Sunflower species originated in North America and are known to have been cultivated on the continent since 1,000 B.C. The sunflower enthralls gardeners with its ability to seek out and move its head in tune with the rays of the sun. The plant typically grows to a height that surpasses most humans.
Height -The height of the sunflower plant (Helianthus annuus) varies widely depending on the length of the growing season and planting conditions, but typically the sunflower stretches to a mature height of between 5 and 7 feet. Dwarf varieties often attain a full height of 3 to 4 feet. The growing season is relatively short, requiring 90 to 100 days for the plant to reach full maturity.
Temperature -The premiere height of a sunflower will be achieved when it is grown in temperatures ranging from 70 to 80 degrees Fahrenheit. However, the plant easily tolerates a wider range of temperature from 64 to 91 degrees Fahrenheit, according to the Purdue University Horticulture Department. The seed will germinate at 39 degrees Fahrenheit, with extreme temperatures below 28 degrees Fahrenheit necessary to damage the height potential and health of the sunflower.
Environment -The sunflower is not especially drought-tolerant, so lack of water can affect the plant's ability to achieve an extensive height. Still, the taproot of the sunflower usually stretches more than 6 feet into the ground, a feature that allows it to maintain health when water is in short supply. Three weeks before and after flowering is the most critical time for the sunflower; lack of irrigation during this period will damage its production.
Problems -The sunflower grows well in a variety of soil types, including sand and clay. The earth surrounding the sunflower should be well-drained as it does not tolerate flooding or standing water. Several different forms of fungi may attack the plant and damage how tall it grows, including downy mildew, verticillium wilt, leaf spot, rust, and sclerotinia stalk and head rot. The larvae of the sunflower moth, banded sunflower moth and sunflower bud moth all feed on the head of the sunflower, but typically do little to minimize its full height potential.