One of the most important crops in agriculture today is the common sunflower (Helianthus annuus). The plants are characterised by coarse, hairy stems and leaves as well as large circular heads composed of small yellow flowers in the centre that develop into seeds, with a layer of sunshine-yellow petals around the outside that attract pollinators such as bees and butterflies. Sunflowers are an easy crop to grow and deliver a burst of colour in the garden. They can be sown any time from early spring to midsummer.
They love the heat and will need 6 – 8 hours of direct sunlight to do well.
Sunflowers are not too particular when it comes to soil, but those tap roots need space to grow and they can’t appreciate waterlogged soil. Dig the soil over to at least 60cm down, and add plenty of compost. Planting in raised beds will also benefit the roots.
Press the seeds about 2cm deep into moistened soil, about 30cm apart. Flood the row of seeds with water and keep the soil moist until they have germinated. Sunflowers will need to be protected in windy areas as the seed heads can be damaged. A wall or fence works well for shelter and support.
The tall varieties can be planted at the back of a bed or against a wall or fence, but there are also dwarf or pot varieties that grow to a more versatile height of 40 – 60cm. Besides the traditional golden yellow with black centre, there are also shades of red, light lemon-yellow, tangerine and bronze-red. You should find many varieties in seed form at your local nursery or garden centre.
Beating the birds to the harvest may be tricky, but do try because sunflower seeds are a good source of vitamin E and selenium, which are both good antioxidants. The seeds are usually ready to harvest about 30 – 45 days after the flower opens, but that depends on the weather. When the seed head begins to turn brown, test a few seeds by taste. If they are ready, cut the flower head off, leaving a bit of stem attached, and hang it upside down indoors in a cool dry place with good airflow until the seed heads are dry. The seeds can be pried out with a fork.
For the vase
Sunflowers are excellent cut flowers. When preparing the flowers for the vase, first remove all leaves that will be below the water line. Then, while holding the stems under water, cut the ends of each stem at an angle to enable them to absorb the maximum amount of water. They will last longer if plunged right up to their blooms in a bucket of deep water and left in a cool place overnight before arranging.
Why do sunflowers follow the sun
Sunflowers are well known for their heliotropic movement, following the sun during the day and even repositioning themselves during the night to start in the morning facing east. What is interesting is that scientists don’t really know why they do this. Recent studies say there is growing evidence that they have an internal clock, a circadian rhythm, which is a biological process that recurs naturally over a 24- hour cycle and has nothing to do with light or sunlight. What has also been noticed is that younger plants tend to solar track while older more mature plants will point in a fixed direction east. Fruiting heads then turn downwards.
It may just be that Mother Nature has given the sunflower an advantage in that mature plants face east to heat up quicker, thus attracting five times as many pollinators than west-facing blooms. Other studies confirm that bees and other pollinators prefer warm flowers, and the sunflowers oblige.
It is possible that on a cloudy day, when solar energy is absent, sunflowers will face each other to harness mutual energy. Whatever the reason, they are fascinating plants and their habits continue to be something of a mystery