Optimal Relative Humidity, and How to Control?

Dogwap · Oct 28, 2011

Three simple questions...

What is the optimal RH for growing weed?

Does this range change with the stage of growth?

Just added three clones to a 30"X20"X72" cabinet and the RH is 33%. If this is too low, what are my options for increasing it?

Thanks

ttystikk · Oct 29, 2011

Dogwap said:
Three simple questions...

What is the optimal RH for growing weed?

Does this range change with the stage of growth?

Just added three clones to a 30"X20"X72" cabinet and the RH is 33%. If this is too low, what are my options for increasing it?

Thanks

1. the optimal relative humidity for growing most plants, this included, changes based on temperature. In general, you want humidity to go up with rising temps. Look up and study VPD, or Vapor Pressure Differential, for more details. A good starting point would be around 70% relative humidity at 80 degrees fahrenheit.

2. Veg and early bloom like plenty of humidity. You can decrease it somewhat in that last week or two of flower, but I wouldn't overdo it.

3. Swamp cooler, hang wet towels and blow air through/across them... Reduce your air turnover.

Good luck!

symbiote420 · Oct 29, 2011

Yeah tty my plants like the humidity around 70% in seedling and veg. stage, in the later weeks like wk5 of bloom to harvest I keep it around 40% - 50% RH, I found that some strains really pack on the trichs when the humidity is even lower like 30% or so in the final weeks. Hope that helps!!!

Bunz · Oct 29, 2011

I shoot for 70% during veg and 40% during flower.

Increase..........tray of water with a fan blowing across it

Decrease.......buy a dehuey............one of the best investments I've made

Bunz :D

ogplatinum · Oct 29, 2011

Bunz said:
I shoot for 70% during veg and 40% during flower.

Increase..........tray of water with a fan blowing across it

Decrease.......buy a dehuey............one of the best investments I've made

Bunz :D

But how do I run my (?) 7amp 20pint dehuey that I found in my garage that came with my house along with 3 others....one my skimpy ass 12amp breaker for my op.....hmmm..

I wish!!! FUCKKK

green guy · Oct 29, 2011

ttystikk said:
1. the optimal relative humidity for growing most plants, this included, changes based on temperature. In general, you want humidity to go up with rising temps. Look up and study VPD, or Vapor Pressure Differential, for more details. A good starting point would be around 70% relative humidity at 80 degrees fahrenheit.

2. Veg and early bloom like plenty of humidity. You can decrease it somewhat in that last week or two of flower, but I wouldn't overdo it.

3. Swamp cooler, hang wet towels and blow air through/across them... Reduce your air turnover.

Good luck!

Lately I've been managing plants by VPD and the plants in the veg room love it. I use fine misting to increase RH as required and just open the door for a brief period to lower it.

Here's a great tool someone else on the site provided:

http://www.autogrow.com/vpd_calc.php

MTgrower · Oct 29, 2011

green guy said:
Lately I've been managing plants by VPD and the plants in the veg room love it. I use fine misting to increase RH as required and just open the door for a brief period to lower it.

Here's a great tool someone else on the site provided:

http://www.autogrow.com/vpd_calc.php

Here is some more info on VPD from Maximum Yield:

Bunz · Oct 29, 2011

ogplatinum said:
But how do I run my (?) 7amp 20pint dehuey that I found in my garage that came with my house along with 3 others....one my skimpy ass 12amp breaker for my op.....hmmm..

I wish!!! FUCKKK

Your 20 amp dehuey uses 7 amps? OUCH!! My 45 pint until is only tagged at 2.9 amps.

Gotta read up on the VPD thing. I love Maximum Yield..........learned a LOT there!!

Bunz :D

ogplatinum · Oct 29, 2011

Bunz said:
Your 20 amp dehuey uses 7 amps? OUCH!! My 45 pint until is only tagged at 2.9 amps.

Gotta read up on the VPD thing. I love Maximum Yield..........learned a LOT there!!

Bunz :D

I cant really understand what its really pulling. It says like 12amps max power on the fucker. And There is so many amp readings on the back. My landlord gave me 2, 20 pinters with our rental agreement. How they're used? Well...:banana1sv6::banana1sv6::banana1sv6::banana1sv6:

Dogwap · Oct 31, 2011

Thanks guys. I like the wet rag idea, since I'm growing in a cabinet.

My 6-9" clones were transplanted 6 days ago.

My RH has been in the mid to low 30s.

What are the symptoms of low RH?

Again, thanks for the help.

ttystikk · Nov 2, 2011

Dogwap said:
Thanks guys. I like the wet rag idea, since I'm growing in a cabinet.

My 6-9" clones were transplanted 6 days ago.

My RH has been in the mid to low 30s.

What are the symptoms of low RH?

Again, thanks for the help.

The main symptom of low RH is that the stomata on the undersides of the plants' leaves stay closed, in order to prevent the plant from drying out too fast. Since this is also where they breathe in CO2 and breathe out O2, what's going on is your girls are growing more slowly than they would with better humidity conditions. Another issue could be nutrient burn if you are running a strong dose of nutes- since the plants have to pull a lot of water to keep from drying out too much, they'll also take up a lot of nutrient, and if there is a high concentration of nutrients it can lead to burning. This doesn't mean you actually have to have excessively high nutrient concentrations, because what might burn plants at low RH values may well be ideal for them in higher RH conditions.

Also, one of the precepts of VPD theory is that RH needs to rise as temperature rises. 50% RH is fine at 60 degrees F, where you want 60% at 70 degrees F, and at least 70% RH at 80 degrees F. You'll want to raise your RH value to better match the temperature of your cabinet, whatever you like to keep it at.

Dogwap · Nov 2, 2011

Extremely interesting and enlightening. Thanks for the detailed explanation and link to the Maxyield article.

I understand the relationship much better now, and the importance of keeping RH (more importantly VPD) in the correct range.

My plants have barely grown in the week that I've had them. But the roots are taking off like crazy. Now I understand why.

Thanks a ton!!!

ttystikk · Nov 2, 2011

Dogwap said:
Thanks guys. I like the wet rag idea, since I'm growing in a cabinet.

My 6-9" clones were transplanted 6 days ago.

My RH has been in the mid to low 30s.

What are the symptoms of low RH?

Again, thanks for the help.

Symptoms of excessively dry conditions include lots of water use, potential nutrient burn, and slow growth since the plants are working too hard at staying hydrated to grow at their best rate.

You can use the wet rag to help maintain a higher RH, but to get the humidity up right away, the misting idea is a very good one. Feel free to mist with foliar sprays that provide nutrients, no reason you can't do two things at once.

theTinker · Nov 2, 2011

Is there a list of RH optimal ranges for different temperature levels?

I'd like to start running CO2 at roughly 90F, would 70-80% humidity be a aim?

Dogwap · Nov 3, 2011

Stick,

Thanks for the tips. Last night I hung a washcloth above a small container of water so that it will wick as the the water evaporates. I doubt that this method will get me the 40% gain I need, but it's a start.

Tink,

The Maximum Yield artical the VPD calculator linked on the first page of this thread will give you the optimal RH for the temp you want to run.

Dogwap · Nov 3, 2011

Has anyone used a cigar humidifier? They generally are set to maintain about 75% RH and are small enough to fit in a medium sized cabinet. I don't know if they are powerfull enough though.

Buddy Hemphill · Nov 7, 2011

I tried all the wet stuff hanging up tricks.

If you want consistency buy a real humidifier and a good controller.

Heres the thing with band aid RH cures. If its 40% RH outside and it takes 2 towels and a wet t shirt......what happens if its 30% RH? 3 wet towels, 2 wet t shirts and a box fan blowing into a pan of water?

To "iffy" for me. I bought a good humidifier and it was money WELL spent.

Without environment AND genetics.....mediocre is the best anybody can acheive, IMHO. The room HAS to be right for repeatable results.

true grit · Nov 7, 2011

Ok first learn your VPD ranges you are shooting for. Once you get a range, buy yourself a Humidity controller of some sort- for a cheapie scoop a HUM-1. It has a probe that measures and operates both a humidifier and dehumidifier. Now the important part- DO NOT CHEAP OUT on a huey/dehuey.

When the ideal VPD is there, the room varies little and humidity control doesn't move around as much. Ideally, your temperature is controlled and you have very little swing in temp between light to dark cycles, as well as little humidity shift. the bigger the swing the more health issues I've found.

MrStonerMan · Nov 7, 2011

So what is the VPD one should aim for with Marijuana?

green guy · Nov 9, 2011

According to their website, its .85.

From experience, plants flourish at this level in the veg stage. I don't have enough experience flowering them to know if that is the case in bloom as a lot of what you reads contradicts a RH level high enough to achieve .85 in bloom, but in veg they will love it.

Optimal Relative Humidity, and How to Control?

Optimal Relative Humidity, and How to Control?

Dogwap

ttystikk

symbiote420

Bunz

ogplatinum

green guy

MTgrower

Bunz

ogplatinum

Dogwap

ttystikk

Dogwap

ttystikk

theTinker

Dogwap

Dogwap

Buddy Hemphill

Guest

true grit

MrStonerMan

green guy

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