One of the tricky parts of gardening, is trying to find plants that will cover the leaves of spring blooming bulbs as their leaves and stems turn brown and die back to the ground. I've used Hosta and Hemerocallis with tulips. In one section of my garden, I have paired this giant Persicaria polymorpha with Allium. As you can see, it's not quite perfect - the Persicaria is quite successfully upstaging the Allium that aren't quite done. Although it really does hide the nasty brown leaves at this stage! I've also seen 'Anthony Waterer' Spirea used in a mass planting in Toronto with these giant Allium. In the boulevard planting on the fly it looked quite good - wanted to stop, but would have risked a collision if I had. Another suggestion I read about from University of Guelph was to pair Ligularia with these big onions. Their leaves would certainly cover the mess at the bottom and there would be no flower competition - as Ligularia have nice yellow or orange blossoms much later in the summer.