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.
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.