As an experiment, I used lava rock to do what I called "volcano planting". My method was to dig out the hard, sandy, clay soil, and mix some of that back in with a palm/cactus mix, and plenty of lava rock. I formed that into sort of a cone shape in the planting hole, set the palm, then filled the hole with alternating laters of soil and lava, the top-dressed the planting with black lava to add some heat on sunny days. Since this was not a controlled experiment, all I can say is most all the palms planted this way continue to thrive, with the single exception of some Archontophoenix purpurea, which might have bit the dust from too much sun exposure at a young age, or not enough water. I planted Coccothrinax, spindles, and Rhopalostylis this way. Other palms planted in a more orthodox manner have done just as well, what can I say?

The red lava rock seems like it would be overly coarse for use in nursery pots, but the finer black cinders are great to promote fast drainage.

Only red was available of a larger grade which is why I will be breaking them up some. What are 'the black cinders'?

Red lava rocks are typically use as a top dressing instead of much. It could be used in the soil to provide better drainage. But there are cheaper rocks that will give the same benefit.

Black cinders are probably 1/8 the size of the typical red lava rock that is sold for use as an ornamental top dressing. If you've bought palms from Hawaii, they are often potted in this finer black, porous gravel.

It is much harder to find.

Hi
I use crushed black lava rock almost exclusively on epiphytic orchids you can find several grades of it at "Bushel stop" nuseries The advantage is that it's pH neutral doesn't decay, does not encourage weeds and costs about a third of "Leca" For terrestrial mixes I much prefer "Turface" Check out "Als mix" on the houseplant forum. for the various formulas. many people including me rave about them!! lol Love it for a general mix for palms
gary