High humidity - Am I necessarily doomed?

ScrubNinja · May 8, 2009

I'm doing a small cfl scrog in a Growlush propagation tent. I have a great 6 inch centrifugal fan extracting and a strong 120mm computer fan inside circulating the air. It's quite gusty in there, and rather overkill.

At day 12 of 12/12 my humidity ranges from about 70 to 85% which seems to be danger zone after doing a search here. I'm in the tropics and this is my first time flowering indoors.

By my reasoning, my plants outdoors did great in high humidity... even 100% humidity when it's raining and I've never had any serious mould problems... So will I be ok here considering I have so much ventillation? Surely conditions inside my tent are less condusive to mould than outdoors with it's rain, heavy dews, and generally high humidity?

I can't run a dehumidifier because I have a shared electricity bill with another place on the property, and I wouldn't be comfortable using any more power. I actually bought one today real cheap, it's 200 watts and that's more than my lights, lol.

Strains are Shiva skunk and The Pure. I've never grown them before but dude they came from doesn't mess around with mould susceptible strains so yeah, what does ICmag think? :1help:

IceColdCrickets · May 8, 2009

well first why is your humidity so high? where is your fresh intake air coming from?? you need to figure out why it is there and make sure you get fresh air inside the grow area. If you get fresh outside air in there it will reduce the chance for mold to multiple causing a problem for you.

ScrubNinja · May 8, 2009

I'm in the tropics, IceCold, plus it's a bit rainy. Right now it's a few hours into lights on, nearly 1am, and it's 83% ambient, and 71% inside the tent.

The air intakes at the bottom of the tent, about a metre off the ground (tent is on a cupboard) and it exhausts at the top of the room, into the same room but it's wierd, the wall is open at the top so some of the exhaust is leaving the room. I'll divert it so most of the flow exits the room, just that its a really open sort of house... theres no door back into the tent's room, and no top of the wall like I said. Thanks

dubbalicious · May 8, 2009

I feel your pain, grew in the islands and had the same issues. If your pulling air from the outside the humidity is gonna be real close to what the ambient is (outside). Dehum. was the only thing that worked for me, and it ran hard!! I'm sure your power is probably close to .30 a kwh, so thats def. more coins a month for sure. Dehum. was the only thing that worked for me, sorry I cant offer you more, good luck, be safe

Blunt_69 · May 8, 2009

Your gonna need to run a dehumidifier. The other thing that can help is raising your room temp.. Keep it under 28 degrees C though... This is even to hot, but it's a happy medium thing in this case

ScrubNinja · May 9, 2009

Thanks for the input fellas. I would run the demidifier if I could! Sucks that I have one just sitting there unused.

I guess I could simplify my question as "How come these plants are going to go mouldy when the same strains do great outside in higher humidity?".

Pharma Geddon · May 9, 2009

ScrubNinja said:
I guess I could simplify my question as "How come these plants are going to go mouldy when the same strains do great outside in higher humidity?".

I strongly suspect that it is using negative pressure that causes the mould problems, or rather lack of positive pressure.

I grew for years in my cellar with a makeshift '3 walls' effort, 4 uprights with panda plastic wrapped around to form the 3 walls. Gap at the floor the same as the height of the pots/buckets and at the top just enough height to bounce light from the reflector. A household tower fan a few feet from the open 'wall' and a 6" extractor fan and filter above, ducting to the outside.

The cellar is usually 80%+RH and I never had mould until I started growing in a tent down there and using negative pressure. Seems to be that the exhaust fan simply doesn't drag enough air in to do a proper job unless huge. Internal fans should take care of that in theory but I found it not to be so in practice.

For the tent I got a usb datalogger, cost a bit under £50 and well worth it imo. Let's you see exactly what's happening via a graph, minute by minute. The changeover time, lights off going to on was the main culprit, the dew point gets real close to the temps point, resulting in raindrops on the reflector. Half a year of jiggling fans around and playing with lights off heater timings got it sorted. During that time I switched to using Liquid Silicon as pH up so not sure what helped where, it's fixed now and I ain't messing with it, no mould for almost a year.

ScrubNinja · May 9, 2009

Cool, cool, interesting stuff. I have a few intake flaps that I could open up to reduce the pressure. I'll give it a shot! Thanks for input Pharma!

I've never used silica before, but I guess now would be a good time, huh? You've sold me on the datalogger, that sounds right up my alley.

ogatec · May 9, 2009

i live an a humid sweat box area too(ugg summer is here!)..i would try to do the most that you can to reduce humidity & find a strain that is mould resistant. most sativa based strains are a good starting point. I have also had great sucess with skunk based genetics. get the wrong genetics and bam! looks like a cotton factory in there! :fsu:

lots of air movment will help also.

forester · May 19, 2009

It might be worth trying one of those chemical dessicants in your grow tent. I think they are used to prevent smelly, muggy air from stinking up wardrobes/mould etc but they suck out moisture (apparenty 6-20 oz over a few weeks) you could be on a winner.

I'm not sure how effective it would be in various sized grow rooms/tent but may decrease the humidity by a fair bit if you are growing in a small tent.

eg.... http://www.builderssquare.com/Shop/results.aspx?kw=Damp Rid

ScrubNinja · May 19, 2009

Thanks all, I have been meaning to give those a shot, forester. So far Pharma's idea of minimizing the pressure seems to be working well - I think he might be onto something.

purpledomgoddes · May 19, 2009

high rh (low vapor pressure deficit) is not in itself a recipe for disaster. plants actually like higher rh.
your rh may be increasing due to their transpiration volume. if they are healthy, dont worry. damp-rid type rv/wardrobe dehumidifiers work ok w/out using a large machine unit.
main factor w/ high rh is the airflow. turbulent+laminate air flows keep condensation from forming (a problem), and keep the oxygen circulating. yes, plants use oxygen, as well as c02. earth's atmosphere is roughly 20% oxygen, so they need air movement too; even if in sealed environment.
this thread goes into detail about relative humidity/vapor pressure; may provide some relief+fundamentals of how plants react to wator vapor.
plants have broad range of comfort zone re rh. generally between 35-75% is manageable.

rh importance:
http://www.icmag.com/ic/showthread.php?t=112589&highlight=rh+importance

hope this helps. enjoy your garden!

ScrubNinja · May 20, 2009

Thank you purp, and I'd encourage anyone interested in any sort of humidity issues to read that link.

ScrubNinja · Jul 5, 2009

Followup:

I have pulled and dried the two Shiva Skunks and there was no mould at all, absolutely lovely smoke although it needs a cure of course. I pulled the Pure just a few hours ago and there's no mould on that either.

I only added a moisture eater thing which did barely anything/nothing, and focused on having the barest amount of negative pressure needed for the carbon filter to work. I never got around to getting silica. Humidity generally ranged from 60 to 80 percent RH through flower. Very very occasionally it hit high 50's and sometimes it was over 80.

I can only conclude that Pharma Geddon was spot on with those pressure observations. Thanks so much, man, and everyone for contributing.

exploziv · Jul 5, 2009

If you think there is still risk of mould, adding another fan for air movement should be cheap and doesn't use too much energy. :2cents:

Good luck! :wave:

CANNACO-OP · Jul 5, 2009

purpledomgoddes said:
high rh (low vapor pressure deficit) is not in itself a recipe for disaster. plants actually like higher rh.
your rh may be increasing due to their transpiration volume. if they are healthy, dont worry. damp-rid type rv/wardrobe dehumidifiers work ok w/out using a large machine unit.
main factor w/ high rh is the airflow. turbulent+laminate air flows keep condensation from forming (a problem), and keep the oxygen circulating. yes, plants use oxygen, as well as c02. earth's atmosphere is roughly 20% oxygen, so they need air movement too; even if in sealed environment.
this thread goes into detail about relative humidity/vapor pressure; may provide some relief+fundamentals of how plants react to wator vapor.
plants have broad range of comfort zone re rh. generally between 35-75% is manageable.

rh importance:
http://www.icmag.com/ic/showthread.php?t=112589&highlight=rh+importance

hope this helps. enjoy your garden!

Thanks for the link!

wondering if rather than a passive intake, one would add a same intake fan and use that for two fold, moving more air in, no negative pressure? and also help with more circulation then just the passive. In fact. I had one small op that the 3" intake was enough to provide fresh air and also move the canapy just wickedly! :2cents:

ScrubNinja · Jul 5, 2009

exploziv_gbb, thanks bro but I'm not sure if fans would help at this point

CANNACO-OP, you will need some negative pressure for the carbon filter to work effectively. Freezerboy discusses pressure in his Negative Pressure for Dummies thread. Peace.

exploziv · Jul 5, 2009

Now a pipe or some smoking papers should do the trick.. :laughing:

Buds looking good! Did you had mould problems or something?

ScrubNinja · Jul 5, 2009

Haha thanks. Well, I had humidity problems but managed to avoid mould with some helpful suggestions. I had a thread about it, it was very interesting. Take care

buddin_904 · Jul 6, 2009

someone with knowledge, whats the correlation between RH and trich concentration

High humidity - Am I necessarily doomed?

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