Foxgloves

Autumn, once its cooled down and is damp, say late October (in the south of England, anyway, don't know where you live). They are biennial plants, so grow one year and flower the next.

As Bamboo says, they are biennials, but if you planted them out from pots in the spring they might be thinking this is still their first year. They will flower next spring, even if they are close together. Foxgloves will grow very well crowded together and in fact look even better in a thick clump.
Try also Digitalis Ferruginea, or d. lantana, or d.mertonii as these species are perennial and go on from year to year with little trouble. Seed is fairly widely available, especially from companies like Thompson and Morgan.