Sunflowers are a very large group consisting of both annulas and perennials. 150 species. The most popular sunflower for gardens is the annual, Helianthus annus, but there are many good perennial sunflowers suitable for the garden. In general sunflowers like hot weather, full sun, fertile, moist, well-drained soil but tolerate less. When planting sunflowers beware of the fact that the roots of the plants emit a substance that may inhibit the growth of other plants around them. Because they are often tall plants, sunflowers also tend to shade other nearby plants. When sighting plants take into consideration that the flowers will face the sun. Since sunflowers are cross-pollinated by insects, grow only one variety at a time if seed collection is the goal, or separate varieties by at least 1000 feet. Hybrids and cultivars will not breed true.
Sunflower seeds grow very quickly but seedlings resent transplanting so seed is best planted directly in the garden. Outdoor sowing can be done after the last frost and the soil is warm. Indoor sowing can be done three to four weeks before planting out is anticipated.
Directions for Outdoor Sowing
1. Sow seed ¼” spacing about six inches apart. Seeds germinate in 10 to 14 days with temperatures of 70 to 85 F.
2. Keep seedlings moist but not wet.
3. Thin to 12” apart for dwarf and medium species, 24-36” for tall species.
4. If seed collection is important protect the flowerheads from birds with netting or cheesecloth.
Directions for Indoor Sowing
1. Plant two to three seeds in peat pots to minimize root damage when moving to the outdoors.
2. Keep moist but not wet and place in an area that is 70-85 F. Seeds germinate in 10-14 days under optimal temperatures.
3. Harden off and transplant the whole pot to the garden when the soil is warm, spacing dwarf species 12” apart and tall species 24-36” apart.
4. Cut or pinch out the weaker plants in each pot as you plant.
5. If seed collection is important protect the flowerheads from birds with netting or cheesecloth.