Questions about using lava rock

[AnonYMouse]

[Orchid Whisperer]

Thanks for the help everyone! I posed the same question on Orchidgeeks. So, the advice I am seeing, compiled from both forums, is:

There is not too much difference between the red & the black. The black could get hotter, potentially, in strong sun.

Prepare lava rock by rinsing thoroughly outdoors to remove dust and other fines (don't rinse in a sink).

Lava rock is probably best for plants that can tolerate drying between watering (Cattleya alliance, Epicats., Encyclia, some Dendrobiums, etc.), works well for plants that like to be mounted. Unless I can water daily, or even twice daily, it might not be the best choice for Miltonias, Paphs, and others that don't like to fully dry out.

Daily watering is needed as lava rock dries in hours. A top dressing of sphagnum may let me skip a day.

Use low TDS water (RO, rain, etc.), fertilize weakly/sparingly to avoid fertilizer/salt build-up, rinse and soak regularly to rinse out salt build-up.

[james mickelso]

There is a lot of variation in the texture of lava. The type I prefer is full of small holes ala swiss cheese. There is a lot of non porous lava out there which is just like any other rock. The type I use holds water for a day or more. Catts and their cousins really like it. Phals do well too but you have to keep them cool. As to lava absorbing minerals....??? I've had some small cats in lava for a couple years and never have seen any precipitate. Probably the most inert of media. Mix with sphagnum moss if it dries too quickly.

[Orchid Whisperer]

The lava rock I bought definitely has some holes. I will have a better idea about how "Swiss-cheesy" it is after I wash it.
Our local tap water is pretty good quality, typically TDS is near 100 ppm. I alternate between tap water & stored rain water, don't use much fertilizer, so I don't expect much mineral build up.

[james mickelso]

Here are three different types of lava rock. I collect my own but you can buy these different types. I like the more porous type as it holds more moisture but keeps it away from the root tissues. Keeps the media moist but not wet. I think the more dense type is just rock and you could use any kind of rock. The middle type is right in between. Characteristics of both.