Question about VPD chart

Hi everyone :muscle::muscle::muscle:
Hope you are all doing great!
I was checking a VPD chart and it says im in a “sweet spot” (26-29C° and 70-85% RH) …
I don’t own a dehumidifier, maybe at some point i will get one, but it’s not even a possibility right now.
So, according to the VPD chart, im just fine, but EVERYWHERE ELSE they tell you that you absolutely have to get the RH down to around 50% or even lower, for flower…

I’m 1 week into flower now…

So, what do you think?
I have good airflow, but my environment is just too humid naturally…

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This is where it hovers at canopy level with lights On

And this is about how it is when lights off…

Having lost battles against mold in this same room, im pretty nervous about mold…

Differences between the moldy run and this one:
Much better ventilation this round
No pests of any kind for this whole run(had black flies, spidermites and botrytis on before grows)
Much better lighting
Only 2 plants instead of 5 or 8, so, really less humid
Very extreme chlorine job on every corner of the room, the tent and the gear, also keeping it clean constantly
FILTERED INTAKE, i believe this is the one that got me so far without bugs

I’m no expert but bud rot isn’t something I would want to invite to my grow, even with good airflow humidity is still humidity. I personally would say invest in a dehumidifier as soon as you can…

Keep in mind bud rot can ruin a whole grow. Time wasted. Try Offer Up or Facebook marketplace for a cheap solution.


I know man, im pretty nervous…
I do know with confidence that my airflow improved drastically and maybe my experience with Rot was because some bugs coming from the unfiltered intake brought it with it…

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Bud/root Rot isn’t caused by a bug bringing it in, it’s caused by the humidity. Keeping bugs out is a must as well, so good on you for that one, but I just don’t think smacking the buds with airflow will do much in the long run if your still just smacking it with humidity.


Also, the structure of my plants isn’t anywhere near as dense as they were under blurples, so better airflow in the plants and buds im hoping

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That’s a possibility as well…
That’s why i wanted to know if its VPD or just bring the humidity down at all costs (wich also, at my Temps, would get my VPD way off the sweet spot)

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Don’t hold VPD to be the end all be all of a grow. Many here don’t even bother watching their humidity other than just making sure it isn’t high during flower and they grow some extremely bomb stuff.

I only just recently got a Humidifier for my tent, but was growing at 81f and 36% humidity for a long while. No issues caused by it what so ever.


For now, as i say, this is an experiment to see if VPD alone is reliable for cannabis…
I won’t be able to get a DH for this round, but i sure can stay within the recommended VPD…
Let’s hope ill be posting my harvest around here in a few months instead of a bunch of mold and immature flowers like last time

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Don’t worry about VPD, it’s over-rated, the potential down sides of higher humidity in flowering far out weigh any benefits. In flowering get your humidity as low as you can.

As @Dankloud said, bud rot is not caused by bugs, it’s caused by too high humidity, spores that can cause bud rot is all around us just waiting for that humidity to go up enough to attack those buds.

75-80RH in mid/late flowering is just inviting bud rot to ruin your harvest.


Yep, that’s what I’m thinking…
Thanks for the reply man…
I will be trying different DIY/super cheap methods to get the RH down on that room where the tent is…
So far, I’m thinking on getting big bags of coal and seal the room’s window completely except for the exhaust, so no “fresh jungle air” comes in all the time…
If anyone has ideas for a DIY dehumidifier, bring them on please!


Quick google:

The most popular DIY dehumidifier is the one that works the best—rock salt. Rock salt naturally absorbs moisture out of the air, making it a great choice to use as a dehumidifier.

To make a rock salt humidifier, you’ll need a large bag of rock salt (also sometimes referred to as sodium chloride) and two 5-gallon buckets. You should be able to find both at a hardware store.

Here’s how to make it:

  1. Drill several small holes in one of the buckets along the sides and the bottom.
  2. Put the bucket with the holes inside the other bucket.
  3. Fill the bucket all the way up to the top with rock salt.
  4. Place the bucket in the area of your home you’d like to dehumidify.
  5. The bucket will begin to collect water, and that water will drip through the holes of the inside bucket.
  6. The water will then collect inside the outer bucket, trapping excess moisture.
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Thanks very much man, im looking where to get rock salt around here :muscle::muscle:

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