This outstanding series from Thompson and Morgan has become one of my favorites. They are an interspecific hybrid between two digitalis species, which yields sterile hybrid offspring. This is great news, as once a foxglove flower is pollinated it generally drops it's flower. Since these can't be pollinated, the flower stays on the plant! They also keep on producing flowers over a long period of time. You can leave them in the field until you are ready to cut them, and simply clean off any older spent blooms.
These behave more as perennial than biennial for me. Perhaps since they can't set seed, they lack the trigger that they should die after flowering. I won't say they are a reliable perennial, but mine tend to bloom for 2 or 3 seasons. I've had them bloom in their first year from spring planting, and I've also had them wait until they've gone through a winter to flower. I suspect fall planting will yield flowers the following spring. I'm happy to be offering these at long last!