Help, humidity ranging 70-80°

If you put a baking sheet (or whatever will fit) of charcoal in the tent, uncovered, it’ll do wonders. It will need to be changed frequently though, just monitor the %


Are you talking about regular charcoal briquets or lump charcoal work as good or better?

I actually think the briquettes are more porous, and the cheaper the better. Those “good” ones that burn for a long tome are denser…

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Opened can of charcoal last night and humidity went down to 70°. Tonight I’ll place on sheet and dehumidifier is supposed to come today. Keeping fingers crossed!

Thanks @Whodat66! We are in the the first week 12/12 with the lights and the temp/humidity has been at 77/53. Thinking that humidity should be in the 40s.


I’ll let you know what happens with mine. We’ve had a rainy humid Sumner her & I’ve fought ever since flowering but this last week couldn’t get below 70° so ordered dehumidifier and using charcoal for now it’s dropped to 60s per cent

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Got dehumidifier today. Already put in tent while girls are sleeping. It has a green light that I covered up for fear of any light. They get up @ 8pm so then I’ll have a better idea.

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Feed girls & humidity is down to 69% and Reservoir already had almost a qtr inch of water. I’ll check again & see if it’s come down anymore. Thanks to everyone for the help.
Freaking bad as I’m in end of week 7 flowering.

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More Circulating fans may help with keeping bud rot out… (not sure how many you have)

If your flowering a bunch of plants, try staggering your watering… all that watering at one time may be driving up your humidity. What is the humidity outside your tent, like in another room in the house? If smell isn’t an issue open them tents up :slight_smile:

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I actually found the charcoal trick after a hurricane that knocked out power. Long story short, ever smell a freezer that has thawed? A few weeks of rotating charcoal (and gagging) had if useable again. Bleach and stuff too, but the charcoal did wonders.


My humidity doesn’t always go down with tent open. Not sure but think it maybe due to dewpoint has stayed over 70% for two months. I’m in a state that normally doesn’t have rain from July to end of October but this year it’s rained hard two days at least every week. Also due to heat issues (heat index 110°) lights come on at 8pm off at 8 am & they’re in my bedroom. Before I got the cool tube the room was like trying to sleep in jail due to light and having vents open

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Anyone have any suggestions: last two weeks of flowering humidity zoomed into 80+%. Have pan of charcoal, dehumidifier, exhaust fan, 260cfl fan & 2 6" fans running on high all the time and can’t get humidity down past 64%. Anything else I can do? @bob31, @Countryboyjvd1971, @garrigan62


Here is your answer…hope it helps If you can keep it where it is you’ll be ok

Optimal Humidity:

60 - 70% rH for vegetative growth.

40 - 60% rH during flowering (lower rH helps to reduce the risk of fungal contamination on your already moist dank buds).

80 - 90% rH for rooting clones and cuttings (high humidity is a must as these new plants may not have roots to draw moisture through).

More Details and Commentary:

Night temperatures should be kept above 60 degrees to prevent stress. It is preferable during flowering to have a night temperature drop of 10-20 degrees to stimulate flowering hormones and reduce stem elongation.

If you are supplementing your grow space with additional carbon dioxide (CO2), your target daytime temperature should be between 80 - 90 degrees (F), until the last two weeks of flowering when daytime temps should be kept about 10 degrees lower and CO2 can be reduced to adjust for the lower metabolic rate of the mature plant.

While one should always make an effort to maintain temperatures below 85 degrees (F), cannabis can handle higher temperatures and you’re probably not going to ruin your crop if your grow room peaks in the mid to upper 90’s during the day. Just make sure that you maintain excellent air circulation to prevent the heat from building up in hot spots and burning your plant more than necessary. Placing a fan in line with the top of your canopy and blowing toward your light can help prevent excess burning during peak temperatures. If you do notice serious burn occurring on the tops of your plant, you’re going to have to either add more ventilation to your grow room, an air conditioner,or just move your plants farther away from the light.

If low humidity is a problem, you can mist your plants during the cloning and vegetative growth stages, but you should refrain from misting during flowering as it can surely encourage fungal growth! There are also humidifiers available for purchase, or you can place a large dish of moist perlite in your grow space to help transpire more moisture into the air. When using perlite, it should not be swimming in water, and it would be advised to mix a dilute solution of hydrogen peroxide in with the water each time you moisten it, in order to help prevent mold growth. If this isn’t enough, you may need to fully dry the perlite on occasion, which can be accomplished by spreading it onto a foil lined baking dish and placing it in the oven for a while.

Low humidity (below 60% during vegetative growth or below 40% during flowering) can stress plants. However,some growers swear by lowering the humidity as much as possible during the last several days of flowering, as this may promote increased resin production by the plant as it attempts to prevent excess moisture loss by sealing itself off from the dry surrounding environment with the good THC-packed sticky stuff.

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So I’ve just checked tent & 64% humidity. That’s the best I can do with humidity ranging around 82% outside. This will be okay?

I’m having exactly the same issue. Important to keep the air moving around the tent. Not counting the exhaust fan, I have two clip on fans and a stand up fan in my tent moving the air. @Laurap

Having good air circulation will help reduce the chance of rot or mold. I can see in the shed right now it is 60 Degrees and 72% RH. Gonna go out now and check inside the tent.

63 and RH is 70% in the tent

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That’s what I’m dealing with! I put in the 260cflafter dehumidifier and charcoal couldn’t keep up. This morning o gladly saw 60s%

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Do you have good air movement in the tent? @Laurap

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Got two 6" blowing at the top and a 260 fan on bottom and of course exhaust. All on high. We never have Any rain from end of June till mid October but this year it’s rained at least every other day for 2 months and humidity is sending heat index into upper 110s.

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yep, it’s been crazy weather year for sure! Watch them closely for any signs of mold or bud rot and keep the air moving is about all you can do! I watered today and left my two BBA’s out in the sun so that they could get some rays and dry out!

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As Always, thanks so much.

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