Break up the soil to a depth of 6 inches with a spade. Add equal parts sand and compost if you have heavy clay soil. If your garden is already sandy, just add the compost.
Remove the Serbian bellflower seedlings from their container. Tap gently on the bottom and sides of the container if the seedlings don't come out easily.
Dig a hole twice the size in diameter of the root ball and equal in depth to the top of the root ball. The plant will sit with the root ball top flush with the top of the soil.
Place the Serbian bellflower seedling in the hole. Fill in around the root ball with soil, and water it in.
Plant additional seedlings at least a foot apart as the plant spreads. Although this plant can handle some drought, keep the soil moist to help it get established.