Most bellflowers do best if planted in full sun, but will also thrive in light shade. Plant in moist, well-drained soil that is high in organic matter. Some are spreaders, especially clustered bellflower and Serbian bellflower, so plant these where they'll have some room to roam. But steer clear of the aggressive Korean bellflower (C. rapunculoides) which spreads so readily, it can become invasive.
Container plants can be set out any time during the growing season. Space most plants about a foot apart; the tall milky bellflower should have 24 inch spacing. Prepare the garden bed by using a garden fork or tiller to loosen the soil to a depth of 12 to 15 inches, then mix in a 2- to 4-inch layer of compost. Dig a hole twice the diameter of the pot the plant is in. Carefully remove the plant from its container and place it in the hole so the top of the root ball is level with the soil surface. Carefully fill in around the root ball and firm the soil gently. Water thoroughly.
Apply a complete organic fertilizer and a thin layer of compost each spring, followed by a 2-inch layer of mulch to retain moisture and control weeds. Water plants during the summer if rainfall is less than 1 inch per week. Deadhead flowers to neaten plants and prevent self-sowing. On taller types, remove faded flowers individually, then cut back the flowering stalks to the base when all bloom is finished. With low growers, wait until the first flush of bloom is past, then shear back plants by half. Peachleaf bellflower can self-sow to the point of weediness if not deadheaded. Most bellflowers benefit from division every 3 to 5 years to keep them growing vigorously.