Lowest Acceptable Relative Humidity 4 Indoor Hydroponics? +rep 4 citing your sources

Dipsomaniac420

Dipsomaniac420

Well-Known Member
So I read lots about growing ganja...a hand full of books, magazines, and endless online content. What I hardly ever hear about is a rare problem of too low of a humidity.

I live in a place where the Relative Humidity (RH) is about 20% naturally year around and so is my indoor grow area. So, my question for ya'll...

What is the lowest RH level for indoor hydro that will allow plants to flourish?

My assumption is that RH isn't a problem because plants can't really dry out in hydroponics unless the roots aren't able to uptake the water for one of many reasons.

I do understand how easy it is to bring RH levels up, in comparison to down. That is something I would like to avoid however.
 
Dipsomaniac420

Dipsomaniac420

Well-Known Member
From THIS site: At a lower RH, the stoma keep releasing water until the plant dries out. At that moment, the stomata close. Then, the intake of CO2 stagnates, and plant growth is impaired.
 
baconpopcorn

baconpopcorn

Member
Funny you bring up this thread/question. So my current grow started out at 0% RH and I had issues with nute burn but everything else seemed fine. Then I read pretty much the same thing you did, about how the stomata keeps releasing water etc..

The thing I found most interesting is even though my PPM's were low compared to what the feeding charts said even at 1/2 strength I was seeing burn. So I lowered it 1/4 from the feeding chart and saw an explosive growth. I'm going to go out on a limb here and say since the stomata was pretty much open dumping water that the roots were sucking up nutrients at a MUCH faster rate than the plant needed, hence the burn.

I also noticed once I added a humidifier and set it around 50% I could raise the PPM's higher with ease. For vegging I read you should be around 60~70% and for flowering around 40%.
 
Dipsomaniac420

Dipsomaniac420

Well-Known Member
baconpopcorn said:
Funny you bring up this thread/question. So my current grow started out at 0% RH and I had issues with nute burn but everything else seemed fine. Then I read pretty much the same thing you did, about how the stomata keeps releasing water etc..

The thing I found most interesting is even though my PPM's were low compared to what the feeding charts said even at 1/2 strength I was seeing burn. So I lowered it 1/4 from the feeding chart and saw an explosive growth. I'm going to go out on a limb here and say since the stomata was pretty much open dumping water that the roots were sucking up nutrients at a MUCH faster rate than the plant needed, hence the burn.

I also noticed once I added a humidifier and set it around 50% I could raise the PPM's higher with ease. For vegging I read you should be around 60~70% and for flowering around 40%.
Click to expand...

Good information...thanks

Questions though...

1. if your plant(s) was absorbing so much water and releasing it, did you notice that your reservoir was losing water quickly?

2. instead of lowering the amount of nutrients, why not dilute it (assuming the system can handle more H20)? If plants are transpiring water that quickly, a large reservoir should allow them to do that and slow the amount of nutrients they would uptake because it would be a more dilute solution.

3. In my link, it said the stoma keep releasing water until the plant dries out... how could a hydroponically grown plant dry out? and thus how could a minimum relative humidity affect indoor hydroponics unless you let your plant "dry out"?
 
Dipsomaniac420

Dipsomaniac420

Well-Known Member
I just really do not want to add humdity to my room. Mainly because my veg room is too closely tied to my flower room in terms of air quality...so raising the humidity in one room wouldn't do me any favors in my flowering room, especially considering the powdery mildew I've been having. Thus I'm wondering why relative humidity, especially in veg, really matters in hydroponics. I don't understand how the stoma can dry out unless the plant dries out....CAN ANYONE HELP?

Bueler?

Bueler?





Bueler?
 
Encomium

Encomium

Active Member
From what I understand and according to Cervantes' in his Indoor/Outdoor bible the ideal RH for vegetating is 80% and half of that for flowering (40%). When I had my plants vegging they were sitting at around 25-35% even after adding a small humidifier. Most people on these forums from what I've read don't really stress out that much over RH around 25%. Personally I think it's more of a min/maxing type of control where ideally the RH would be nearer to 80% for rapid growth in the vegetative state yet not having an extreme impact if say the RH was 20% (like yours).

Also keep in mind that RH is an indicator of how much water air can hold at a given time so your average temperature is going to matter quite a bit on how your plants transpire (breath) and intake water.
 
Dipsomaniac420

Dipsomaniac420

Well-Known Member
Encomium said:
From what I understand and according to Cervantes' in his Indoor/Outdoor bible the ideal RH for vegetating is 80% and half of that for flowering (40%). When I had my plants vegging they were sitting at around 25-35% even after adding a small humidifier. Most people on these forums from what I've read don't really stress out that much over RH around 25%. Personally I think it's more of a min/maxing type of control where ideally the RH would be nearer to 80% for rapid growth in the vegetative state yet not having an extreme impact if say the RH was 20% (like yours).

Also keep in mind that RH is an indicator of how much water air can hold at a given time so your average temperature is going to matter quite a bit on how your plants transpire (breath) and intake water.
Click to expand...
+rep, thanks for the info.

I've got Cervantes' Bible...about to read it for a second time actually. A lot of the information in the book though doesn't mention if there's a difference for hydro vs soil in its recommendations. If you find one pertaining to RH, can you point me to a page number?

My question is why does the RH matter if its too low for hydroponics?

I might have to start another thread "Why is there a mimimum RH for hydroponics?"

My avg temp is about 72-75F in my veg room.
 
thexception

thexception

Well-Known Member
It seems even in hydro, the low humidity can reduce the carbon dioxide intake by the plant which in turn, will reduce photosynthesis & account for slower plant growth. Granted I am not a hydro person so I might not know what the hell I am talking about :)
 
thexception

thexception

Well-Known Member
btw i have the cannabis grow bible too, which says 40-80%, also nothing I have found much more specific then that or related to hyrdo, I think I have picked up more specific knowledge about this subject in general on the internet over time.
 
Dipsomaniac420

Dipsomaniac420

Well-Known Member
thexception said:
It seems even in hydro, the low humidity can reduce the carbon dioxide intake by the plant which in turn, will reduce photosynthesis & account for slower plant growth. Granted I am not a hydro person so I might not know what the hell I am talking about :)
Click to expand...
Hey, I'll take that answer at least into consideration...that's miles ahead of what I've heard so far. Soil or Hydro....it would make sense that it doesn't matter. My next question for that answer would be how or why does low RH reduce the ability of a plant to uptake CO2?

I just found this:
"The relative humidity affects the rate of the plant's transpiration. With high humidity, water evaporates from the leaves more slowly; transpiration slows, and growth slows also. With low humidity, water evaporates rapidly; the plant may not be able to absorb water fast enough to maintain an equilibrium and will protect itself from dehydration by closing its stomata. This slows the transpiration rate and growth also slows. There is a noticeable slowing of growth because of humidity only when the humidity stays at an extreme (less then 20 percent or over 90 percent)." from HERE

So it would seem that there theoretically might not be a minimum low RH, the prerequisite would be that your plant has to be able to uptake the water....if for any reason that doesn't happen, then the low RH will only compound the problems you'd be experiencing from the plants inability to uptake the water as fast as it needs to.

Waduhya think?
 
C

CHUCKTYLAH

Active Member
Your plant releases water faster than the roots can draw water when the humidity is too low thats why even in hydroponics your plant will dry out. Your plants dont take in more water because there is more water there or hydroponics wouldn't work.
 
Dipsomaniac420

Dipsomaniac420

Well-Known Member
CHUCKTYLAH said:
Your plant releases water faster than the roots can draw water when the humidity is too low thats why even in hydroponics your plant will dry out. Your plants dont take in more water because there is more water there or hydroponics wouldn't work.
Click to expand...
That's a great theory, I want to believe it....got any references?
 
thexception

thexception

Well-Known Member
With low humidity, water evaporates rapidly; the plant may not be able to absorb water fast enough...

there is ur answer right there, so whether or not the water is available is not the issue, like Chuck said. The humidity relates to the entire plant system, not just the roots. Humidity effects the stems, stomata, leaves, etc. which whether in soil or hydro, it doesn't change the fact the low air humidity is there & is affecting the entire plant system. It will also cause yellowing & diminished yield just like in soil.

That being said, I think collectively we have ascertained that u need to get a humidifier. :)

http://www.google.com/url?sa=t&source=web&cd=1&sqi=2&ved=0CBgQFjAA&url=http%3A%2F%2Fwww.thefreedictionary.com%2Fascertained&ei=dnmCTd7lLYKmvgOl3OXFCA&usg=AFQjCNFhZnGzAR4DnZ_2bvSgmLGC2EG_KQ
 
Dipsomaniac420

Dipsomaniac420

Well-Known Member
thexception said:
With low humidity, water evaporates rapidly; the plant may not be able to absorb water fast enough...

there is ur answer right there, so whether or not the water is available is not the issue, like Chuck said. The humidity relates to the entire plant system, not just the roots. Humidity effects the stems, stomata, leaves, etc. which whether in soil or hydro, it doesn't change the fact the low air humidity is there & is affecting the entire plant system. It will also cause yellowing & diminished yield just like in soil.

That being said, I think collectively we have ascertained that u need to get a humidifier. :)

http://www.google.com/url?sa=t&source=web&cd=1&sqi=2&ved=0CBgQFjAA&url=http%3A%2F%2Fwww.thefreedictionary.com%2Fascertained&ei=dnmCTd7lLYKmvgOl3OXFCA&usg=AFQjCNFhZnGzAR4DnZ_2bvSgmLGC2EG_KQ
Click to expand...

<::sigh::> yeah i think that's gotta be it....ok cheers, well done ya'll thank you kindly =)

At least humidifiers are cheap. Shoot...I might even just make my own.
 
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