Care of Helianthus Annuus

Giant sunflower varieties tower at 12 feet tall.

Commonly known as the sunflower, Helianthus annuus is a North American native grown for its decorative flower head, edible seeds and their resulting oil. The annual blooms throughout the summer months.

Planting Location

Sunflowers require a full sun location that receives at least 6 hours of sunlight each day. Plants grown in inadequate light become weak-stemmed and prone to collapse, according to Colorado State University Extension.

Soil Requirements

Sunflowers thrive in most well-draining soils. They grow best in fertile conditions. Dig in a 2- to 4-inch layer of compost or rotted manure prior to planting. After planting, suppress weeds with a 3-inch layer of mulch, such as grass clippings.

Watering

Sunflowers need regular watering, especially when young and just before flowering. Irrigate twice a week during dry weather. Avoid wetting leaves to prevent the development of foliar diseases.

Fertilizing

Sunflowers generally don't require fertilizer, which creates weak stems and inhibits flower production, according to Washington State University Clark County Extension. Apply bat guano or a 5-10-10 fertilizer to nutrient-deficient soil once when the sunflower is 1 to 3 feet tall.

Provide Support

Prevent large sunflower heads from breaking off or plants from uprooting by tying the stem to a 6- to 8-foot wooden stake with garden twine.

References

• Washington State University Clark County Extension: Sunflowers
• Colorado State University Extension: Sunny Sunflowers

Resources

• University of Minnesota Extension: Drying Sunflower, Pumpkin and Popcorn Seeds