Hi David,
A good question which I forgot to address, even in part 2 posted today (16 July). When I first investigated building sand beds, the question of the depth of sand required was one I also asked . Every person I asked or reference I consulted gave a different answer - everything from "6 inches is more than enough" to "at least a couple of feet or deeper if you can"!
I decided that given the way they are meant to function, and the nature of alpine plant roots, I decided that I agreed with the "deeper is better" view. So in fact the sand goes all the way to the bottom of the beds (between 0.8 and 1.0 metre). At the bottom it sits on the native soil of the area. This depth means that the roots can usually access deep moisture even when the top few cm is completely dry and that watering of the beds is rarely necessary except that needed to establish new plants.
Cheers
Paul
