When should I plant cool-season annuals?

FAQ
Question: 

When should I plant cool-season annuals?

Answer: 

Cool-season annuals are annual plants that prefer cool temperatures, growing best in spring or fall. Many are tolerant of a light frost often surviving down to 28°F or sometimes even 25°F with little damage to flowers or leaves. They are great additions to containers and garden beds in the shoulder seasons to add color late into fall or early in the spring season.

For the fall season in Iowa, cool-season annuals can be planted mid-to late September. For early spring color, plant cool-season annuals mid-March through early April, depending on the weather conditions. Some species do best when directly sown but many need to be started indoors and transplanted outdoors.If starting from seed indoors, consult the seed packet to determine the length of time from seed to transplant. For many annuals its 6 to 8 weeks. Count back from your projected planting date outdoors and sow seed at that time. For many species this means sowing seed in late July through early August for cool-season annuals planted in fall and mid-January to early February for those planted in early spring.