VPD vs. High Humidity

Hey all,
I’m currently in flowering, and I always have to deal with higher-than-I-like humidity, but my VPD is nice. For example, looking at my logs from yesterday, my average temp was 79 and my average RH was 69, with an average VPD of 1.1, which I’m pleased with.

I have wrestled with the humidity, and I just have to deal with it. I tried a dehumidifier but that creates enough heat to bring my temps up past where I like. Just rolling with it.

Anyways, I guess my question is which is preferred – shooting for a good VPD even if that means going higher/lower on temp/RH or trying to maintain proper temp/RH even if that means the VPD will be higher/lower than what’s needed at that growth stage? In other words, we see charts that show optimal temp and RH at different stages of growth, but is it better to stick with proper VPD?

My plants are not complaining and seem to like the environment, so that also tells me a lot as well.


I’m a bit new to this whole VPD concept. But generally, in my experience having RH on the high side during the first half of flower can boost your yield significantly, on the flip side, potential for PM is greater. It really comes down to your strains immune system and genetic resistance to PM. If both are high, boom bang booya. If either are weak, bum bum ba dum. Its science bro.


Makes sense. Right now, my plants are loving life, and I have a ton of air circulation to help prevent budrot. Ultimately, I guess that’s what it’s all about.

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I agree w/ @MeanMrMustard - if you can get away w/ the higher RH, go for it, but keep in mind that it is risky. Make sure your airflow is good and that you meticulously check your plants for any issues to catch them early.

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In the last few weeks of flower, I definitely aim to keep my RH on the low side – even if it breaks the rules of VPD. VPD is important for the uptake of nutrients, which your plant is not doing a lot of in the late stages of flower. Instead, it is ‘finishing off’ by spending all of it’s stored nutrients to ensure a successful ripening. This is also why plants change color at the end of bloom.

So in the final weeks, we are not as concerned with nutrient uptake as much as we are trying to avoid mold or bud rot.

TLDR: Keep the RH on the low side towards the end of flower.

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On that note, I actually try to get my RH as low as possible the last ten days. Below 30% if possible. Theory being, the plant is stress triggered onto producing more protective resin, aka cannabinoids.

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Thanks again, all, for the recommendations. I ended up putting my dehumidifier in the lung room today because the RH was just getting too high for my liking. These are autos in flower with about 30 days to go. I guess I was hesitant on putting this in place due to the current it draws (up to 700 watts) and the heat it produces. Now that it’s running, I don’t think the heat will actually be an issue because the house AC is equalizing that, but I may feel it some on the electricity bill. Oh well…cost of having a hobby…not to mention I need to keep in perspective the amount of money in the end I’m saving by growing my own.

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Oversize you dehumidifier it won’t run as hot.or even possibly a bigger ac unit

Wow my man you forgot the NSFW tag :sweat_smile:. Those plants are looking amazing.

Nutes might be running a little hot though

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first time runnin VPD and i’m nervous :grimacing: starting week 7 flower and i REALLY want to dump that humidity.
runnin 3x3x7 with 6” inline with 4 fans. only run 2 oscillating fans 24/7, opposite corners, 1 above canopy, 1 below canopy. both pointed at canopy.
1 i run for half day when i water/feed, it’s 10” up from floor pointed down.
the last 1 is backup.
i read some other posts and responses on this issue but still VERY nervous. i just lost a plant outside to mold… no good.
any feedback is GREATLY appreciated. thx

so close to finish line :grimacing:

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