Sunflowers are recognized worldwide for their beautiful orange, red and yellow flowers. Their seeds and sunflower oil are an important agricultural crop in the U.S. and sunflower meal is used as livestock feed. It can be grown as a green manure cover crop between plantings of small grains or vegetables. Sunflower seeds are valued for their high protein levels.
Sunflower species originated in North America, where evidence shows it was domesticated by Native American tribes as early as 1000 B.C. Tribes carried it south and east where it was observed by European explorers from Canada to Mexico. Sunflowers were introduced to Europe as a curiosity, and they were cultivated for oil by Russian farmers by 1860. Russian cultivation methods increased sunflower oil content from 28 percent to almost 50 percent.
The scientific classification of the sunflower is helianthus annus. It is an annual, erect, broadleaf plant that grows from 12 inches to 108 inches tall. It has a strong taproot and prolific lateral root system. Sunflower plants usually emerge 11 days after planting, and a visible flower head develops in 33 days. Temperatures for productive growth is 64 degrees to 91 degrees Fahrenheit.
Sunflowers are phototropic and follow the sun's rays in their bud stage of development. They face east at the rising sun and turn gradually west as the sun traverses the sky, returning to an eastern orientation at night. This is performed by a flexible portion of the stem just below the bud joint. Mature flowers no longer turn with the sun.
The sunflower head is made of between 1,000 and 2,000 individual flowers joined at a common receptacle. The small flowers grow in an arrangement of interconnecting spirals known mathematically as Fibonacci number sequences. Each subsequent number is the sum of the previous two numbers in this classic mathematical formula.
Sunflowers are minimally drought resistant but have a 6½-foot-long taproot which helps make good use of available water. They grow well in clay to sandy soil with medium to high levels of nutrients from micro organisms.