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

[Ray]

It’s all energy related.

When water evaporates, it absorbs energy, hence the cooling effect of a swamp cooler or LECA in a pot.

The greater the difference between the air temperature and the dew point, the more evaporation occurs, and like most everything it seems, it’s a gradient not an on/off thing. At 99% RH there is still some evaporation, it’s just so little that it doesn’t absorb much energy, so does very little cooling.

There are ways to compensate for that, though, such as increasing the air volume or surface area for evaporation (energy exchange) to occur. I’ve seen stand-alone swamp coolers placed inside of a greenhouse in Houston that were blasting out cool air, and that frankly stunned me (until I though about it…)

As to the original question about LECA ever truly drying out, I think the real answer is practically “yes”, but scientifically “no”.

If you have a wet pellet of LECA in an environment that is less than 100% RH, there is “room” for the water molecules in the air, so it will continue to evaporate, drying the LECA. However, every material has its own, unique affinity for moisture, in which the degree to which the overall system surface energy is lowered by being wetted is equal to the energy that would be consumed if the water evaporates. (Hence the difference between a cotton t-shirt that has a higher surface energy and one made from a lower surface energy “performance fabric”.)

[Shadeflower]

DC, that is interesting what you mentioned that you prefer lecca that doesn't float. Maybe lecca that floats sucks more moisture from roots than lecca that doesn't float.

But DC more importantly I don't think you use semi-hydro do you? I only use the airiest media is semi-hydro.

If using a regular pot you want the pot to be able to retain a bit more moisture between watering so you need something a bit more absorbent but in semi hydro it should be as airy to avoid too much algae. There will always be moisture in the pot.

I think it's good to just make these small observations - even if we all use different substrates depending on our preferences at the end of the day as long as there is a valid reason and logic behind it, its all about trying different things to find what the orchid responds best to.

[Ray]

Originally Posted by Shadeflower

DC, that is interesting what you mentioned that you prefer lecca that doesn't float. Maybe lecca that floats sucks more moisture from roots than lecca that doesn't float.

Very likely. These fired clay pellets are porous, but in some the porosity communicates with the surface and in others, it does not. In that latter group, those noncommunicating pores acts as flotation devices, and they cannot readily absorb water.

[WaterWitchin]

I only use LECA that floats, because it's my preference. I like that it floats, and purposely leave about an inch clearance at the top of the pot, so when I water the LECA floats up a bit, and believe it helps with aeration and debris flushing. The HydroCrunch I think is probably the most "floaty" LECA around. The difference between its wicking ability and others that are more dense, for me, is negligible and not worth paying attention since I like floaty.

Right now my grow space is running around 80-85% RH. When I water, the top layer of LECA stays wet for around three days, then with some top layer starts to dry and some not. Depends on depth of reservoir, height of pot, and how thirsty plant is. In winter when humidity sometimes hovers around 50% or so, the top layer is dry by the next day.

I've been spending time (too much probably) thinking about this recently since the using sphagnum with LECA thread lately. Been paying more attention this summer, as I'm attempting to grow my first catasetum. I realize I don't really pay much attention to a dry top layer of LECA anymore. The orchids don't seem to care either. Have never seen a new root stall out by touching dry LECA. Then again, I don't watch for it.

I guess it's all relative, but when I talk about raising the dry line, I'm not talking LECA that stays absolutely moist on the very top layer. Most of my pots have a dry layer after a couple or three days, depending on humidity and how cranked up I have the fan. I'm at the point where I usually water once a week, whether they need it or not.

[estación seca]

At 60% humidity my dry line drops far down the pot.

[DirtyCoconuts]

Shade- I have about 40 plants in SH. Maybe half indoors and in the patio. A lot of the bulbos in a modified SH using only #4 perlite and then about ten big guys outside in 1 and 2 gallon buckets

I tried a bunch of brands and buy 50L bags. If it floats I use it in mixed medium or as a top dressing on terrestrials

---------- Post added at 03:35 PM ---------- Previous post was at 03:33 PM ----------

I have algae in all my glass containers but none in the bucket due to the light or not

I have also been playing with GIANT hydroton for the reservoir area as it allows for more water and then the smaller normal pebbles are above to maximize the wicking.

[Ray]

Originally Posted by estación seca

At 60% humidity my dry line drops far down the pot.

That tells me the wicking rate of the particular LECA you are using is a bit on the shy side.

Originally Posted by DirtyCoconuts

I have also been playing with GIANT hydroton for the reservoir area as it allows for more water and then the smaller normal pebbles are above to maximize the wicking.

It isn't just the volume of the reservoir that matters, it's the height of it, and the available contact area of the LECA pellets that deliver the liquid upward.

I'd guess (and that is all it is, as I have not tested it nor done any calculations since I started drinking wine as I prepared dinner) that at a constant reservoir height, if the reservoir is filled with 1" spheres or 1/2" spheres, there would be more contact area among the smaller ones, making wicking better.

[WaterWitchin]

Originally Posted by estación seca

At 60% humidity my dry line drops far down the pot.

To what do you attribute that? Mine sure don’t.

---------- Post added at 03:59 PM ---------- Previous post was at 03:57 PM ----------

DC… speaking of that huge LECA, what’s your source for it please? Size?

---------- Post added at 04:01 PM ---------- Previous post was at 03:59 PM ----------

Originally Posted by Ray

That tells me the wicking rate of the particular LECA you are using is a bit on the shy side.

We cross posted Bill. I don’t think that much variation could be just poor wicking ability, could it?

[estación seca]

The only brand I have found locally is imported Hydroton.

[WaterWitchin]

What’s for supper and what’s the wine? Let’s take care of priority issues first!