How do you maintain humidity in dry areas?

[Simplicio]

I've bought about 2 dozen different humidifiers.
Top fill ultrasonic is by far the best. They blow out a dense fog that can raise humidity a lot when it evaporates.
Evaporative humidifiers can't keep humidity very high, but the fog from enough ultrasonic humidifiers can.
If the humidifier blows fog into the tent from outside the tent, so that the heat it produces doesn't get in the tent, then the humidifier will cool the tent a few degrees F as the fog droplets evaporate and absorb their heat of vaporization.
Usually a supplementary fan is needed to blow the fog into the tent and disperse it.
Humidistats aren't very accurate, and tent humidity doesn't change very fast, so I control mine manually.
Temp can change fast, and thermostats are accurate, so a controller is useful with a heater.

 

[Olderfart]

Thank you all for the wealth of information! I really appreciate it and am going to use some of this as I get closer to flower.

@Olderfart - I think I'm going to start here. I've read this trick before but had no idea you could net so much extra humidity out of it. It might actually end up being too much, so I may not be able to sustain it -- but am definitely going to give it a shot since it seems like the simplest to implement and maintain.

@Mañ'O'Green - I'll look into snagging one of these if the above doesn't work. My main trouble came around the time I hit flower, but I was dealing with stunted plants and chronic underwatering. I think both contributed to my dryness issues. This time around, I have 4 plants in there. Provided they keep growing well, I expect humidity will be a fair bit higher without further intervention. Otherwise, I definitely like the idea of a larger evaporative unit (particularly with a filter) elsewhere in the lung room.

@FTF_damien50 - Thanks for this tip! I will make sure to take this into consideration if I purchase one. Seems like simpler is better in this case. I do track VPD. So far, I am doing well; but it all falls apart once I have to start running exhaust. I think there were a lot of contributing factors to that last run though, so hoping some of these adjustments can raise my baseline and keep me in a better place for the whole cycle.

Thanks again!

There is no problem with too much humidity, just expose less towel. You want a fan in there anyway, so pointing it full blast at the towel fetches the water as well as circulating air in the tent. Works a treat, and unlike the misting humidifiers, it does not need distilled water, and it doesn't cover your plants or bud with dust from the water hardness ingredients.

As @Simplicio mentions, RH doesn't tend to change quickly, so manual adjustments work fine. I had no trouble keeping my grow in the VPD zone with manual adjustments to ventilation and the towel/fan when I was using it. Once the plants got big, they pretty much did all the humidification needed. The autopots keep the pots well watered, so the plants never stop transpiring lots if the temp is right, and my 2x4 got pretty much plugged with three plants.

Oh, I forgot to mention, I used a full sized terry towel, and that may have helped with how much RH I achieved. The extra surface area of the terry cloth probably helps with evaporation. I expect that using a smoother and smaller tea towel might not work as well.

 

[olegren]

@FTF_damien50 -- It does indeed. I have a CloudInfinity 6". It has 10 speeds. I don't think I've ever run it beyond the third setting. Right now I only have it on the first in that 5 off/2 on cycle. I oversized exhaust so I could get something that would hopefully run pretty quiet all the time.

I'm looking back through historical data now. My highest temp was 91.6F and RH bottomed out around 25.2%. My plant was pretty stunted, humidifier ran out, and lights were cranked. And I'm 90% sure I was chronically underwatering.

In general, I think I could keep around 50-60% with another humidifier or the towel solution -- which would be right around where I would need it to be under the same (admittedly hot) circumstances. I might still move that driver out of the tent. That will help keep temps down a lot when it's full blast.

@Simplicio - Thank you! The unit I have in my tent is an ultrasonic, too, and I really like it. It's just a little more overhead than I'd like. I have been reluctant to run multiple units because of the logistics of keeping that much distilled water around, but it may still come to that. I have been looking more at the ones with filters, too.

I actually tried setting mine up outside the tent and keeping that room closed off most of the time. It helped but just not enough. (Didn't quite get 7% raise in ambient RH with the thing running constantly) So I moved it back in, and it does a great job without adding much heat -- so long as I am not running exhaust. With exhaust on 24/7, you can practically watch the fog travel a route from the nozzle into the exhaust.

@Olderfart - Do you end up having the fan blow into the towel and away from plants? Or is it okay to let the fan blow at the towel which might be towards the plants as well? My only concern here would be the hard water remnants being flung off.

I love this solution. I had read about it before and am not sure why I never tried it, but the boost you're talking about sounds awesome. I have a fan oscillating in there already -- and another clip on that I think I'll point at a small towel to test this. Even better that the size/configuration of the towel can serve as a mechanism to adjust.

Thank you all!

 

[Olderfart]

@FTF_damien50 -- It does indeed. I have a CloudInfinity 6". It has 10 speeds. I don't think I've ever run it beyond the third setting. Right now I only have it on the first in that 5 off/2 on cycle. I oversized exhaust so I could get something that would hopefully run pretty quiet all the time.

I'm looking back through historical data now. My highest temp was 91.6F and RH bottomed out around 25.2%. My plant was pretty stunted, humidifier ran out, and lights were cranked. And I'm 90% sure I was chronically underwatering.

In general, I think I could keep around 50-60% with another humidifier or the towel solution -- which would be right around where I would need it to be under the same (admittedly hot) circumstances. I might still move that driver out of the tent. That will help keep temps down a lot when it's full blast.

@Simplicio - Thank you! The unit I have in my tent is an ultrasonic, too, and I really like it. It's just a little more overhead than I'd like. I have been reluctant to run multiple units because of the logistics of keeping that much distilled water around, but it may still come to that. I have been looking more at the ones with filters, too.

I actually tried setting mine up outside the tent and keeping that room closed off most of the time. It helped but just not enough. (Didn't quite get 7% raise in ambient RH with the thing running constantly) So I moved it back in, and it does a great job without adding much heat -- so long as I am not running exhaust. With exhaust on 24/7, you can practically watch the fog travel a route from the nozzle into the exhaust.

@Olderfart - Do you end up having the fan blow into the towel and away from plants? Or is it okay to let the fan blow at the towel which might be towards the plants as well? My only concern here would be the hard water remnants being flung off.

I love this solution. I had read about it before and am not sure why I never tried it, but the boost you're talking about sounds awesome. I have a fan oscillating in there already -- and another clip on that I think I'll point at a small towel to test this. Even better that the size/configuration of the towel can serve as a mechanism to adjust.

Thank you all!

I had the fan blowing away from the plants toward the corner with the bucket of water, but that was just a matter of that being the easiest to set up given the size of my pots. I doubt that you need to worry about the towel releasing dust. The air speed involved is low, and most of the towel surface will be moist so would not shed anything. In any case, if super small particles were released, I imagine that they would be flying around in the tent no matter which way the fan was pointed.

I was actually very surprised at how much difference in RH this approach generated. I was expecting to maybe raise it by 10% if I was lucky, nothing like the 20-30% lift that I had. I will be interested to hear how it works for you.

 

[Death The Cultivator]

You could try extracting more heat with a higher fan speed but like MoG said, issues arise below 40% and there is roughly a 15% decrease in RH from seed to harvest.

Another question, do you pack your tent with plants? RH is always better with more plants one. Also do you have an IR thermometer? Ambient temperature will be different than leaf surface.

The 6 gallon Aircare unit I have will humidity the whole 4x4 to 70% but my average RH is 40% to begin with. After a day or two the whole room will be humidified and windows covered in condensation then the tent starts getting into the 80s and low 90s.

I don't have a solution but I'm thinking of using the humidifier in the exterior room just to keep RH around 50-60 since I dry in that room as well. An extra humidifier in your lung room might be the best idea.

 

[olegren]

@FTF_damien50 - Great stuff here. Thanks! Raising exhaust is always an option, but as you pointed out that hoses my RH. Then again, I guess it would’ve helped when I hit those extreme conditions since ambient RH was higher than in tent.

to your point — I do have an IR thermometer. Forgot to check that during extremes. Today though I’m at 82F in tent but leaves are averaging about 76. I keep forgetting to use that temp for VPD purposes. This is a really good callout.

also, I have 4 plants going this time. I am hoping that will help the overall situation. Previously I had two at most — and they were mostly under watered.

If towel trick doesn’t get me there, I think I will grab another decent ultrasonic humidifier for my lung room and aim for about 10% boost. That would get me where I need to be. Going much higher than 50% could be bad, as I have a lot of electronics near my grow area.


@Olderfart I will let you know! Planning to get this set up shortly.

 

[Olderfart]

Hey @olegren, good luck with it.

Your leaf temperature is lower than I would have expected - perhaps I need to actually measure mine next time around... When I was using my VPD charts last winter, I just assumed that the difference was something like the 2C that seems to be common. I have an IR thermometer, so this winter I will check.

 

[olegren]

@Olderfart - I ended up checking my leaf temps later than afternoon, and it was much closer - like 78 average. Not sure why I saw it wander up; although the ambient temp outside the tent was probably a couple degrees lower that morning. (Temps in the tent were the same though which is confusing)

Since I was able to babysit, I am experimenting with the towel trick today. So far, the results are really exciting!

I was averaging around 71% RH earlier today with typical setup: Humidifier on inkbird, exhaust on lowest setting and on 2/off 5. I had a tray of water in there because I wanted to see what that would do in terms of slowing humidifier's emptying. Temps were 83.3F.

I ended up shutting off the humidifier, hanging a towel over the tray (I dipped it first and left one end in), and turned exhaust on 24/7 at setting 1. An hour later, things landed right around 67% RH and 81F.

Ramped exhaust up to 2, humidifier still off, and we are at 79.9F (it's still dropping a bit) and humidity seems to have stabilized at 61.4%.

I'm curious to see how long the towel will last. I just filled a seedling tray with water and left one end of the towel in, so it should soak up the rest. Might swap it out for a bucket or something if it dries out fast. Anyway, this is a huge win. I can sustain this very easily during flower if nothing else, and it will save me about $1 a day. Thanks again for mentioning it!

 

[Olderfart]

@Olderfart - I ended up checking my leaf temps later than afternoon, and it was much closer - like 78 average. Not sure why I saw it wander up; although the ambient temp outside the tent was probably a couple degrees lower that morning. (Temps in the tent were the same though which is confusing)

Since I was able to babysit, I am experimenting with the towel trick today. So far, the results are really exciting!

I was averaging around 71% RH earlier today with typical setup: Humidifier on inkbird, exhaust on lowest setting and on 2/off 5. I had a tray of water in there because I wanted to see what that would do in terms of slowing humidifier's emptying. Temps were 83.3F.

I ended up shutting off the humidifier, hanging a towel over the tray (I dipped it first and left one end in), and turned exhaust on 24/7 at setting 1. An hour later, things landed right around 67% RH and 81F.

Ramped exhaust up to 2, humidifier still off, and we are at 79.9F (it's still dropping a bit) and humidity seems to have stabilized at 61.4%.

I'm curious to see how long the towel will last. I just filled a seedling tray with water and left one end of the towel in, so it should soak up the rest. Might swap it out for a bucket or something if it dries out fast. Anyway, this is a huge win. I can sustain this very easily during flower if nothing else, and it will save me about $1 a day. Thanks again for mentioning it!

Woo hooo! Towel for the win. Really glad to hear that the towel and fan worked for you my friend. It seems to be all my operation needs...

 

[Vegasbear87]

The area where my tent's at stays in the low 40% range in terms of natural RH. I remedy this in my tent with a humidifier. That works just fine in the early stages where I don't need airflow constantly. I have a timer cycling exhaust 2 minutes every 5 minutes, and the humidifier is set with an inkbird to kick in when it drops below a threshold. The lights are dimmed fairly low, so heat from them is negligible.

But when things start to stink, I need to go to exhaust 24/7; at which point humidify goes sideways fast. The humidifier naturally wants to run all the time, and I just can't keep enough distilled water on hand to keep it going. What humidity it cranks out is going straight out the exhaust. Heat compounds the problem. My Meanwell driver is currently mounted to the back of my QB heatsink. On full blast, it raises temps considerably.

I have read a lot of advice suggesting to instead raise the RH in the 'lung' room -- and in turn the ambient RH will be higher; at which point it naturally follows that the tent will benefit from the same.

So, for those of you in dry areas, how do you accomplish this? A larger whole-home unit? Multiple smaller units? I can only imagine the headache associated with keeping something that large stocked with distilled water. I feel like I must be missing a good solution here. Does anyone have any advice?

Thanks!

I live in the Mojave desert, and when my plants start to get bigger, the tent maintains an RH of around 50-60% at all times. I only run a humidifier during the first couple weeks of veg. Seems to equalize itself about 1/3 of the way through a grow.

I use a one-gallon ultrasonic humidifier with RO water, lasts approx 24 hrs set at 50%. Not sure what else you can really do without upping your size.