Enjoyed your article but I don't see any mention of biennial Spiderworts. I posted a photo at http://davesgarden.com/community/forums/t/857480/ . This plant comes up only every other year and I wasn't sure what it was but it was ID'd as a Spiderwort. The Spiderwort files I see on DG all say perennial. Is the ID right? Are any of these biennials?? Thanks.
Todd - Many thanks for your reply. The plant is ready to burst into bloom so I will take a better photo when the flowers are out. Meanwhile, I will make sure to mark the spots where the plants are growing, and let you know next year if they come up again.