A couple of years ago I started to turn the floor of the old water mill into a scree bed. Taking the turf off revealed a floor that had once simply been beaten clay with broken brick and tile. So, no drainage. I considered that, with luck, relatively shallow-rooted alpines could grow in gravel above the old floor, and so far this appears to be the case. I’ve used pea gravel to a depth of between four and six inches, not mixed with any soil or compost. When planting, I take a fairly deep plug out of the clay, fill it with gravel, add a handful of compost, and plant to a depth where the neck of the plant will have plenty of gravel round it.
Results have been encouraging.
II work at trying to have colour in the scree bed throughout spring and summer. At this time of year, through to August, I rely on the South African rhodohypoxis varieties to give the colour needed to draw the eye. This (I think) is rhodohypoxis ‘Douglas’:
Rhodohypoxis are reliable here in Scotland, but the grassy leaves, followed immediately by the flower buds, push through the gravel quite late in April, so I have to remember where they are when weeding. Luckily, a nursery specialising in them is within range, so I don’t have to buy sight unseen. I note the Alpine garden society recommends covering them with a slate in winter to keep them dry, but I haven’t bothered to do this yet, and so far I haven’t lost any.
Gardening At The Edge 
I enjoyed looking into your Blog. This one on Alpines is nice. Have some here in the gardens too. I choose a new Blog every now and then and am putting your into my followers. Hope to see plenty of interesting photos of your area. For me it is most interesting to widen my appreciation of gardens in other places. Here at Lake Michigan it is beautiful, but so too in so many other places. I do enjoy. Jack
I have rhodohypoxis in a pot. they’ve been there for a few years, usually I put them in a cold frame but last year I forgot. they seemed to survive.