What Is the Temperature to Grow a Sunflower Seed?

Climate Zones

• Sunflowers are annual plants that don’t overwinter. This means that you may grow them in just about any location, regardless of the winter temperatures. Sunflower plants grown in cooler climates may require an early start indoors to allow adequate time for blossoming in the outdoor landscape during the summer and fall seasons.

Germination

• Sunflower seeds germinate successfully at minimum temperature of 41 degrees Fahrenheit. For germination to occur, the temperature of the soil surrounding the seeds must be at least 45 F. Some germination may occur at colder temperatures near 39 F, but temperatures closer to 46 to 50 F provide the best conditions for satisfactory germination.

Growth

• Sunflowers generally stop growing in the late fall or early winter when temperatures dip below 24 F. In warm climates and protected locations, such as in greenhouses or under grow lights, that don’t experience freezing temperatures, these plants stop growing after completing their annual life cycle. The formation of new seeds on spent blossoms provides the means of producing new sunflower plants. The optimal temperature for continued growth is around 70 to 78 F, although these plants grow adequately in temperatures between 64 and 91 F.

Considerations

• As the name suggests, sunflower plants thrive and flourish in open areas of the landscape that provide an abundance of sunlight. Shady locations and indoor settings may lead to poor growth, regardless of the temperatures. Sunflowers grown in suitable locations with optimal temperatures begin to sprout about 11 days after planting the seeds. They form flower buds within 33 days of sprouting and continue blooming for about 30 days. Hard freezes after germination can damage sunflower plants, often causing individual areas of frost damage among healthy sections of vegetation, although severe freezes may cause the loss of entire plants.