Gerald L. Klingaman
Plant Common Name
Plants in the genus Helianthus are commonly called “sunflowers” for their large, cheerful daisies that track the sun. There are around 70 species in this genus. They are naturally distributed across North and Central America and grow in a wide variety of locations, from open sunny meadows and uplands to boggy areas and swamps. In the garden, they are grown for their showy flowers; the most common species being the annual sunflower (Helianthus annuus), which is also grown as a crop for its tasty, oil-rich, seed.
Helianthus are most commonly tall, herbaceous and may be annual or perennial. Some have single stems, while others form multi-branched clumps. Likewise, some have tuberous roots, some fibrous and others spread by rhizomes. Leaf shape is highly variable. The lower leaves are often opposite to each other and heart-shaped, while the ones on the upper part of plants tend to be narrowly triangular and alternate. Some have lobed or very linear leaves. The foliage is usually green, rough to the touch, hairy or sticky and dotted with oil glands.
Sunflower daisies generally appear from late spring to frost, annual forms can bloom at all times and perennial forms tend to bloom from midsummer to fall. They may be produced singly or in loose groups. The large, round eyes are comprised of lots of small disc flowers that may be yellow, green, red, brown or purple. These are surrounded by single or multiple rows of pointed petals (ray flowers) which are usually yellow and occasionally white, orange, red, or burgundy. Bicolored flowers are also available. Sunflowers draw bees and butterflies and their seeds are revered by many mammals and birds.
There are many garden-worthy Helianthus. The easy to grow sunflowers we all know and love are mostly Helianthus annuus varieties. In summer, these tall (sometimes enormous) plants produce huge daisies that come in lots of colors and produce lots of edible seed. The big, bold willowleaf sunflower (Helianthus salicifolius) is a tall, airy perennial common in prairies and areas with limestone bedrock. It is a tough plant that will withstand hot summers and drought. Beach or cucumber sunflower (Helianthus debilis) is an herbaceous annual or short-lived perennial with buttery yellow blooms, and the pretty, golden-flowered Jerusalem artichoke (Helianthus tuberosus) is grown for its tasty edible tubers.
Sunflowers are generally very easy to grow, though hardiness and culture are species dependent. Most are drought tolerant and prefer sunny locations with fertile to average soil that’s well-drained and neutral to alkaline. Garden varieties appreciate occasional applications of water. Most Helianthus gently self-sow, so it’s a good idea to leave some mature seedheads at season’s end.
Plant sunflowers to add a bold presence in the garden. They provide a quick, though short-lived, screen and sunny blooms. Children love to grow the annual types because they flower quickly. There are many dwarf forms even better suited for children's gardens. Be sure to include some Helianthus to butterfly gardens; adults visit the blooms and the caterpillars of some species feed on the leaves. Annual sunflower blooms are spectacular for summer cutting—think of Van Gogh’s immortalized "Sunflower" paintings—and should be planted in spring, early summer and late summer for season-long blooms.