How To Grow Sunflowers
How To Grow Sunflowers
Charles T. Behnke
Sunflower is the common seed name for the genus Helianthus. The sunflower is native to North America, and was used by early North American Indians for food and pressed to make hair oil. Meal from processed seed has been used for livestock feed. Today, whole seeds are used for oil, bird seed and snacks. The seeds are a rich source of calcium plus 11 other minerals. The 50 percent fat composition is mostly polyunsaturated linoleic acid.
As a garden plant, the sunflower is valuable for forming a background screen. A rapid grower, it reaches a height of 8 to 12 feet in rich soil.
This rapid growth could cause competition with other garden plants, especially by shading. Sunflowers can be planted between groups of shrubs, particularly where these form a background. For smaller gardens, the multi-branched species are more suitable. Dwarf forms of 24 inches in height make a spectacular bed by themselves.
When growing sunflowers for bird food or human consumption, select the confectionery types over the oil types.
Sunflowers do best when grown on soils with adequate water-holding capacity, internal drainage and proper fertility. They will tolerate a wide range of soil types; however, one that is too high in nitrogen encourages excessive plant growth that will check maturity of the flower heads. Adequate levels of phosphorus and potassium are recommended, and, as with any garden activity, frequent soil tests are recommended to get good results. The plant’s roots go deep and spread extensively, so the sunflower can withstand some drought and nearby cultivation. Sunflowers should not be water stressed during the critical period; about 20 days before and after flowering.
Plant seed into moistened soil one to two inches deep, but no deeper than three inches. Space seed 12 inches apart in rows spaced 2 to 2 1/2 feet apart. Plants grown for large heads should be spaced farther apart or scattered around the garden.
In Ohio, planting can take place from early to mid-May. Seed bed soil temperature must be between 42 and 50 degrees F with temperatures above 50 degrees F preferable for germination to occur rapidly. Depending on variety and environmental factors, germination will occur in 7 to 12 days. Plants will mature in 80 to 90 days.
For the home situation, seed can be started in four-inch peat pots and transplanted outdoors. Transplants may grow taller and flower sooner than seed started plants. They should start to flower in ten weeks.
Weeds can be a problem for sunflowers. Weed control is practiced for the first four to five weeks after seed emergence. For the home garden, hand weeding and mulching are the best methods.
A common disease of sunflowers is Sclerotina or white mold, which causes stalk and head rots. Disease spores can live for many years in the soil. Other common diseases are downy mildew, rust and verticillium wilt. Sanitation and crop rotation should be considered for control in the home garden.
The sunflower head moth is the major insect pest. The moth attacks at flowering time with the larvae feeding on floral parts and tunneling through developing seed. Aphids and whiteflies also can be a problem.
Birds can be troublesome near harvest time. Seeds are exposed and the large flower head serves as a feeding perch. To deter birds, use frightening devices and human activity in the immediate area before damage is expected. Flower heads can be covered with plastic netting or cheesecloth.
Harvest begins in mid-September and can run into October. A check of the flower head will indicate maturity; florets in the center of the flower disk are shriveled, heads are downturned, and a lemon yellow color is on the backside. Pull a few seeds and split them with a knife to check if seed meat has filled. Poorly filled seeds may be due to a lack of pollinating insects.
To harvest, cut the seed head with about a foot of stem attached and hang in a warm, dry, well-ventilated, rodent and insect-free place. A paper bag with holes or cheesecloth can be placed over the heads to catch falling seeds as they drop during drying. Seed heads can be allowed to ripen on the plant, but cheesecloth or nylon netting will be needed for bird protection. Once the seed is dried, it can be rubbed easily from seed heads. Humidity levels must be kept low to prevent spoilage.
Raw mature seeds may easily be prepared at home by covering unshelled seeds with salted water (2 qts. of water to 1/4 to 1/2 cups salt). Bring to a boil and simmer two hours or soak in a salt solution overnight. Drain and dry on absorbent paper.
Put sunflower seeds in a shallow pan in a 300 degree F oven for 30 to 40 minutes or until golden brown, stirring occasionally. Take out of oven and add one teaspoon of melted butter or margarine to one cup of seeds. Stir to coat. Put on an absorbent towel. Salt to taste.
Common Sunflower (H. annuus) – Includes the cultivars H. bismarkianus‘s, single yellow flower, 6 to 8 feet tall; H. citrinus, primrose yellow flowers, 6 to 8 feet tall; H. giganteus, Russian Giant, large, single yellow flower grown mainly for seeds, 10 to 12 feet tall.
Silverleaf Sunflower (H. argophyllus) – Stems and leaves covered with silky gray down, especially on younger growth. Flowers golden with purplish brown center, plants 5 to 6 feet tall. Silvery leaves used in fresh and dried flower arrangements.
Cucumberleaf Sunflower (H. debilis) -Four-foot plants with multiple branches. Excellent for cutting. Three-inch flowers have a purple disk and yellow rays.
Ohio State University Extension Fact Sheet Horticulture and Crop Science 2021 Coffey Rd., Columbus, Ohio 43210-1086