Helianthus annuus, also known as sunflowers, brighten any size garden with their large daisy-like flowers in shades of yellow, orange, red and bronze. Tall varieties of this easy-care annual are usually used for back-of-the-border plants, cutting gardens and food for wildlife. Shorter varieties make colorful additions to traditional cottage gardens and any container. Sunflowers are an easy plant to start from seed, germinating quickly under the right conditions and growing rapidly.
Choosing the Right Soil for Sunflowers
Sunflower seeds should be sown directly into the soil outdoors or started indoors in peat pots several weeks before transplanting time. For outdoor planting, a location in full sun with well-drained soil is required. If drainage is an issue, 2 to 4 inches of compost can be spread over the soil. Adding 2 cups of complete organic fertilizer, such as a 4-5-4 formulation, per 10-foot row and tilling the amendments into the soil to a depth of 6 inches will provide nutrients during the growing season. Indoors, sunflower seeds are started in 3- to 4-inch pots filled with a well-draining soiless planting media.
Sunflowers and Moisture
Sunflower seeds are planted one to one-half inch deep. Because sunflowers are an oil-rich seed, they require a bit more water for germination. This requires watering the ground thoroughly outdoors after planting and not allowing the soil to dry out completely until germination occurs, and the baby sunflower plant has arrived. Indoors, the soilless media is completely saturated and allowed to drain before 2 or 3 seeds are planted in each pot. Covering the pots with clear plastic wrap slows evaporation, and maintains the proper moisture levels.
The Right Temperature for Sunflowers
Sunflowers germinate best at a soil temperature of 70 to 85 degrees Fahrenheit, but can be planted once the temperature is over 60 degrees. Outdoor planting time is typically several weeks after the last spring frost when the soil has warmed thoroughly. Indoors, a heating mat under the pots can raise the soil temperature to at least 70 F. The seeds will sprout in 7 to 14 days outdoors. Indoors, where the growing environment can be more closely controlled, germination often takes place in six to 10 days.
Sunflowers and Light Requirements
Sunflower seeds do not require light for germination. However, when grown indoors in pots, the plastic wrap is removed at the first sign of germination and the uncovered pots are placed in bright, indirect light. When the plants have their first set of true leaves, the seedlings are thinned to 1 per pot and an all-purpose water-soluble fertilizer is applied at half strength weekly. Outdoors, thinning small varieties to 6 inches apart and large varieties to 3 feet apart allows ample light and airflow around sunflower seedlings.