Similar to daffodils, this foliage must be allowed to grow in the spring so that the bulb will have enough energy to flower in late summer. The picture below from a previous summer shows the motivation for putting up with the unruly foliage. The flowers that appear, seemingly overnight, are really lovely, especially when they are massed.
Last summer Jack and I built a little dry stream bed to allow for drainage through this area. In building the stream bed, we damaged and otherwise destroyed some of the lily bulbs, and I wasn't certain how many we would have this spring. But, as it turns out, we still have a fairly large number. When the foliage appeared, Jack asked me if I was going to take the bulbs out (as I threaten to do ever year). But I really do enjoy the flowers so I've decided to try to find a way to put up with the foliage.
After we made the dry stream bed, we planted some hostas along the edge of it. It will be interesting to see how well these rather small hosta hold their own with the lillies. I know that they won't hide the lily foliage, but I'm hoping they will provide something more pleasant to look at when the lily foliage starts declining.
Hopefully, the hosta will help, but they aren't a total solution. Just thinking aloud now . . . maybe I need to interplant something that would come up in the spring and bloom late spring to mid-summer? I have several purple coneflowers in that area and I usually have a lot of "volunteer" seedlings. What if I created a swath of coneflowers above the lily foliage? I wonder if I could manipulate the bloom of the coneflower by timing the cut-back so that I got a bloom flush both before and after the bloom of the lily? (Gardening experiments are so much fun and failure is rarely a big disaster!)
I'm sure other people have ways of dealing with surprise lily foliage, and I'd love to hear your ideas.