In your experience, what is the longest lived coreopsis cultivar in the upper midwest region - esp Zone 3b. I am looking for a coreopsis which may reseed, but the parent plant also continues to come up in the same location year after year.
My all-time fave is 'Moonbeam'. The lemon-yellow flowers blend well with my mostly blues and pinks and purples. I think it's hardy to zone 4 so you might be stretching the zone just a bit. It's lower growing than the other varieties. Not a self-seeder that I've seen but it's easy to divide and spread around.