The sunflower, or Helianthus annuus, is an annual flower that is famous for its extremely large and vividly yellow blooms. These plants are native to North America, but they are widely cultivated all over the world today as ornamentals, food plants and for their valuable oil. Many people enjoy growing the flowers, because they are quite easy to cultivate and are a great way to brighten even a small garden.
Origin and History
It is estimated that the sunflower was domesticated around 1000 BCE in North America, presumably for the purpose of using the oil-rich and highly nutritious seeds. They were also used as a source of purple and black dyes. When European explorers were introduced to the plant, they brought it home with them and cultivation in Europe dates to around the 1600s. By the late 19th century, they were being grown extensively in Russia for their oil, but also in many other parts of Europe. France, in particular, has become famous for its sunflowers, perhaps because of Van Gogh's lush paintings of fields in bloom.
A domesticated sunflower can grow to over six feet (two meters) in height, producing one or many composite blooms, known as heads, on a coarse stem with rough, hairy leaves. The “flower” is actually composed of hundreds of tiny florets packed together; only the outermost ones have long petals. When the head is fertilized, the florets on the inside of the head develop into seeds, while the petals along the sides wither and fall off. In addition to the classic yellow, these petals can be white, orange or maroon in color and the seeds may develop in white, black or striped forms.
The most well known trait of the sunflower is probably its heliotropism. The flowers buds turn to face the sun, but, contrary to common belief, the mature heads do not. The buds face east in the morning and slowly track the sun across the sky. After dark, the heads reorient themselves to face the east again. This tendency is more pronounced in domesticated forms. It is thought that the shaded sides of these fast-growing plants grow more quickly, causing the turning motion through the course of a day.
The plant has a long root system, penetrating down to over six feet (two meters) if conditions are right. This can enable it to exploit sources of water relatively deep in the ground. For this reason, it can often tolerate dry spells, but it is not classed as drought-resistant.
Growing sunflowers is easy in most parts of the world and in some areas the flowers can actually turn into weeds if allowed to grow unchecked. They thrive in USDA zones 3 through 10. The plants will survive frost, but may be damaged and will die if subjected to severe cold. They grow best at 70-78°F (21-25.5°C), but will tolerate a much wider range.
Sunflowers are annual plants that die shortly after setting seed, so they can be grown anywhere where summer temperatures remain above freezing. They are normally propagated by the seeds, which germinate best at 46-50°F (7.7-10°C). Seeds should be planted between 1 and 3.5 inches deep. The plants are fairly unfussy about soil types, but good drainage is advised.
Due to their large size and attractive flower heads, sunflowers are popular ornamental plants. Their rapid growth and ease of cultivation make them a good choice for children who want to do some gardening. Most garden stores carry an assortment of varieties, for people who want to grow them in exotic colors like maroon and white.
The seeds have a high oil content — 39-49% — and are an important source of food products. The oil is among the most popular for cooking purposes and is used in the production of margarine. It is high in unsaturated fats, which are considered healthy, and, aside from cooking, is used in many ready-made snacks such as potato chips, or crisps. It is famously nutty in flavor and is also considered to be very good for the skin.
Since the seeds are rich in protein and several nutrients, they are a popular snack in many regions of the world, especially when roasted. Sunflower seeds are widely used as food for various pets, especially birds and some rodents, such as gerbils. They are also sold as food for wild birds, to be placed in garden bird feeders.