On Thursday, 21 July 2016 21:43:50 UTC+1, Dave Hill wrote:

It's to shallow to allow much in the plant selection as it would dry out
very fast in summer and of course in wet weather it would get water
logged in no time

Thanks for your thoughts, Dave.

Being a fountain, both tiers are well-drained, so it won't get water-logged in the wet season. In the dry season the top tier shields the deepest part of the bottom tier.

So we're now thinking a large globular hemispherical sedum on the top tier, able to withstand hot, cold, dry, and wet. And on the bottom tier, vinca major or minor, which will dangle over the edges.

D.