Growth Period for Sunflowers

Short Growing Season

• Sunflowers can take as little as three months to mature from seed to harvest under ideal conditions. Commercial growers often plant a crop of sunflowers between planting times for other crops to maximize production in one area. With a 6-foot-deep tap root, the sunflower tolerates hot, dry soil conditions well. Cooler weather and late seed planting lengthens the growth period for sunflowers.

Seed Planting and Germination

• Plant sunflower seeds when the soil warms above 39 F in spring. The best germination rates occur in soil between 46 and 50 F, according to the University of Wisconsin Extension. Plant sunflowers 1 inch deep in a prepared garden bed or field. Till the soil prior to planting to loosen the ground. Sunflower seeds emerge in four to five days in soil above 50 F. Colder soil extends germination time to 11 days. Common planting times for sunflowers fall between April and July. In frost-free climates, plant sunflowers any time of year.

Growth Rate

• Commercial sunflower varieties grow 6 to 7 feet tall. Once the seedlings emerge, growth happens rapidly and the sunflower produces the first visible flower about one month later. The plant continues to gain height after the first flowers form. The plants mature about two months later. Growing times vary slightly depending on the variety. Sunflowers tolerate a temperature range between 64 and 91 F, but prefer temperatures between 70 and 78 F, according to Purdue University.

Harvest

• Wait until the flower heads mature to harvest sunflowers. Wild sunflowers keep their heads up to the sun as the seeds mature. To help prevent birds from stripping crops before harvest, plant breeders have developed varieties that drop their heads towards the ground as they mature. Look at the back of the flower head. As the plant matures for harvest, it turns from green to pale yellow or light brown. Cut the flower head from the plant and shake or rub the seeds loose.