The Culture of a Sunflower

Site Preparation

• Both annual and perennial sunflowers usually grow best with a full six to eight hours of daily sunlight. Although they grow in most soil types, soil with a pH, or acidic-alkaline level, of 6.0 to 6.5 leads to their healthiest growth and flowering. Their garden beds must drain well because overly wet conditions can kill the plants. A 2-inch-thick layer of compost, tilled into the top 6 inches of soil, improves drainage and provides some nutrients for the plants. Annual plants rarely require fertilization. Perennial varieties benefit from the addition of 1 pound of 12-4-6 fertilizer worked into every 50 square feet of soil before planting.

Planting Procedure

• Sunflowers grow readily from seeds, and most annual varieties don't transplant well. Sow the annuals' seeds directly in the garden bed after the danger of frost has past in spring. The annuals that have large seeds require sowing at a 1 inch depth while small seeds require planting at a 1/2 inch depth. In moist soil, the seeds typically sprout within five to 10 days. Perennial varieties are grown from seeds sown in the same manner, or you can use nursery transplants. Plant transplants at the same depth they grew in their nursery containers. Plant spacing varies, with the tall sunflower varieties requiring at least 2 feet between plants and the shorter types only requiring about 1 foot between plants.

Basic Care

• Regular irrigation results in the healthiest growth for sunflower plants. Annual and perennial sunflowers require about 1 inch of water weekly from rain or irrigation, which is enough water to moisten the top 6 inches of soil. A 2-inch layer of mulch helps to retain the moisture in their soil. Perennial sunflowers also require annual fertilization in spring, using the same amount and type of fertilizer applied before planting. Most annual types produce edible seeds. You can harvest a flower's seed head when the back of the flower disk dries and turns yellow after the flower wilts. Cut back perennial sunflowers in fall after they die back naturally, and they should return the next spring.

Pests and Diseases

• Few diseases plague sunflowers, although they may suffer from fungal problems if the plants are overcrowded. Keeping the beds weeded, spacing the plants correctly and avoiding overhead watering prevents most fungal concerns. Insects also rarely bother sunflowers, especially if the plants are healthy and well-tended. Squirrels and birds may raid seeds from annual varieties. Covering developing seed heads with paper bags until you harvest them can save the seeds from animal pests.