A sunflower says “summer” like no other plant. Sunflowers come in many different colours such as yellow, red, orange and maroon, but they are commonly bright yellow with brown centers that ripen into heavy heads filled with seeds.
Sunflowers are members of the Asteraceae family. A sunflower forms a composite head (capitulum) made of masses of simple flowers (florets) that each produce a seed if successfully pollinated.
Each sunflower can develop as many as 1,000 to 2,000 seeds in the middle section of the flower, called the ovary. Sunflower seeds are used to grow the flowers, as well as be used as nutritious food for birds and humans. Sunflower seeds can be harvested and roasted as a healthy snack.
Sunflowers make excellent cut flowers and attract many bees and birds. They are also heliotropic, meaning the flower buds and young blossoms will face east at sunrise and follow the sun during the day. At sunset, the bloom will be facing west. As the flower grows, the head of the plant becomes heavier, and the blossom will generally stay facing east.
Timing: Sunflowers need warmth to germinate so direct sow after the last frost date, from mid-April to mid-May. Seeds can be direct sown as late a June but will produce flowers much later in the season.
Starting indoors is possible but does not gain much time.
Sowing: Choose a site in full sun, with average fertility and good drainage.
Sow 5mm-1cm (¼-½”) deep, and sow about twice as many seeds as you need. Thin this to 30cm (12”) apart for small to medium sized plants, and 60cm (24”) for the tall varieties.
Starting sunflowers is possible but does not gain much time. For growing in containers, choose small varieties. The larger sunflowers have deep roots to anchor them in place and require being directly sown in the garden bed.
Optimal soil temperature for germination: 21-30°C (70-85°F). Seeds should sprout in 10-14 days.
Growing: Enrich the soil 2 cups of all-purpose fertilizer per 3m (10′) of row, and irrigate regularly.
When the plants are 30cm (12) tall, dissolve 5ml (1 tsp) Borax in 350ml (1½ cups) of water and spread over 5m (15’) of row.
This supplies plants with boron, which is essential for producing big, vigorous plants and flowers. Be sure not to over-apply this solution though, as too much boron can harm the plants and do not apply boron to other garden plants.
Sunflowers are not very sensitive to soil pH and can be grown anywhere in the range from 5.7 to just over 8.0.
Harvesting: At the end of summer and into autumn, depending on when the seeds were planted, the sunflower seeds should be ready to harvest.
Allow seed heads to dry on their stems. When the back of the flower head turns yellow, it is ready to be cut from the plant.
Cut off the heads and bring indoors to completely dry out. Then, seeds can be removed by rubbing and pushing against them.
Protection: To keep squirrels and birds away, it may be necessary to put a brown bag over the flowerhead and secure it at the bottom.
Pests and Disease: Few inspect pests cause problems but beware of damage at the lower stems from rodents. Spray the stems of all sunflowers with a solution of water, cayenne pepper and a couple drops of dish soap.
Companion Planting: Sunflowers planted near rows of corn are said to increase yields. Planting sunflowers amid squash plantings can improve pollination and overall production.
Storage: To prepare seeds for eating, use the grey or white-seeded variety. Once the seeds have been rubbed off the big flower head, soak overnight in 4L of water with 250ml (1 cup) of salt.
Drain, then dry in an oven at 250 F for 4-5 hours then store in an airtight container.
The black seeded types are mainly used for pressing oil or birdseed.