Once gardeners know what's possible in their own flowerbeds, they can start to push the envelope. Boston lies in zone 6, but the Arboretum constantly tests species that are adapted to warmer areas, such as some hardy types of camellias. It does so not in response to climate change but as part of its mission to keep adding new plants to its collection.
"We always try to test the limits," says Dosmann. "All gardeners are in zone denial."