Some species such as Ulex and Cytisus have large seeds with food reserves enough to last until the roots get down into the cooler layers.

Sand tends to hold moisture, and, if it is 'unwashed', from a river or quarry, will also have traces of silt in it.

Many plants produce wide root nets when grown in sand, or gravel, which gives them the ability to collect water and food over a large area.

Provided you don't have plants hurling seeds onto your sand, and you have, perhaps, removed the seed bank resting in the topsoil of your proposed garden area then you may be able to cut back on your weeding load. (Please notice all the hedgings and provisos I've put in!!!)

Of course, only those plants adapted to such an environment will prosper. Although not all alpine plants will grow in "pure" sand, remember that nearly all prefer the lean conditions that a comparative lack of nutrients provide, and of course, perfect drainage. And at the same time, alpines naturally grow slowly and are quite small by normal standards too.

Does the book give a list of suggested plants for the sand bed? I'll bet it includes a bunch of penstemon species. Grow most of them in good soil and all they do is flop around on the ground.

I have read a little on rock gardens. but I would think the plants are planted in the soil under the sand and grow up through the sand. although I may be wrong. I would think planting pregrown plants shrubs or trees in the soil under the sand would work for some plants.

My understanding of sand beds it that they are an environmental modification to allow people in areas with higher rainfall and humidity to grow plants from regions with more arid climates. I believe that you are even supposed to lay down a barrier between the sand layer and the native soil base to prevent worms and ants from introducing the soil to the sand. Soil plus moisture/heat and humidity = bacterial and fungal growth that can be deadly to many plants that need a more lean and dry growing medium.

As Leftwood suggests penstemon would be a fine choice of plant for this type of garden as would various cactus and other plants that hail from desert regions around the world.

I also don't know about sand being any more or less of a weed barrier. Here the weeds will grow just as readily in the sand as the native soil. Guess that's one of the draw backs to living in a desert.