Butterflies are common in Knoxville starting sometime before April and going through at least September. A few may be present before or after that time.

Speaking of butterfly gardens, do you have Asclepias purpurascens in yours? If not, and you are interested in growing some, I collected a ton of seeds today. I'd be happy to let you have as many as you wanted. I also have a bunch of Iris domestica (aka Belamcanda chinensis) seeds. I've seen them listed as butterfly attractors too. I have Aralia spinosa (another butterfly attractor) seeds, but no one seems to want to grow it (maybe because it's very thorny).