Tent Parameter (humidity & temp)

Hey guys,

I’m currently on the day of the switch to flowering and want some of your input on one slight issue I have.

Last grow I had a bunch of issues due to mold growing in the buds I presume due to high humidity and now enough airflow.

So this is the dilemma, I live in a quite humid country averaging 80% on a daily basis, and in my tent averaging 65% on a daily basis and I wish to keep it at 45% constant.

This is the problem I have, if I turn on the intake fan (outside air) the humidity will always be high in the range of 75% so I turn it off during flowering and only have the extractor running (it’s running 24/7 from the beginning of the grow) , if I turn on the dehumidifier it will help goes down to 60% but heat will go up since its the byproduct of the unit, I also have a portable a/c unit bought specifically for the plants but still the humidity refuses to go below 55%.

Currently I have 2 fans running on full speed to keep the air circulating, I DEFINETLY don’t want to deal with mold again in this one as I lost a lot of buds due to my stupid mistakes.

Are there some options which helped you keep the humidity as low as possible?

Here are some photos of my grow, 60 days old white Widow and Blue Dream (my favorite strains) running in dwc, complete GH nutes and 2 sf-4000’s on 75% power




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Nice nets

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Hello and welcome.
When I defoliated my plants at day 21 of flower it made a descent change in my humidity.
Where you thinking of doing a light defoliation?
Do you have good suction when your exhaust fan is on?

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Dehumidifier outside of tent?

You shouldn’t need it below 55% RH even in flower.

If you are under 65% consistently and still getting mold you should consider your environment and how those spores are getting in there. You might need a deep clean and HEPA intake filters if you can’t keep mold out and are under 65%RH

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Airflow is your friend in flower. Above. Below. Fans. Oscillate boom problem solved. And proper rh in flower is a must.

Light defoliation was already done twice and yes I do have suction all the time since fan is on 24/7

yes no space for it in the tent and heat would build up much quickly

Mold happens mostly due to high humidity and not enough airflow, no I added more airflow and want to find a solution to humidity

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Yep, I added a fan to anywhere where there is not enough airflow, what would you think best rh would be? In winter I manage to keep it constant 45 which is great but in summer times slightly harder

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Outside tent not inside. You would suck in humid air with it inside. You want the larger room brought down. Only way is dehumidifier

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I ignore rh unless it’s high in flower. Only because I vent to outside so keeping rh stable is impossible for me. Until harvest I stop venting to outside and set for drying.

So best to ask others on RH

Got an infared thermometer? If you can measure the leaf temperature and subtract it from room/tent temps taken on average. Then match that number to the top left corner of these charts (how you know which one to use) you’ll be golden.







These not only tell you acceptable conditions. But also are part of “optimum growth”. For when you get to the stage where you “dial in”. Most will require a dehumidifier. Ignore sq ft and other descriptors of dehumidifiers. Get a 30 pints and get it over with. The 30pt is how much it can remove in one day. I use one and it removes almost 4qt a day, maintaining my Rh easily. You want to go higher because that 30pt is under specific conditions. Anything less than 30pt is gonna basically stop working when you want to go under 55/60%. Which you do.

Thats actually something pretty new to me, never heard of leaf vpd.

Well after measuring it out, I’m in the sweet spot for humidity

Leaf temp is between 24.7°c and 25.3°c so took an average of 25°c & room temp is 27°c so a difference of 2°c, if I understood the chart correctly optimal humidity levels should be between 55-65% since it’s the first week of flowering.

That’s genius! Thanks Budz



Your thermometer needs to be almost touching leaf btw. I use the exact one. The infared sensor fans out. I take multiple leaf readings with mine almost touching the leaves. But you get the idea and that’s great. Bugbee does it better justice than me, of course.

And turn the laser off when using. Just a distraction and useless radiation, unless you’re cooking. Close up the red dot is not what you are reading. Not close up you can’t read the leaves.