# humidity



## babymonkey (Feb 21, 2010)

hi guys
ive switched to 12/12 for flowering just 2 days ago,i switch on at 10am & switch off at 10pm,when the light & fans etc. are switched on the humidity is around 50 which is good i think,but in between 10pm - 10am while the lights are off,my humidity goes upto 80%...

my question is ...with the humidity going aqll the way upto 80,is this going to be damaging to the plants?,also if it does what can i do to bring the hunidity down to around 50%

thanks all


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## BBFan (Feb 21, 2010)

Hello babymonkey-

Even 50% humidity is a little on the high side.  Flowering mj thrives in an arid climate.  Also, too much humidity can lead to bud rot.

Have you tried running your fans 24/0?  That might help with the humidity, and good air exchange is always beneficial.

How low do the temps get during lights off, and how high do they get with lights on?

A dehumidifier, while costing a few hundred bucks, may be a good investment.  My experience though is that they tend to increase temperatures.

Good luck to you!


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## babymonkey (Feb 21, 2010)

BBFan said:
			
		

> Hello babymonkey-
> 
> Even 50% humidity is a little on the high side. Flowering mj thrives in an arid climate. Also, too much humidity can lead to bud rot.
> 
> ...


 
hi BBFAN,thanks for reply

i havnt tried running my fans 24/7,but i might give it ago as you got me worried about bud rot.

temps with the lights on ,is about 76 - 80 degrees.
temps with lights off,i know goes down to 58 degrees

i have tried a dehumidifier,as you said it does raise the temp up,also it seem to raise my PH in the feed by 0.5 a day,this was the main reason i took it out of the tent

when you say about keeping the fans running,i have an 8 inch extractor taken air out of the tent,a 6 inch extractor bringing air into the tent,also an osculating fan blowing over the top of the plants.

do i have to keep all of them running or just the osculating fan ?

thanks


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## BBFan (Feb 21, 2010)

Babymonkey-

Can you run the dehumidifier during lights off?  Your daytime temperature is near perfect, but 58 degrees F is just a little on the cold side.

How was it affecting your ph though:confused2:   I've never heard of that, or did I misunderstand?

As far as the fans, can you check the rh outside your tent?  If it's lower, just use the intake and exhaust fans and that should take care of the humidity.  If the outside rh is higher, try just the oscillating fan.

Good luck!


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## nouvellechef (Feb 21, 2010)

I run fans 24/7 and De-humidifier is set it and forget it at 40% on top of a rez.


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## docfishwrinkle (Feb 21, 2010)

babymonkey said:
			
		

> temps with the lights on ,is about 76 - 80 degrees.
> temps with lights off,i know goes down to 58 degrees
> 
> i have tried a dehumidifier,as you said it does raise the temp up,also it seem to raise my PH in the feed by 0.5 a day,this was the main reason i took it out of the tent
> ...


 
hey BM sounds like you might need a space heater for that tent. 58* is a lil chilly. shoot for mid 60's. 

how did you come to find out a dehumidifier raised your ph? never heard this before just curious. you are maybe doing hydro?

yes IMO leave all fans running.


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## dman1234 (Feb 21, 2010)

Just a thought but are you getting an accurate humidity reading
80% seems very vey high.


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## babymonkey (Feb 21, 2010)

docfishwrinkle said:
			
		

> hey BM sounds like you might need a space heater for that tent. 58* is a lil chilly. shoot for mid 60's.
> 
> how did you come to find out a dehumidifier raised your ph? never heard this before just curious. you are maybe doing hydro?
> 
> yes IMO leave all fans running.


 
thanks m8,ye when i was using my dehimidifier my ph kept rising,now ive taken it out my ph is stable,i didnt really change anything else so im just assuming it was the dehumidifier that was rising the ph as im doing hydro

the only problem i have with running all fans of a night is the tent is in my bedroom & the fans make too much noise

hopefully after another solution


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## babymonkey (Feb 21, 2010)

BBFan said:
			
		

> Babymonkey-
> 
> Can you run the dehumidifier during lights off? Your daytime temperature is near perfect, but 58 degrees F is just a little on the cold side.
> 
> ...


 
hi bbfan
i only have 1 thermometer to check humidity which is inside my tent,but im going to buy another 1 in next 2 days,by what you mentioned above i hope the humidity is higher outside the tent so i can just leave my osculating fan on,instead of all fans

thanks m8


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## babymonkey (Feb 21, 2010)

:d


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## Rosebud (Feb 22, 2010)

My humidity is 33 and temp is 73. I am in great flowering now and wondered it I should up the humidity? Help.


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## Funkfarmer (Feb 22, 2010)

Do whatever you can to get the humidity down, I had high humidity with lights off and it led to powdery mildew and it was hard to get rid of.


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## babymonkey (Feb 22, 2010)

just a couple of questions on whats the best temp & humidity figures

1)in veggie stage with lights on whats the best temp for temperature &    himidity ?

2)in veggie stage with lights off whats the best temp for temperature & humidity ?

3)in flowering stage with light on,best temps for temperature & humidity ?

4)in flowering stage with lights off,best temp for temperature & humidity ?

hopefully people can give there own opinions & answers on the above 4
questions & maybe make it all clear for everyone else to read as i always see people asking for these figures about humidity & temp all over the forumn

thanks all


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## BlueNose (Feb 22, 2010)

1,2)75 deg. F , 60-70% 
3,4) 75 deg. F , <40%
(temp. high<day> 80F), (low<night> 70F) is my goal no matter what stage of growth with 75 F being optimum.

I use a small heater at night to keep heat up


*Solely my opinion*- I like higher humidity during veg. My thought is that the plants grow a bit better when the leaf and trunk/branch surfaces are able to interact with moist air rather than taking all the required moisture from the soil. This is completely my opinion and very unproven so take it with a grain of salt....I haven't had anything negative happen though.


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## Rosebud (Feb 22, 2010)

According to Marijuana Horticulture by Jorge Cervantes:

         "The best relative humidity range:
                                               Vegetative: 60-70%
                                               Flowering 40-60%
                                               clones     80-95%"




The moisture holding capacity of air doubles with every  20 degrees F (10 degrees C) increase in temperature.




I haven't read about lights being on or off matters. The temperature does matter with regard to humidity. I hope this helps. After reading this I misted to bring mine up to bring it back to 40%. This is the only book I have, I don't know if everyone agrees with him or not..We will see.


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## babymonkey (Feb 22, 2010)

Gonna Eat That? said:
			
		

> 1,2)75 deg. F , 60-70%
> 3,4) 75 deg. F , <40%
> (temp. high<day> 80F), (low<night> 70F) is my goal no matter what stage of growth with 75 F being optimum.
> 
> ...


 
hi m8
thanks for the info,what type of small heater do you use at night to keep the temps up ?

cheers m8


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## BlueNose (Feb 22, 2010)

just a cheap two setting 900/1500 watt with a digital temp setting. You can get them at Target, Home Depot etc. 

I have pretty good airflow so I set mine at 77F and it keeps my temps about 70-72 on cold nights(roughly 30-40F)


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## babymonkey (Feb 22, 2010)

Gonna Eat That? said:
			
		

> just a cheap two setting 900/1500 watt with a digital temp setting. You can get them at Target, Home Depot etc.
> 
> I have pretty good airflow so I set mine at 77F and it keeps my temps about 70-72 on cold nights(roughly 30-40F)


 
thanks m8
definatly going to be investing in 1 of those

thanks


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## BBFan (Feb 22, 2010)

babymonkey said:
			
		

> 1)in veggie stage with lights on whats the best temp for temperature & himidity ?
> *78 deg F / RH 50% - 70%*
> 
> 2)in veggie stage with lights off whats the best temp for temperature & humidity ?
> ...


 
Just my thoughts. MJ prefers humidity during veg and aridity during flower.

MJ does not require a dark period during vegetative growth.  Light independent reactions occur during lights on or lights off.

Ideal temp for photosynthesis for many leafy C-3 plants (like mj) is around 78 deg F without supplemental or enriched co2.


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## PUFF MONKEY (Feb 22, 2010)

58f at "night" is the reason for the humidity jump..try a cheap space heater set to 65f and run your ventilation 24/7.


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## dman1234 (Feb 22, 2010)

my home has a very low humidity, 20-27%

its ideal for flower and it has never had an affect on my veg room, 
im in soil so i dont know if that makes a difference?

the worst part of low humidity is dry my bud, it dries to fast, i have to 
use a swamp cooler in my drying room.

Maybe i should get my furnaces humidifier fixed        :hubba:


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## legalize_freedom (Feb 23, 2010)

yeah I was going to say the same thing as Puff...IMO its the extreme change in temp, also as the plant grows it takes up more volume than a smaller one, decreasing air space.


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## babymonkey (Feb 24, 2010)

hi all
can someone please have a look at the link below,its only a small blow heater,just wondering if i could put this in the tent of a night & it would keep the temps up & the humidity down without the lights on.

 

hxxp://www.argos.co.uk/static/Product/partNumber/4151371/Trail/searchtext%3EBLOW+HEATER.htm


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## legalize_freedom (Feb 24, 2010)

I'd be careful with putting it directly in the tent, if it is forcing hot air onto the plants it could cause them to wilt and die.  I'm sure you know heat rises so the overall temp of the tent may be reading cooler, then what is coming directly from the heater, so if this is close to the plants it could cause problems.  If it were me I would place the heater outside of the tent, close to the fresh air intake, and let the warmer air be pulled in along with fresh air, rather than haveing the heater sitting in the space with the plants.


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## babymonkey (Feb 24, 2010)

legalize_freedom said:
			
		

> I'd be careful with putting it directly in the tent, if it is forcing hot air onto the plants it could cause them to wilt and die. I'm sure you know heat rises so the overall temp of the tent may be reading cooler, then what is coming directly from the heater, so if this is close to the plants it could cause problems. If it were me I would place the heater outside of the tent, close to the fresh air intake, and let the warmer air be pulled in along with fresh air, rather than haveing the heater sitting in the space with the plants.


 
hi legalize_freedom
i think you hit the nail on the head,thats a cracking idea as i would of put it in the tent,and didnt know it`ll cause harm to the plants,i love the help off this site,with all the ideas & solutions

happy smoking


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## Althea (Mar 14, 2010)

nouvellechef said:
			
		

> I run fans 24/7 and De-humidifier is set it and forget it at 40% on top of a rez.


 
Me too - with CO2 as well.  Regarding this original post - I think something else must have been causing the ph creep, a dehumidifier would only be capable of altering ph if you removed so much (over 50% more like 75%) of your reservior water without replacing it that you concentrated your nutes and locked out.  They dont otherwise have the ability to alter ph in water, all they do is suck water out of the air.

Yes, just like an air conditioner, a dehumidifier is really a type of heat sink and causes heat as a byproduct of it functioning.  A surprising ammount of it.  I am working on mine regarding this.  It blows all the heat out of a slotted area in the back via a heavy duty fan, I am trying to seal off the back, make basically a big funnel that narrows down to my vent duct size then I want to tap that exhaust into the outgoing duct and hopefully at least half the heat will end up outside not blowing around my growroom.

58F at night is too low if your days are that high - its dang low anyways but you have like a 30 degree F difference in your light and dark cycle. When the warm air cools the moisture in it (humidity) has to go somewhere.  Its an elemental law of enviornmental physics.  So it condenses.  Usually in your buds.  Resulting in molds, mildews, and *baaaaaad* budrot.  During flowering Ed Rosenthal reccomends humidity "...at 50% - 55% and your mold problems will cease." (Ask Ed best of).  You are too humid and are asking for budrot and molds.  Fans help a lot, I run my vent fan with my CO2 so its complicated but before I had CO2 I ran the vent fan (a 10" vortex in 12" out) at a rate that could remove the air in the room in just about a minute.  Thats overkill but budrot sucks.

Environmental fans (blowing on the plants) I leave on 24/7 for same reason plus bugs hate it.

I think your solution is to have the dehumidifier run at night and off during light period.  This excess "waste" heat will keep the temp and humidity stable and higher - probably exactly what you need.  Not waste at all - you get a two-for-one.  One is the benefit of the right humidity range so you dont get rot.  Two is the temp stability which results from the dehumidifier running so what most people view as a negative side effect (the heat) you actually benefit from - plus dont forget cannabis doesnt like the temperature to swing that large a range.  You will see better growth and larger more compact flowers if you narrow the range down to 15 degrees (from the night low to the light high).  

If "the purple" is all the rage for you a temp drop at the last few days of flowering to 55F (you are close) will cause a lot of strains to turn a purplish color to intense almost neon purple.  Just a trick I use for friendly purple-heads who refuse the exact same strain as inferior and harsh and weak will jump up and down and rave about the SAME PLANT even if I harvested part while it was green then let it get its 55F purple color change.  If anything it actually causes a reduction in THC from degredation to the thc glands becoming brittle and breaking the tops off leaving just the little stem part and losing the mushroom shaped blob at the tip.  Just goes to show the power of the placebo effect as far as Im concerned, and the silly behavior you get when Snoop Dogg sings about weed being a purple color - all the sudden nothing but purple is "hip"

I hope this helps, contact me if you wish for any further help or for source data.

Al


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