They grow wild here in the Stamford CT area in meadows and fields without care and bloom for weeks. Beautiful deep purple flowers that the deer ignore.. the plant could be grown for it's leaves alone..
I've been fortunate enough to stumble upon a clump of New York Ironweed in mid-September, growing wild here in the piedmont of S.C. I tried collecting seeds and planting with little luck. I've had good success with nursery plantings however.
Ironweed is also a great way to attract butterflies and another plus; they add great color late when not as many plants are still blooming.