Good news, Jo Ann! Are the troughs made of tufa (carved out of natural rock, a specific type of limestone deposit) or hypertufa (a man-made mix of cement with other materials)?
You are in a much milder climate than here, and I imagine the trough dimensions are suited to your climatic conditions.
For people in colder zones, though, I would really recommend that troughs be deeper than the 5 inch depths described. In zone 3 and colder, many people would be taking the precaution of sinking shallow troughs like that into the soil for better "insulation" over the winter... which, to me, sort of defeats the purpose since troughs can otherwise be a very low-maintenance way of growing hardy alpines. (Extra fooling around is not of interest to me.
) This is especially a precaution for bowl-shaped troughs, since the soil is very thin around the edges due to the curvature of the bottom of the bowl. Just something for those in cold zones to consider...
