Campanula (Bellflower) offers a bountiful crop in spring to early summer, filling the gap between early spring crops and summer annuals. Plants will produce flowers in the first year of production, if started early enough in the season. Plants should be started in fall, winter or early spring, as these daylength-sensitive plants require short days during seedling development to ensure sufficient stem length before flowering. In our Zone 5 winter tunnel trials, fall-sown plants overwintered well, blooming in early June on very tall, vigorous plants. In our Zone 5 spring tunnel trials, winter-sown plants flowered in mid-June through early July on shorter plants. Also known as Bellflower and Canterbury Bells.