First Timer - water collection on leaves

Hello. This is my first grow and I have a couple questions that I'm hoping you pros can help me with.

I am using the BC Bloombox and I'm growing Lowryder Diesel. My plants are now in their 3rd week in the flowering chamber. I am using co2. A couple days after I turned on the co2, my plants really took off but now I'm noticing that a lot of the leaves from the middle of the plant to the top of the plant that are somehow drenched with water. It seems to be only with leaves that somehow got stuck to other leaves. I only have 5 plants in there but it is really bushy. I am trying to figure out exactly how the water is getting to those middle/top leaves. I do not foliar spray and it is a DWC setup. Has anyone ever had an issue with leaves somehow collecting water?

I was going to attribute it to the co2 as I modified the co2 line to stretch accross the canopy of the plants and I put holes in the co2 line to maximize how much co2 each plant was getting. The guys at bcnorthernlights seem to think the co2 modification is causing the wet leaf issue, but I'm looking to the pros for some more answers.

The last thing I want is to have a moldy crop and the humidity is now at 60%.

Any ideas out there? I'm sorry I don't have pictures.

Here is a quote from another grow site, although it's by a member (Earl) who is active here at RIU as well.


"I have gone into my grow room and been puzzled by a phenomena that I didn't understand. There would be water standing on a leaf that was under HID light and I was very bewildered why this was happening. I knew I had not allowed any water to spill on the plant, and I knew that my roof wasn't leaking, hell it wasn't even raining outside. So, where did this mystery water come from? Obviously the plant was transpiring water through the leaf and puddling on the top. But why? The answer is due to low vapor pressure deficit in my grow room.

If your interested in increasing your plants ability to grow in an enclosed environment, and you want to avoid diseases, and provide the best growing environment for your girls, then you need to be concerned about VPD.

So what is VPD?

Vapor pressure deficit, in ecology, is the difference between the actual water vapor pressure and the saturation of water vapor pressure at a particular temperature.

Unlike relative humidity, vapor pressure deficit has a simple nearly straight-line relationship to the rate of evapotranspiration and other measures of evaporation.

Plants lose moisture by transpiration from their leaves into the surrounding atmosphere.

The less moisture they lose, the more they like it.

We tend to think that the higher the relative humidity, the moister the air, the better it is for our plants, but that is only true up to a certain point.

What I am trying to show here is that relative humidity does NOT relate directly to the rate at which transpiration of water from the plant occurs.

Changes in relative humidity are not proportional to the rate of plant moisture loss."


I suggest if you are doing DWC you read the entire thread:

http://forums.cannabisculture.com/forums/ubbthreads.php?ubb=showflat&Board=24&Number=1354421&Searchpage=1&Main=157313&Words=vapor+pressure+Earl&topic=0&Search=true#Post1354421

Thank you shnkrmn! While I still don't exactly understand the underlying mathematics involved, I think you have pointed me in exactly the right direction! I knew there would be someone out there who knew what was up!

As soon as I removed my co2 extender tube, the humidity dropped from 61% to just over 40% and my temperature rose from 72 - 78 degrees. I think I'm finally in the right range!

Many thanks sir!

You are welcome. I guess your co2 could have something to do with it. I recommend again that you read Earl's hydro101 thread. Even if you are experienced there's a wealth of great information there. Good luck with your grow!

Hello there,

Thanks for the advice. I did read the article and it was great. I went back and read the information a little more carefully and I think I finally realize what was going on.

I used to keep an average temperature of 76-80/day and 68-72/night with a RH of 45-55. When I introduced the co2, my grow room temps actually dropped to 70-72/day and 65-68/night and my RH flew up to 60-63%.

From what I can gather (and i'm an idiot), I had 2 problems developing.

1. co2 is better used by plants at temperatures of 80-85 (some claim 90-95), so for one, I wasn't enabling my plants to fully utilize the co2.

2. by introducing the co2 which lowered my cab temp, I also affected the ability of the air to hold enough moisture to allow the plants to transpire (or is it persperate?). So at 70 degrees, with 60% humidity, my enclosed cab loses it's ability to hold anymore water vapor in the air which causes pooling of water on top and underneath leaves even with the HID on. There was just no where for the water to go.

Once I removed my co2 extender tube, the cab stays at 76-85degrees with the lights on and using co2. Almost within the hour my humidity went down to 55% exactly. I must say that if you follow the directions, and don't try and modify the cab, the bc northern lights bloombox is perfectly tuned. So far I have caused 2 issues because of my tinkering all the while thinking that I was doing something good.

My LRD have gone from 14 to 22 inches in only 7 days of using co2, so I want to keep it up

Again thank you and +rep to you!

"So far I have caused 2 issues because of my tinkering all the while thinking that I was doing something good."


That reminds me of someone's sig file on here: it reads "of course it's too complicated; I got high, I started thinking. That's what I do!"

Sounds like you are on the right track. Good luck and thanks for the rep.

Well it seems that the problem is getting worse now and I'm worried about powdery mildew hitting the plants.

I thought that it could have been VPD but it might be a combination of something else too. It seems that only the leaves that are touching other leaves are trapping water. So plant 1 has a leaf and plant 2 has a leaf...when plant 2's leaf sits on top of plant 1's leaf, it traps water from plant 1's leaf from evaporating.

So it seems like when two plant leaves lay on top of each other, the one on top stops the one on bottom from transpiring. It's like the leaves are stuck together and when you pull them apart there is water on the top of the bottom leaf.

I guess my plants are too close together but I can't move them at this stage without hurting the root ball.

I'll give it a couple more days to self-correct but I think I'm in for some long days of wiping off the leaves....what a pain!!!!

Ok well it seems the answer to my question is here:

https://www.rollitup.org/indoor-growing/33807-why-my-leaves-wet.html

Apparently it's just because the leaves are so tightly packed that one lays on top of the other and the one on the bottom can't evaporate the water so it just pools up on the leaf.

I still haven't been able to find out if this is a big problem I should worry about though. Right now I am opening the cab 2 times a day and running 3 fans for 30 minutes to try and help it evaporate by blowing the leaves off of each other. I really hate to do this though because I'm using co2 in the cab and each time I open the cab, I lose the co2 and have to manually add more with the over-ride switch to get levels back to 1200-1600ppm.

This wouldn't be so bad if I could find some smoke around here. It's been dry for weeks and I just keep drooling over my plants wishing they would hurry.... still another 3 weeks to go though....doh!

If I only knew if this is a precursor to mold or mildew....anyone?

You could rotate your plants every day so the same leaves don't end up stuck to each other creating an environment for mold. Natmoon's answer is a lot simpler than VPD and certainly plausible.

Thank you man! Unfortunately for my newb self, the plants are impossible to rotate because they have grown into each other so badly. I can't believe how bushy the DLR's are. I have at least 6 top colas on each plant, each one just as tall as the center. It's just a bit too hard to move around in my small cab.

I will definitely space my plants for my next grow so that they are easier to turn. Hell, I might even give it a shot now and if I break a few branches, oh well

Thanks again for the advice shnkrmn!