In April you can start planting warm season annuals such as:

Impatiens, marigolds, petunias, sunflowers, zinnia, lobelia, allysum. Finish planting summer-flowering bulbs like tuberose, gladiolus, dahlias, and callas. And, plant chervil, coriander, dill, rosemary, and summer savory outside after the last spring frost date for your area. Your Extension agent should be able to give you the date.