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Sunflowers are native to North America, and grow wild in many areas of the U.S. Sunflowers have a long and varied history as an economic plant, but the time and place of its first cultivation is uncertain.
Sunflowers are tolerant of both low and high temperatures, with greater tolerance to low temperatures. Sunflower seeds can germinate at 39°F, though temperatures of at least 46 to 50°F are needed for satisfactory germination. Seeds are not affected by vernalization (cold) during early germination stages. Seedlings in the cotyledon stage can survive temperatures as low as 23°F. Later stages of the plant may suffer damage from freezing temperatures, with temperatures below 28°F required to kill maturing sunflowers. The optimum growth temperature range is 70 to 78°F, though a wider range of 64 to 91°F has little effect on productivity. Extremely high temperatures can reduce oil percentage, seed fill, and germination.
Sunflowers are adaptable to various soil conditions but grow best on well-drained soils with high water-holding capacity and a nearly neutral pH (6.5-7.5). Their performance on high-stress soils, such as those with drought potential, salinity, or wetness, is not exceptional but compares well with other commonly grown commercial crops. Maintaining a moist seedbed is crucial for uniform germination and emergence across the field. Proper soil drainage is essential for successful sunflower production.
Sunflowers can be planted at various times throughout the season. In the northern Great Plains, planting typically occurs from May 1 until late June. For late planting or replanting in northern areas, early maturing hybrids are preferred. Planting can begin as early as two weeks before the last killing frost and as late as 100 days before the first killing frost in the fall.
Sunflower grows well in a variety of plant populations and spacings. With adequate weed control, no yield differences are observed between sunflowers seeded in rows or solid seeded. Fields with row spacings of less than 20 inches are considered solid seeded. A planting depth of 1 to 3.5 inches ensures the seeds reach available moisture and results in satisfactory stands. Planting too deep can reduce stands and yields. For soils prone to crusting or packing, such as silt loam or clay, a shallower planting depth is recommended. Row spacing is typically determined by the available machinery, which may be 30 or 36 inches for corn, soybean, or sorghum growers, or narrower rows for sugarbeet growers. Trials have shown no significant differences in sunflower yield, oil percentage, seed weight, test weight, height, or flowering date between narrow and wide rows across five plant populations. Thus, row spacing can be adjusted to fit available equipment, with 30-inch rows being the most common. Semi-dwarf varieties may perform better in narrower rows at high populations.
The growing season for sunflowers can vary based on summer temperatures, moisture distribution, and soil fertility. Sunflowers reach physiological maturity when the back of the head turns from green to yellow, and the bracts begin to brown, typically 30 to 45 days after blooming, with seed moisture around 35%. While sunflowers mature well before they are dry enough for combining, there are often only a few good days in October when the seed is dry enough for storage. For temporary storage, seeds should be below 12% moisture, and for long-term storage, below 10%. Seeds with up to 15% moisture are acceptable for temporary storage in freezing weather, but spoilage can occur after a few warm days. Harvesting sunflowers at higher moisture content often results in higher yields and less field loss, while early harvesting minimizes exposure to late-season wet and cold weather. Mechanical drying is frequently required to complete the harvest. Commercial sunflower headers help reduce seed loss during direct combining, with metal pans (9 to 36 inches wide) for catching mature seed and a three-armed reel. Narrower pans (9 inches) are ideal for diagonal harvesting, reducing loss in certain situations.
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