I just got back from Austin where my parents now live. As some of you may know, native soil conditions there are highly variable and some areas north of Austin (particularly west of I-35) have particularly miserable soil. My parents seem to have the worst of it though; their new house is built almost directly on limestone with no more than 1-2" of soil in some spots but many areas (40-50%) with almost no soil whatsoever. While it might be possible to do the conventional thing and bring in large amounts of loamy topsoil, it seems more likely that any soil we bring in to cover the rock will just wash away with even a light rain (in fact, I expect that's why the area is so exceptionally bare to begin with). HOWEVER, the good news is that it is possible (with some effort) to pick into the rock and dig small holes, in effect creating small beds where cultivation is possible.

Question 1: Looking at what we planned to do, it seemed to me that this is similar to container cultivation in certain respects. I have some experience with 5:1:1 mixes (many thanks to Al's posts) and I was wondering if it might be best to employ something like that for our unconventional in-ground planting. I know the general thought is that container planting is essentially hydroponic and that in-ground planting is a whole different endeavor, but our unusual circumstances mean that plant roots may able to sneak into holes in the rock but the roots will be largely confined to the excavated area. The rock is porous enough that it should drain rather quickly.

Question 2: We're planning on introducing drought-tolerant native perennials, but their summer weather is fairly hostile... assuming some agreement on the above, any ideas on whether using turface in place of perlite might help in the wilting summer heat? I've seen recommendation of a 5:1:3 mix when daily watering is not possible. Would that work here?

THANKS for any advice/info.