Optimal Relative Humidity, and How to Control?

[Dogwap]

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.

Dude,

You're preaching to the choir. Take a look at the opening post. I'm growing in a small cabinet.

Do you know of a humidifier that works in a cabinet that is 30" X 20" X 49" tall? The only ones I could find are for cigars.

Regarding VPD... The artical and calculator referenced above make figuring this out very simple. In my case, and most people's, 70-75% RH will put you right where you need to be.

 

[Buddy Hemphill]

Dude,

You're preaching to the choir. Take a look at the opening post. I'm growing in a small cabinet.

Do you know of a humidifier that works in a cabinet that is 30" X 20" X 49" tall? The only ones I could find are for cigars.

Regarding VPD... The artical and calculator referenced above make figuring this out very simple. In my case, and most people's, 70-75% RH will put you right where you need to be.

http://www.hydrofogger.com/

I have the big one in a 20x20 space. They make a small one I cant speak for. The big one lets me control RH how I want to.

All props to Jalisco Kid for the info. I was doing the wet shit everywhere thing, also. He uses a Faran, which I couldn't find.

They are pricey...but at that point, for me, it was throw in the towel or step up to the pump.

There is a huge difference in veg between 30-40%rh and 65-75% rh. The plants just wake up. I have a CAP controller running the unit.

 

[Buddy Hemphill]

Theres also the ones for kids at Wal mart. I couldnt tell it was on, but in a closet...maybe?

 

[Buddy Hemphill]

FWIW...JK is who put me onto 70% RH also. The dude knows his shit.

I have never heard of VPD before. I need to research this a little.

 

[Dogwap]

Buddy,

Those Humidifiers look really nice. But even the mini version has a 12" by 12" foot print and is meant to humidify 150 to 1,000 cubic feet. My cabinet has only about 16.

How about a humidor humidifier? They're small, and affordable. But are they powerfull enough?
Several can be found at this site.

 

[green guy]

http://http://hydrofogger.com/

I have the big one in a 20x20 space. They make a small one I cant speak for. The big one lets me control RH how I want to.

All props to Jalisco Kid for the info. I was doing the wet shit everywhere thing, also. He uses a Faran, which I couldn't find.

They are pricey...but at that point, for me, it was throw in the towel or step up to the pump.

There is a huge difference in veg between 30-40%rh and 65-75% rh. The plants just wake up. I have a CAP controller running the unit.

The Hydrofogger looks interesting and the minifogger seems reasonably priced to do a room up to 1000 sq feet.

Does anyone know what the optimal RH for flower is? I agree with you that in veg the plants do wake up at those levels. I follow the VPD guidelines but are they the same for flower? That would give RH levels that seem higher than common accepted practices for the bud phase.

 

[lightit]

yeah those vpd guidelines seem a little high especially for late flower. for instance, if i was running a room with co2 at 87 degrees and was shooting for 0.85 kpa, my optimal rh would be above 80%. i have always been told that especially with denser buds, mold can become an issue at above 60% rh, not to mention transpiration might be an issue with such high temps and high humidity. most of the conventional mj books i have say something like this: clones 80-95%, veg 60-75%, flower 40-60%. i guess i need to do some more reading on vpd, maybe i am not understanding it correctly. on an interesting side note, i have been told that when humidity is too low during late flower, the trichome heads lose the elasticity required to swell to their full potential, so trying to guard against mold by dropping the rh too low could have some negative effects.

 

[Dogwap]

Lightit,

Good points. I don't I think the VPD numbers take mold into account. My understanding is that they are solely used to predict the optimal conditions for nutrient uptake.

In any case, I've gone ahead and ordered a fogger from sunflower supply that is typically used for fog-ponic systems. Haven't fully though out how I'll incorporate it, but it only costs $31 so I won't be too far in the hole if it doesn't work.

 

[green guy]

Lightit,

Good points. I don't I think the VPD numbers take mold into account. My understanding is that they are solely used to predict the optimal conditions for nutrient uptake.

In any case, I've gone ahead and ordered a fogger from sunflower supply that is typically used for fog-ponic systems. Haven't fully though out how I'll incorporate it, but it only costs $31 so I won't be too far in the hole if it doesn't work.

Thanks for the link, I've been looking for a fogger to play with and ordered one myself. Looks like a good site, though being in Canada I don't want to order grow lights or something obvious and give customs my address.

 

[MrStonerMan]

how did the fogger work for you guys? Any pics of how you incorporated it?

 

[green guy]

how did the fogger work for you guys? Any pics of how you incorporated it?

No pics but should be easy to describe.

I have the 3 head fogger set up in a 4 x 4 tent. I have the fogger in 1 18 ga Rubber maid tote. I installed the PC fan in the top of the lid of the tote. Then I cut a 3 1/8" hole with a holesaw to fit a 2" bulk head and hard piped a 9" PVC pipe to a Tee to 2 other 18 ga Rubbermaid totes. The plants are in these two totes. I also have about 4 inches of nutrient solution in the bottom of the totes. I was told that to attempt to do it without DWC is asking for trouble. I have air stones and my home made bubblers in all 3 totes.

The fogger is actually self defeating with out a timer. Things get way too wet if it runs full time. I had to incorporate a timer and run it on for a minute, off for 15 minutes, 24/7. At this rate water useage is not an issue and I did away with the additional resevoir to feed the fogger chamber as it was leaking at the valve supplied.

Its an extremely dry fog, not what I expected. I can see some fine hairs and sideways roots developing. Plants are in veg and have been just topped for the third and final time.
I'm having some temperature issues and need to install an intake fan as the exhaust and circulating fans are not keeping up with the 2 digital lights even though they are set at only 300 w apiece right now.

 

[ttystikk]

The 90% RH for clones, 65-70% for veg and 40-50% for bloom thing is a little misleading.

First, rooting clones need high humidity so they don't dry out. As soon as the roots develop, start bringing that humidity down!

Second, the RH values for veg are good if your temps are in the low 70s, but a bit low if you're running temps around 80. For that temp, you want your RH values closer to 75%.

Third, run most of your bloom cycle with similar RH values as veg, and only drop them in the last couple weeks of flower.

 

[El Cerebro]

I'm struggling a little with this high rh in flower idea. Does burning sulphur really take the worry away at +70%? I'm a lot more comfortable around 50-60, but obviously that comes with opportunity cost. I wonder how significant?

Does this practice vary among us by region? I'm in the PNW, and have read some northeasters running much lower rh for fear of botrytis.

 

[Buddy Hemphill]

Never run sulpher in flower