S/H and Lava/cinder

[IdahoOrchid]

Has anyone ever tried lava as a growing medium for s/h? I know that in the smaller sizes there is the compaction issue, but what about the larger sizes? Has anyone ever at least done a wicking experiment?

I know that lava in my bonsai mixes sure helps keep the soil damp a lot longer than just bark does.

[Brooke]

I don't know if I would call this semi-hydro because it was just a "what if" moment I had.

I received a very large overgrown C. guatamalensis and divided it into two sections which were planted normally but had a third division with one pbulb with a leaf and 3 pbulbs with no leaves. The poor thing sat in a bucket of water for two nights and should have been pitched. I put it into lava rock, set the the clay pot in a plastic saucer and added an inch or two of fertilizer water to the saucer.

I still have the three bald pbulbs and one pbulb with a leaf but I also have a new growth starting, about 3" tall now and lots of new roots around it. Someday when I'm bored, I will inspect the roots and see what I actually have in all that rock.

I flush the pot once a week and replenish the saucer water. Does this even qualify as semi-hydro?

Brooke

[Ray]

Brooke - sure it is. You're just using an external reservoir.

Idaho - lava rock works OK, but I have a few concerns about its use as a potting medium: it does hold a lot of water, but a large percentage is in that coarse surface porosity. Being in large droplets right at the surface, the water can easily bridge the open spaces to clog air flow to the roots, so you need to use quite a coarse size to keep more open space, but that leads to poor capillarity. Secondly, studies (not mine) have reported that the stuff traps minerals and plant pathogens really well, degrading the overall conditions slowly over time.

You also have to be careful about the specific lava rock used, as some are relatively neutral, while others are quite chemically active, containing readily-dissolvable minerals that can poison the plant. That's definitely the case with ash clinker - it's usually loaded with soda ash.