Learn About Sunflowers
How to Sow
Sunflowers are grown from seed sown directly in the garden after frost.
- Direct sow seeds in average soil in full sun after all danger of frost.
- When choosing a site consider that sunflowers need a well-drained soil. They face the sun, so make sure they are in an open area of the garden. The taller varieties will cast shadows on other plants, so plant these at the north end of your garden.
- Prepare the soil by removing weeds and working organic matter into the top 6-8 inches of soil; then level and smooth.
- Most plants respond well to soils amended with organic matter. Compost is a wonderful form of organic matter with a good balance of nutrients and an ideal pH level, it can be added to your planting area at any time. If compost is not available, top dress the soil after planting with 1-2 inches of organic mulch, which will begin to breakdown into compost. After the growing season, a soil test will indicate what soil amendments are needed for the following season.
- Sow seeds ½ inch deep in groups of 2 or 3 seeds. Space the groups 18-24 inches apart, depending on the variety.
- Firm soil lightly, water and keep evenly moist.
- Seedlings will emerge in 7-10 days.
- Thin to one plant per group when seedlings have two sets of leaves.
How to Grow
- Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, so control them by either cultivating often or use a mulch to prevent their seeds from germinating.
- Mulches also help retain soil moisture and maintain even soil temperatures. For annuals an organic mulch of shredded leaves lends a natural look to the bed and will improve the soil as it breaks down in time. Always keep mulches off a plant’s stems to prevent possible rot.
- Keep soil evenly moist but not wet.
- Once established sunflowers can tolerate drought.
- No fertilizer is needed unless the soil is poor. Do not over fertilize.
- Monitor for pests and diseases. Check with your local Cooperative Extension Service for pest controls recommended for your area.
- Some varieties only produce one bloom so once the bloom is spent, the plant may be removed.
- Remove plants after they are killed by frost in fall to avoid disease issues the following year.
- Edible sunflowers will mature in about 3 months or more after sowing. To harvest the seeds, cut the heads off after the stalks are quite dry but before fall or winter rains come. Check the flower heads for maturity to see if the florets in the center of the flower disk have shriveled and the back of the flower head is turning yellow, or the head is starting to droop. Cut flower-heads with a foot of the stalk attached. Hang heads in a warm, dry, well-ventilated place so the seeds may fully ripen and dry. Cheesecloth, netting or a paper bag with holes punched in for ventilation should be placed over the head to protect the seeds and to collect those that may drop from drying.
- Shorter varieties may be grown in containers. Be sure to use a commercial potting mix.
- Pollenless varieties make terrific cut flowers.
Common Pests and Problems
Common Disease Problems
Alternaria Leaf Spot: Small, round reddish brown spots with white to gray centers form on the upper surface of the leaves. The lesions may encircle the stems and cause wilt. This disease is worse in warm, wet or very humid weather. Burpee Recommends: Avoid getting water on the foliage. Remove infected plant parts and do not work around wet plants. Provide plenty of air circulation. Contact your Cooperative Extension Service for fungicide recommendations.
Downy Mildew: This fungus causes whitish gray patches on the undersides and eventually both sides of the leaves. Burpee Recommends: Rotate crops with plants in a different family. Avoid overhead watering. Provide adequate air circulation, do not overcrowd plants. Do not work around plants when they are wet.
Powdery Mildew: This fungus disease occurs on the top of the leaves in humid weather conditions. The leaves appear to have a whitish or greyish surface and may curl. Burpee Recommends: Avoid powdery mildew by providing good air circulation for the plants by good spacing and pruning. Contact your Cooperative Extension Service for fungicide recommendations.
Rust: A number of fungus diseases that cause rust colored spots on foliage and stalks. Burpee Recommends: Practice crop rotation. Remove infected plants. Contact your Cooperative Extension Service for fungicide recommendations.
Septoria Leaf Spot: It is most severe during rainy seasons in closely planted gardens. Water soaked circular or angular spots with a greasy, greenish appearance on lower leaves appear. Fungal spores are produced and darken the center of the spots. There is a progressive loss of foliage. Burpee Recommends: Remove and destroy infected plant debris. Don't handle or brush against plants when they are wet. Rotate plantings. Remove weeds growing nearby.
Common Pest and Cultural Problems
Aphids: Greenish, red, black or peach colored sucking insects can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps who feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.
Cutworms: These insects cut off the seedlings at the soil level. Burpee Recommends: Place a paper cup collar (use a coffee cup with the bottom cut out) around the base of the plant. They are usually mostly a problem with young seedlings. You can also control by handpicking and controlling weeds, where they lay their eggs.
Flea Beetles: These small hopping beetles feed on plant foliage and may spread diseases. Burpee Recommends: Rotate crops with plants in a different plant family. Use floating row covers to prevent damage to young foliage.
Sunflower Moth: A small gray sunflower moth sometimes lays its eggs in developing sunflower blossoms. Its larvae are greenish-yellow with 5 brown stripes down their backs. They feed in the flower and destroy seeds, creating a mass of webbing and debris. Burpee Recommends: Hand pick the worms from the plants and drop them into a plastic bag for the trash. Consult your Cooperative Extension Service for other insecticide recommendations.
Sunflower Stem Weevil: Adults are dark brown with light spot about 1/8 inch long. Larvae are pale. They bore into the stems and the foliage turns yellow and wilts. Plants fall over and die. Burpee Recommends: Delay planting so beetles will emerge and die before laying eggs. Remove and dispose of debris at the end of the season.
What direction do the flowers face? Sunflowers follow the sun.
Are any of the seeds toxic? No, they are not toxic, however only the giant sunflower seeds are good for eating.
Why are the seeds hollow? This could be from a lack of pollination, sunflowers need insects for pollination. Also sunflower moth larvae may leave tiny holes in the shell.
How many flowers does each stem of the giant flowers get? One.
How long do sunflowers bloom? Sunflowers bloom for about 4-6 weeks.