Japanese botanist Toichi Itoh was the first to successfully cross a tree peony with a herbaceous peony in the 1940s. It was an extremely difficult process, as tree peonies and herbaceous peonies have different bloom periods, and finding a way to successfully cross-pollinate them took many years. The initial successes did not grow into viable flowering specimens for more than a decade. It was not until 1964 that the first-named cultivars were patented—years after Toichi Itoh passed away.