Sunflower (Helianthus annuus) is a food crop of worldwide importance, as well as a good cutflower and a plant that's fun to grow in the vegetable or flower garden. The large flowers turn to face the sun when the plant is young; once the stem becomes woody, the flowers stop turning. Sunflowers are native to North America, and were cultivated for food by native peoples for thousands of years before the arrival of European settlers. The seeds of sunflower are also a preferred food of birds and small mammals, so many people grow them to feed wildlife over the winter.
A sunflower is actually hundreds of tiny flowers clustered together. The disk flowers form the center. These flowers have both male and female components. After pollination, they produce seeds. The "petals" around the disk are ray flowers. They have no reproductive parts and will not form seeds.
Plant sunflower seeds in late spring, after the ground has warmed. Cover smaller seeds with one-half inch of soil; larger seeds with one inch of soil. They should germinate in five to ten days. Thin the seedlings so giant varieties stand two to three feet apart, smaller varieties about one foot apart. Closer spacings could be used to form a tall hedge of sunflowers, but the flowers would be smaller.
Caring for sunflowers is easy. Full sun is necessary for best growth and bloom, and plants should receive an inch of water per week, either from rain or irrigation. There are few diseases or insect pests of sunflowers.
If you're growing sunflowers for cutflowers, bring a container of water out to the garden when you collect them. Cut them with a sharp knife or pair of shears, strip off the foliage, and stand them in the water immediately.
Most sunflowers produce abundant pollen, which will cover the surface on which a vase of sunflowers sits. Some pollenless varieties have been developed for cutting, including 'Moonbright', 'Sunbright', 'Sunbeam', and 'Sunrich'.
Other varieties favored for cutting, in spite of their production of pollen, include 'Velvet Queen' (dark red), 'Valentine' (lemon yellow), 'Autumn Beauty Mix' (yellow to bronze and red, some bi-colors), and 'Italian White' (ivory with brown centers). These varieties will form numerous blooms on branched stems. Double-flowered forms are good for bouquets. Instead of a dark smooth disk, these varieties have fluffy yellow disk flowers in their centers. Although these disk flowers look like ray flowers, they do produce pollen and seeds. Double-flowered varieties include 'Lion's Mane', 'Teddy Bear', and 'Tohoku Yae'.
Plant breeders have developed some dwarf sunflowers suitable for growing in containers or as bedding plants. These new sunflowers are bushy, with three to five inch diameter blooms on plants only one to three feet tall. Dwarf varieties include 'Pacino', 'Big Smile', and 'Music Box Mix'.
If you're growing sunflowers to harvest the seed heads, whether for human or animal consumption, don't cut the heads until the green disk at the back of the flower has begun to turn yellow. At this point the seeds will mature properly if left on the head and kept in a dry, well-ventilated place.
Birds will eat the maturing seed if the heads are not protected. After the ray flowers have fallen off, cover the head with a cheesecloth or paper bag to keep birds away until you cut it and bring it inside. Two varieties popular for seed production are 'Giant Grey Stripe' and 'Mammoth Russian'. Each of these will form a single, very large flower head atop a stem that may reach ten feet or more.
Seeds are ready to store or eat when the disk at the back of the flower has turned dark brown. You can easily remove the seeds by rubbing two heads together, or just rubbing your palm over the seeds. Store raw seeds in a cloth bag in a place with good air circulation. Airtight containers such as jars or tins encourage mold development.
Many people eat sunflower seeds raw, others prefer them roasted. To roast sunflower seeds, spread them in a single layer on a baking sheet, and toast them in a 350° oven for about 10 minutes. When the seeds start to swell and the hulls crack, they're ready. Cool and salt to taste.
Many gardeners put the entire seed head outside to feed the birds, rather than removing the seeds and using a bird feeder. In either case, do not be concerned that the hulls contain a chemical that kills other plants. They don't. Instead, it's the inches-thick build-up of hulls that kills plants near bird feeders. Any other substance applied thickly to a lawn or garden bed would have the same effect. Rake the hulls out of the grass early in spring, and pull any weeds germinating from the spilled birdseed. Alternatively, place the bird feeder where it won't matter that no grass is growing underneath.
The perennial Maximillian sunflower (Helianthus maximillianii), grows six to eight feet tall and bears three-inch yellow blooms in late summer and early fall. It is hardy as far north as USDA zone 3. Jerusalem artichoke (Helianthus tuberosus), another cold-hardy perennial species, is usually grown for its edible root, rather than its flowers. This species is invasive and very difficult to eliminate from the garden once plants are established. Mexican sunflower (Tithonia species) is a tall, branching annual with deep orange sunflower-like flowers that attract butterflies.