Do You Have to Replant Sunflowers Every Year?

Annual sunflowers need to be replanted each year.

Annual sunflowers need to be replanted each year.

When you think of sunflowers, you're probably thinking of the large, happy yellow faces of the common annual sunflower (Helianthus annuus). Seen in many gardens during the summer, the annual sunflower comes in many different colors and sizes, and its seeds must be replanted each year. It is related to other types of sunflower that do not need to be replanted each year and that produce plants that are different from the annual varieties.

Annual Sunflowers

Annual sunflowers, which grow in most climates, come in a range of sizes. Small varieties, such as "Teddy Bear" and "Music Box," grow to just 2 to 3 feet tall, while giant "Mammoth" or "Russian Giant," can reach heights of 8 feet or more. Small varieties can be grown among other annuals in a small flower garden or in containers. The sunflower's compound blossoms measure from 5 inches across to as much as 12 inches or more. Each sunflower is composed of an outer ring of bright showy petals around a center of much small flowers called an inflorescence where seed production takes place. The seeds from larger varieties are an important food crop and also used to feed birds and livestock.

Planting Annuals

Annual sunflowers don't tolerate cold and should be planted only after the soil has warmed to at least 55 degrees Fahrenheit. You can also start them indoors in pots about six weeks before the last frost. Sunflowers do best in full sun, when the weather is warm, and in a spot sheltered from the wind. They grow in any type of soil as long as its pH level is slightly acidic to slightly alkaline, around 6.0 to 7.5. The seeds are large and easy to handle and should be planted from mid-April to late May in holes about 1 inch deep and about 4 to 6 inches apart. Larger varieties should be thinned to about 2 feet apart with rows about 30 inches apart and may need staking to prevent them from breaking under the weight of the flower heads.

Perennial Sunflowers

Perennial sunflower varieties, such as Jerusalem artichoke, also known as sunchoke (Helianthus tuberosus), and beach sunflower (Helianthus debilis), produce tall, bushy plants that produce many flower heads on multiple stems. Their roots systems are large and take up a lot of space, producing new plants and tuberous growths that can be harvested for future plantings and, as in the case of sunchoke, are edible. Because of the plants' aggressive growth and broad root expansion, they can quickly become invasive, so plant them in an area of the garden where this won't become a problem. Otherwise, all the tubers and root sections of a plant must be dug up so that they don't continue to produce unwanted plants.

Planting Perennial Sunflowers

Like sunchoke, beach sunflower is a spreading perennial with flowers composed of pale yellow rays around a smaller center that attracts birds and butterflies. Beach sunflower grows in U.S. Department of Agriculture plant hardiness zones 8b through 10, while sunchoke grows in USDA zones 3 through 10. Sections of tubers for planting should have at least two or three buds and should not be allowed to dry out before planting. Place them 3 to 5 inches deep and 15 to 24 inches apart in rich loose soil in rows that are 36 to 42 inches apart. Harvesting should wait until after the first frost, as the sweetness of the tubers improves the longer they are left in the ground.

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