The Livingston Seeds package said these flowers (Coreopsis lanceolata) would grow 1–2.5′ tall. An Illinois wildflower website describes them as reaching 3′. In their second year, almost all of my plants went well above that. Many got so tall that the plants fell over.
The tallest flower didn’t waver though, growing straight up to 53″. That is a lot more than 36″.
I feel like this extreme growth has something to do with how the plants took off this spring, when it was unusually warm and sunny. But it’s almost like their conditions are too ideal. I might need to collect seeds from the winning plant.