We have a large bed of day lilies in the yard. They were there when we bought the house and actually appear to be the type you used to see by the side of the road – "tiger lilies". Once the flowers turned brown/fell off, I trimmed the flower stalks to make them a little neater looking. I did not trim the foliage. Now the leaves are turning brown and just look messy. They have never been divided…could this be the problem? Are they just over crowded?