Kate, Cosmos! Why didn't I think of that. I have lots of different pinks and whites growing from seed. Poppies too! Doh! Perfect, they can just sit on top and waft about prettily until the end of the season, be pulled up, and then top dress and mulch the tulips underneath. You're a genius! 
Wintersong, I like the sound of that combination. The Aquilegia underplanted with the Lady's Mantle, and it's frothy, limey green-ness. Might steal that idea
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Inka, get your camera ready for that Tree Peony!
Yvie