I am curious if the lava rock sold for grill use can be used for orchids? It is expensive to by the nursery quality lava on line - those darn shipping costs.

My big box stores don't seem to carry much in the way of orchid mediums except for bark. I have purchased a Dend. that is considered to be an "lithophyte"

(growing on rocks) and I would like to pot it correctly for success.

Would like advice on this please?