If the RH is above 50% will LECA (and terra cotta) ever truly dry out?

[DirtyCoconuts]

Originally Posted by Ray

It’s not so much the mineral deposits as it is the porosity of the LECA, and that’s mostly an issue to the surrounding environment.

If the LECA is quite dry, it can literally desiccate a root tip that comes in contact with it.

Ray intrigued me with this comment - i want to know if the RH is above 50% and i soak a pot or a leca pellet in rain water, without heat or sun being applied, will that clay ever truly dry out or will it stop drying once it is as wet as the air?

[Clawhammer]

I keep my rh at 80% in my growroom and dry LECA still seems dry to me.

Thats my completely unscientific and unmeasured contribution lol

[rbarata]

Evapiration happens always unless RH=100%.
Dependinf on the RH value, it' the evaporation rate that changes.

[Shadeflower]

yeah it does and the problem Ray mentioned isn't so much that a dry surface is no good for roots, it's that lecca sucks additional moisture from roots. This is why I have stopped using lecca as a top layer. I use it where it is humid and cover it in pumice which is safe to dry without damaging roots.
I was going to mention something that I have noticed. All my good substrate floats. If it floats it means it is airy. And that is what we are aiming for. Lecca floats, pumice floats, bark floats, perlite floats.
I mentioned recently how pumice is not all the same, it's a natural product that varies in consistency so a very simple way to check if pumice is airy enough is to do the float test. If it floats it is good to use.

I used to not do the float test but I've recently noticed that would lead to more algae so pretty much any substrate I use these days should float. If it doesn't float then it isn't airy enough. That's my latest conclusion.

I know lecca floats so is airy but it does dry roots excessively. It's just a flaw to lecca one should be aware of. Ray said his solution was to keep the lecca wet all the way to the top but that would create too much moisture in the bottom for me so I use a different top layer instead.

[DirtyCoconuts]

not all leca floats.

and i am wondering if the gradient reaches EQ at any point above 100 RH?

i look for only the LECA that does NOT float as that hugely disrupts the pots when i water them. I find hydroton the best and it barely floats at all

in my experience i find that the surface and the inside of the leca are not in perfect balance and that the center retains moisture longer ( from breaking a few to test this premise)

I use a lot of off brand leca in my medium and as a medium for various plants (as well ass many plants in clay pots) and the roots love the clay. i have never seen any roots die from touching any of the clay surfaces and, in fact, they all seem to accelerate once they touch it. I have several Catts in clay pots with no medium and no desiccation which makes me wonder why?

my hypothesis was that the humid air was keeping the clay from ever fully drying

[SouthPark]

Originally Posted by rbarata

Evaporation happens always unless RH=100%.
Depends on the RH value, it's the evaporation rate that changes.

True ------- so altogether, it will be a consideration of the system as a whole ----- evaporation rate (linked to relative humdity), wicking behaviour --- which could also involve average rates, and anything else we add that has some significant effect on the amount of water in the leca at the various layers of it.

[DirtyCoconuts]

Also, if evaporation happens at all RH below 100 then why do swamp coolers and misters become ineffective at rates lower than 100?

[Clawhammer]

Wet-bulb temperature - Wikipedia

Interesting read

[estación seca]

Swamp coolers become relatively ineffective when dew point is above 55 F / 13C. Dew point is calculated from temperature and relative humidity. Swamp coolers will still evaporate some water when the dew point is above 55 F but not enough to make much difference.

For example, the National Weather Service (link in my signature block) says this is for Phoenix right now:
Mostly Clear
106°F
41°C
Humidity 18%
Wind Speed N 0 MPH (0 KPH)
Barometer 29.76 in (1007.79 mb)
Dewpoint 54°F (12°C)
Visibility 10.00 mi / (16.6 km)
Heat Index 105°F (41°C)
Last update 29 Jul 04:20 PM MST

My evaporative cooler is cooling my sunroom.

Water can evaporate into saturated air when energy is added. You can boil a pot of water dry during a hurricane (if your stove works.)

[DirtyCoconuts]

ES. That was my original caveat about unless heat or sunlight is added

I read the wetbulb thing prior to posting and that is what led me to post the question.

What I am still confused about is that the leca drying by evaporation is also going to cool it. This would then slow its evaporation and (I surmise) create a point, either in the SH pot or in the ambient air, where they leca will no longer give its water up bc there is no ‘gradient’ between the leca and the air.

I am not really sure how to test this…. Maybe a good scale and I could weigh them daily until it stops drying out…