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Missouri Environment & Garden



AUTHOR

David Trinklein
University of Missouri
Division of Plant Sciences
(573) 882-9631
trinkleind@missouri.edu

In Celebration of Sunflowers

David Trinklein
University of Missouri
(573) 882-9631
trinkleind@missouri.edu

Published: May 7, 2021

yellow flowers with orange centers

According to Greek mythology, the water nymph Clytie fell in love with Apollo, god of the sun. Apollo, who was thought to have a palace in the east, dazzled the earth each day as he drove his golden chariot pulled by four fire-breathing horses through the sky from east to west. Ultimately, Apollo rejected Clytie's affection which nearly drove her mad. Heartbroken, Clytie spent nine days without food and water searching the heavens, waiting for Apollo to appear. Ultimately, Clytie was transformed into a sunflower—a plant which turns its face towards the sun as it moves across the sky each day.

While the ancient Greeks might be accused of having vivid imaginations, they were observant when it comes to sunflowers. Young sunflower plants do follow the sun in an attempt to intercept as much light as possible for photosynthesis. The phenomenon is known as heliotropism and is due to the action of sunflower's internal (circadian) clock acting on growth hormones that cause cells on different sides of the plant's stem to enlarge or contract. Older sunflowers face mainly east in an attempt to allow flowers to warm earlier in the day to attract pollinators.

yellow flowers with orange centers

In honor of this unique plant, the National Garden Bureau has chosen sunflower as its annual garden flower to promote this year and has declared 2021 to be the "Year of the Sunflower." If every there was a garden flower that promotes self-confidence for the novice gardener, it has to be the sunflower.

Annual sunflower (Helianthus annuus) is a member of the Asteraceae plant family and is thought be native to the Americas. Members of this plant family bear compound inflorescences botanically classified as heads. The latter consists of a tightly-packed cluster of small, tubular disc florets surrounding by one or more rings of ray florets. The disc florets are the primary producers of seeds for members of this family, while the ray florets (often erroneously referred to as petals) mainly attract pollinators.

Sunflower is native to the Americas and is thought to have been first domesticated nearly 5000 years ago in what is now Mexico and the southern reaches of the United States. Native Americans of that era grew them for their edible seeds, which remain excellent sources of several nutrients, including protein, vitamin E and selenium.

Sunflower was introduced into Europe in the early 16th century and soon made its way to Russia where its cultivation for the production of sunflower oil originated. Russia soon developed a thriving sunflower oil industry, which made its way to North America in the mid-20th century. Indeed, some varieties of sunflower (e.g., 'Russian Mammoth') pay homage to the importance played by the Russians in the development of this crop. Shortly after reappearing back in North America, new varieties of sunflowers were developed, mainly for oil and seed production. Today, although it is still considered an alternative crop by most, American farmers produce nearly three billion pounds of sunflower seeds yearly.

yellow flowers with orange centers

Teddy Bear

Although sunflower has long been grown as a novelty in the garden because of its towering stature, it was not until the late 20th century that varieties were developed for their ornamental appeal. An early example of the latter is the variety 'Teddy Bear,' which produces fluffy, golden pom-pom like flowers six inches in diameter on plants only 24 – 36 inches in height. More recent introductions include All-American selection winners 'Soraya., 'Ring of Fire,' and 'Suntastic.' All are relatively dwarf, free-flowering and suitable for the garden border or as cut flowers.

yellow flowers with orange centers

Soraya AAS Selection program

There are several different methods of classifying sunflowers, such as single versus branching. Single stem sunflower varieties are best for high-density plantings and produce consistently beautiful flowers on tall stems. Succession planting is needed for continuous blooms throughout the season. In contrast, branching varieties produce flowers on multiple shorter stems throughout the season, resulting in sunflowers all summer long.

Another classification method revolves around the production of pollen. In an era when pollinator preservation is being emphasized, pollen-bearing varieties represent a good option for gardeners wanting to support the cause, but on a limited budget for plant material. Pollenless sunflower varieties were bred to be male sterile and, hence, pollen free. The latter trait makes them more ideal as cut flowers, since pollen that would fertilize the florets is absent, thus extending the life of the flower.

yellow flowers with orange centers

Ring of Fire AAS Selection program

Whatever the type chosen, sunflowers prefer a full-sun location. Because of their deep tap root, a well-drained, loose garden loam is preferred. Most sunflowers are direct-seeded into the garden after the soil has warmed in the spring to at least 60°F. Seeds should be sewn ¼" to ½" deep and the soil kept moist until seedlings emerge. Space seeds about six inches apart and thin to 24 inches (depending on variety) when seedlings become well-established.

Sunflowers are heavy feeders. However, if located in a fertile garden loam high in organic matter, sunflowers grown as ornamentals need little if any additional fertilizer. They can withstand some drought, but perform best when provided with adequate water. Thorough, infrequent watering is preferred to encourage the development of their deep root system.

Remarkably tough and carefree, sunflowers have relatively few insect pests or diseases other than downy mildew, powdery mildew and rust. Timely applications of fungicides can prevent diseases from becoming a problem. If insect pests appear, avoid the temptation to spray insecticides, since the wide array of beneficials attracted to sunflowers will be harmed also.

yellow flowers with orange centers

Suntastic AAS Selection program

When grown for cut flowers, sunflowers should be harvested early in the morning before the plants become heat stressed. Handle cut flowers with care so the petals (ray florets) do not come off. For novel flowers, try immersing the cut stems in vases and add food coloring. After several hours, the flowers will take on interesting new colors or, if yellow coloring is used, original flower color will be intensified.

Their large seeds, rapid rate of growth and carefree nature make sunflowers an ideal choice for children learning to garden. Include a few of the giant types just to give kids a sense of awe and wonderment of the size of plant that can develop from a tiny seed. Even experienced gardeners enjoy the satisfaction that comes from growing what truly is an "all American" flower.

Sunflower Trivia:

  • The world's tallest sunflower measured an amazing 30 feet, 1 inch in height according to the Guinness Book of World Records.
  • The same book lists 889 as the record for people dressed like sunflowers at one gathering.
  • Sunflowers can decrease the growth of neighboring plants due to compounds they contain that are toxic to other plant species. The phenomenon is known as allelopathy.
  • The fear of sunflowers is a mental health disorder known as Helianthophobia.
  • The wild sunflower is the official state flower of Kansas.
  • Sunflower is one of the few plants to have been grown in the International Space Station.
  • At 1.34 billion pounds, North Dakota leads the U.S. in sunflower seed production.
  • In addition to being high in protein, sunflowers seeds are rich in antioxidants which can lower the risk of developing a number of medical conditions.
  • Sunflower butter was developed as a healthier alternative for peanut butter and for those with nut allergies.
  • The world's most valuable sunflowers are on a canvas painted by Vincent van Gogh that sold for over $39 million in 1987 to an anonymous buyer.
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REVISED: May 7, 2021