Roy, Allthough I am in a much milder climat (we get frost down to -8° 18F) I never put more then 2-3 cm (1") of soil on it. Otherwise the tubesr make a kind of "stem" to get to the surface. If any doubt put a good layer of mulch, compost etc on it I agree with John that C pseudibericum is a hardy and and most recommendable species. I grow it here like C hederifolium, but a dark pink mid winter flowering Greetings Lauw de Jager http://www.bulbargence.com/ South of France (zone 8 Olivier) Coord. Geogr.(GPS): 43°42' 43" N 4° 32' 12" E > C. pseudibericum grows well outside here and is seeding around > gently in the garden, so is certainly worth a try outside.