Just found this blog site that looks pretty good: http://lophophora.blogspot.com/2008_09_01_archive.html

About 3/4 the way down the page is a strombocactus growing on a rock. Has anyone ever done this? I wonder how you would do it?

Cool link mate, I'm intrigued by the Strombo on a rock too... there must be enough of a hollow in the rock to get some growing medium and roots in there.

CP

I'd say they use a similar technique to that employed in the mounting of bonsai on rocks - where no natural cavity exists, they've carve out one sufficient to hold the soil necessary to sustain a plant.

If there's no drainage provided it'd be a tricky juggling-act to keep the right amount of water up to the plant - it's definitely a project for the dedicated enthusiast.

Hey, look - three Tasmaniacs sitting on a post...

which one is which??

I shotgun Clyde