L is for Lilac Sunday at the Arnold Aroboretum on Sunday, May 12, 2013. Lilacs are the only plant at the Arboretum that gets its own Day. Not only will there be music and dancing, family activities and vendors, Lilac Sunday is the only day that picknicking is allowed at the Arnold Arboetum. I have attended and it is a fabulous event. The Arboretum, as usual will be open from 10 am to 4 pm. It is best…