You’ll remember from school that sunflowers follow the sun. You might not remember that the behaviour is called heliotropism. The baby sunflower twists around at night so it faces the first rays of the morning sun, and then it turns its head through the day, following the path of the sun to maximise photosynthesis and power its growth.
That’s not the whole story. Once the plant starts to mature it turns due east and stays there, warming before nearby plants and luring the first of the morning’s pollinators. Something to remember when you plant them: how depressing to have them grow up and turn their backs on you.
Sunflowers at Lambley Nursery in Ascot, Victoria.Credit:Robin Powell
Heliotropism is not the only reason the sunflower is the favourite plant of any junior science teacher. That giant head is not a single flower, but a mass of tiny florets surrounded by an array of petals. A sunflower typically has 1000 to 4000 florets packed into the head, in a spiral that follows the Fibonacci sequence and fits the most florets in the smallest space.
Sunflowers are also phytoremediators: plants that remove toxins from the soil. Their gold medal performance in this discipline was at Chernobyl, where fields of sunflowers took up radioactive metals from the soil and stored them in their tissues. The plants were harvested, then burned to create a radioactive ash that was vitrified and buried in a container.
So why didn’t sunflowers repeat the performance at Fukushima? Were they planted too soon after the incident, was there something about the soil profile there, or the variety planted? Research continues.
Sunflowers turn towards the sun to get what they need.Credit:Robin Powell
In central Victoria, geneticist Keith White has been researching sunflowers. White has spent most of his career breeding new strains of agricultural crops such as canola, but a couple of decades ago started working with sunflowers, primarily for the cut flower industry. His Copsley Ornamentals FleuroSun sunflowers are pollen-free, an important requirement for florists dealing with brides who don’t want the hired linen, or worse, their dresses, stained. As a bonus, pollen-free flowers last much longer in the vase and in the garden.
White’s near-neighbour, plantsman David Glenn, grows a selection of FleuroSun sunflowers in his garden at Lambley Nursery, where they attract enthusiastic human and insect visitors (while they don’t produce pollen, they do produce nectar, so are a food source for insects).
Glenn sows seed every few weeks from October to January to get an extended display of sunflowers in colours ranging from soft lemon to dark burgundy that lasts for months. He grows and sells the varieties that produce sprays of flowers rather than a single flower on a single stem. The plants produce an impressive 40-50 flowers each, and some are suitably sized for growing in a pot, so balcony and courtyard gardeners don’t miss out.
In Sydney, sunflowers of any variety can be planted now for flowers in about 10 weeks. Sunflowers are best sown where they are to grow. Choose a spot with at least six hours of full sun a day. And don’t forget to consider which direction that sun is coming from!
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