What benefit is there to adding LECA to a bark mix?
 

For those who don't know what LECA means, it is an acronym for Lightweight Expanded Clay Aggregate. It was initially developed as a concrete additive to improve concrete's abysmal insulation value. LECA is inert, pH neutral, and due to its moisture wicking capability and gas permeability it has been adopted for use with orchids.

Okay, the question. I've noticed the some commercial greenhouses mix LECA into their potting media. In this thread I'm asking "why?".

-Keith

I'm guessing because it doesn't break down, and the bark does, it lets them stretch repotting intervals. I no longer use bark. I repot almost everything into straight LECA. I'm still working, and there are times I can't get to repotting when a plant in bark needs it.

I suspect that LECA in a bark mix is doing the same thing that pumice or perlite or any other inorganic is doing - opening up the mix somewhat more, and also tending to keep it aerated over time as the bark breaks down. My guess is that which inorganic material is used depends on what is most available for the least money in a given location.

^^agree with above answer. Lecca is cheap and adds aeraetion. In small quantities it will not change how to water bark much at all. so easy cost effective way to bulk out the pot a bit. I like adding lecca at the bottom and bark at the top. lecca dries faster than bark and lets more air in at the bottom. This prevents water pooling at the bottom too much.
I originally started using lecca just to save on potting material but it adds a lot of aeration.

Realize layering two distinctly different media in a container creates a barrier to water passage at the interface. The bark above a layer of LECA might stay wet longer. Layering potting soil over a layer of gravel for a standard house plant most definitely leads to worse drainage of the potting soil, not better.

I use LECA is almost all my mixes to increase aeration. There's some water wicking effect that under my conditions it's neglectable as it dries too fast.
For rupicolous, I use only LECA with a sphagnum layer at the bottom. Under these conditions I water everyday in summer and every two days in winter.

Hey e.s., how does not having to repot compare with having to water more frequently? That's my perception with LECA, anyway.


-Keith

---------- Post added at 02:56 PM ---------- Previous post was at 02:53 PM ----------

This is definitely an interesting idea. With the sphagnum on the bottom, it will be easy for it to become saturated. The end result would seem to be a sort of semi-semi hydroponics.

-Keith

The sphagum layer at the bottom acts as a water/humidity reservoir that keeps the pot hydrated and prevents temp build up inside the pot.

Very true which is why lecca is used either in hydroponics or semi-hydroponics.

Otherwise it dries as fast as a cork mount.

Still doesn't stop people growing on cork mounts so to some that would be a mute argument.

I am with you though, to me watering less and getting the same results is my aim.

Orchid nurseries have big automatic watering systems.

No need to ever worry about a substrate drying out too much ;)

As far as I can tell that is a myth.. If you use bark on top of a solid layer of coarse leca the bark dries faster not slower, assuming you use a proper orchid pot with good drainage then the leca allows aeration at the bottom of the pot. It's easy to see with clear orchid pots as well.

I don't know where this myth comes from, no doubt it has some foundation, yet it doesn't make sense. If the medium is coarse and actually allowing air movement why would it retain moisture longer? Try it for yourself and see. Take two clear orchid pots, put a leca or coarse gravel drainage layer in one with bark on top and just bark in the other. Soak them down and then let the dry. When I did it the leca dried more evenly and quickly.

The only way this story makes sense is if you are mixing many sized media, including very small sizes together and the result is the coarse layer gets thoroughly clogged, which seems unlikely with orchid bark. Imo as long as the particle size of the bark and drainage layer are similar it shouldn't be a problem. My happiest plants are potted like this and I'm slowly migrating all my plants to this style.