Buy healthy, green plants with no signs of wilting or disease.
Plant in spring in neutral to acidic soil (soil with a low pH). If your soil is too alkaline, work in a little garden sulfur.
Keep soil evenly moist. Mulching is a good idea.
Trim faded flowers to promote longer bloom.
Fertilize every four to six weeks or work in a slow-release fertilizer (or plenty of compost) at planting time.
Tear out and discard plants in fall, after frost fells them, or when they become ragged-looking.