight went up 300lbs.
I vent during the day and our air can be really dry. Required a lot more water than I thought.
If the temp gets as high as it is here it’s almost impossible to get too much humidity. Of course we don't have to worry about disease until the spores blow in from down South where it overwinters.

4/11/2025 12:18:46 AM