Since a squirrel managed to climb five floors and eat my expensive tulips bar one 'Queen of the Night', the roof garden is rather devoid of colour at the moment except for these little beauties.
I bought this collection from Pottertons nursery a couple of years ago and they seem so happy baking in the summer sun (what little we had last year) on my roof terrace. It's actually quite a deep pan which allows their roots to go down among the grit and get moisture just as they would in the alpine setting they are used to. They were one of Valerie Finnis's favourites - she's one of my women in Gardening Women and a superb plant photographer - unlike me! - but I'm learning.