Hardy annuals are slow to react to chilly temperature, remaining healthy and blooming into late fall. For some, even frost or a little snow doesn’t immediately send blooms wilting. The seeds of hardy annuals can be sewn directly into the ground in the spring as soon as the soil is workable. The flowers will seed during the season, the seeds will settle nearby, and then the seeds will grow the following spring. Include a thick layer of mulch, like 2 to 3 inches of leaf mold or pine bark chips, around annual flowers to retain moisture and warmth that can help keep the flowers blooming until evening temperatures start falling under 30 degrees Fahrenheit.
Alyssum (Lobularia maritima), also known as sweet alyssum, is an excellent ground cover. The slender leaves are barely visible beneath a mass of white, red or purple blooms. The plant grows to less than 10 inches tall. Plant in full sun to partial shade in USDA map hardiness zones 6 through 10.
Calendula (Calendula officinalis), also called pot marigold, produces yellow, gold or orange blooms starting in mid-summer. The plant grows 12 to 24 inches tall. Plant calendula in full sun to partial shade in USDA map hardiness zones 3 through 10.
Dianthus (Dianthus chinensis), also called China Pink, grows 6 to 18 inches tall. The blooms may be white or varying shades of pink. Plant in full sun in USDA map hardiness zones 4 through 8.
Larkspur (Consolidaambigua) grows up to 3 feet tall. Stems laden with white, pink or varying shades of blue flowers appear in mid-spring. Plant in full sun. Larkspur grows in most of the continental U.S. making it an easy to grow plant.
Heads of ornamental cabbage (Brassicaoleracea) may have white, pink or purple centers surrounded by light green to deep green leaves. Ornamental cabbage can be planted close together to create a flower bed border, or grouped together amidst other plants. The plant grows 12 to 18 inches tall. Plant in full sun in USDA map hardiness zones 7 to 10.
Snapdragon (Antirrhinum majus) grows 6 to 36 inches tall. The pink, yellow, white, red, orange, purple or pink blooms first display in spring. Plant in sun to partial shade in USDA map hardiness zones 4 to 11.
Viola (Viola tricolor) or Pansy (Viola x wittrockiana) are petite flowers-they grow less than 12 inches tall-that can be snipped for small vases or fancy toothpick holders. The blooms may be two or three colors of yellow, blue, violet or red and display starting in early spring. Plant in full sun to partial shade in USDA map hardiness zones 4 through 8.
Sources:University of Idaho Extension: Hardy, Semi-hardy and Tender Annuals
Iowa State University Extension: What is an Annual?
North Carolina State University Coop Extension Service: Calendula
Clemson University Coop Extension: Growing Annual
Viola vs. Pansy