What better way to celebrate the start of Summer than with a feature post on the wonderful exuberant Sunflower, Helianthus annuus! Sunflowers belong to the daisy family, Asteraceae, and the genus Helianthus has over 70 species, most of them native to North America, except for three species from South America. Most are ornamental, frost-hardy herbaceous perennials, like the Jerusalem Artichoke, Helianthus tuberosus, but the Common Sunflower, familiar to most people, is an annual, as indicated by its species name: ‘annuus’. The genus name Helianthus is derived from two Greek words: ‘helios’ meaning ‘sun’ and ‘anthos’ meaning ‘flower’.Mythology
In Greece, the sunflower is a symbol of the water nymph Clytie, who was turned into a sunflower after she lost her love Apollo, and constantly faces the sun, awaiting the return of his chariot. The visual similarity of the flower to the sun makes it a symbol of worship and faithfulness in many religions. In fact, the Incas used South American sunflowers to worship the sun in their temples, where priestesses wore necklaces of sunflowers, cast in gold, as well as sunflower crowns. The Hopi Indians of North America also used sunflowers in their tribal rituals, as well as for food and a purple dye. In China, the sunflower is an auspicious symbol, denoting long life and good luck, its bright yellow colour symbolising vitality, intelligence and happiness. Vincent Van Gogh is famous for his series of paintings, depicting sunflowers in vases, one of which sold for $39 Million in 1987. Here is my daughter’s sunflower painting- just as special and always makes me feel happy.Habitat and Distribution
Native to North America, the sunflower was first domesticated in South-Western USA over 5000 years ago and soon became widespread throughout the Americas. Spanish conquistador, Francisco Pizzaro, saw large crops in 16th century Peru and the sunflower was carried back to Spain, where it was cultivated and hybridized. By the 19th century, it was being cultivated on a wide scale in Russia, the Ukraine and the Caucasus regions for the manufacture of vegetable oil. The sunflower is the State flower of Kansas and the National flower of Russia. Mostly grown in temperate areas, it is now also grown as a commercial crop in the United States, Argentina, India, China, Turkey, the European Union (mainly France and Spain) and South Africa. In Queensland, it is widely grown in the Central Highlands and on the Darling Downs, as seen in the photo below.Description
Helianthus annuus is an annual forb, which grows up to 5 metres tall, with a well-developed tap root, which extends up to 3 metres into the soil. There are now a number of cultivars, varying in colour (yellow, orange, rust red) and height, from dwarf varieties less than 1 metre tall to taller cultivars over 3.5 metres tall. The tallest sunflower ever recorded was 7.76 metres tall, though there is a German record of 8.23 metres tall! There is also a discrepancy in growth rates: one source states 30 centimetres in one day, while another estimate is 2 metres in 6 months- that’s 182 days. For mathematicians, that’s 2000 centimetres in 182 days or 11 centimetres a day! Suffice to say that they are one of the fastest growing plants in the world! Our Burgundy Spray sunflower reached 2 metres last year and was harvested and ploughed in at 20 weeks- that’s 5 months- but we did use plenty of manure! The erect stem is rough and hairy and is branched in many wild varieties, but unbranched in cultivated varieties. The petiolate leaves are dentate (toothed margins) and sticky. The lower leaves are opposite and ovate or heart-shaped, while the leaves higher up the stem are arranged spirally.
Blooming in Summer, the inflorescence is a terminal head (capitulum), 10 to 50 centimetres in diameter, with a world record of 87.63 centimetres. Each flower head is surrounded by three rows of bracts (phyllaries)- see photo above- and is composed of sterile outer yellow (or orange/ rust red) ray florets, which attract pollinators, and fertile inner brownish disc florets. A single flower head may have up to two thousand disc florets, each with the potential to develop into a seed. If there are multiple flower heads on the same plant, the number of disc florets per head will be much lower. The disc florets open in sequence, beginning at the periphery of the disc and moving inward. The disc florets are arranged in spiral whorls from the centre of the flowerhead, according to the famous Fibonacci sequence, which allows for the uniform packing of the maximum number of seeds on a seed head without any central overcrowding or bare patches at the outside edges. The Fibonacci sequence is a number set, in which each number is the sum of the previous two numbers: ie 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610 and so on, and was described by Fibonacci (also known as Leonardo of Pisa) in his book : Liber Abaci in 1202.
In the case of sunflowers, count the clockwise and counterclockwise spirals that reach the outer edge, and you’ll usually find a pair of numbers from the sequence: 34 and 55, or 55 and 89, or—with very large sunflowers—89 and 144. Another interesting mathematical fact is that each floret is oriented to the next by the Golden Angle, 137.5 degrees. Botanists have not yet been able to determine a mechanistic model that fully explains how the sunflower seed patterns arise, as some plants don’t always show perfect Fibonacci numbers. A study published by the Royal Society Open Science on 18 May 2016 of 657 sunflower photos revealed one in five flowers had either a non-Fibonacci spiralling pattern or more complicated patterns, including near-Fibonacci sequences and other mathematical patterns that compete and clash across the flower head. See: http://rsos.royalsocietypublishing.org/content/3/5/160091 . Another interesting link is: https://plus.maths.org/content/sunflowers. Click on the first article in the search results: ‘Citizen scientists count sunflower spirals’ by Marianne Freiberger.
For more information about sunflowers and the Fibonnaci sequence, see :
and https://www.mathsisfun.com/numbers/nature-golden-ratio-fibonacci.html.Another fascinating fact about sunflowers is their heliotropism (sun tracking) when young. During growth, sunflower leaves and flowers tilt to face the sun during the day, accounting for their French and Portuguese names: Tournesol (French) and Girassol (Portuguese). As the buds open, the flexible part of the stem tissue (the pulvinus) hardens and heliotropism ceases, the sunflower blooms permanently facing east, thereby acting as a living compass! Sunflowers are pollinated by bees, though some modern varieties are fully self-fertile. The following website has some interesting information about sunflower pollination, which highlights the importance of bees. See: http://www.pollinator.ca/bestpractices/sunflowers.html. Initially, each floret is male, the pollen-bearing anthers extending above the rim of the floret, then later on, the style emerges and the stigmatic lobes spread, opening the receptive surfaces for pollination – see the photo below. If there is enough pollinator activity, the pollen is removed from each floret before the stigma opens, reducing the chances for self-pollination. The resultant seeds are 15 to 25 mm long and vary in colour from white to brown and black and even striped.Growing Conditions and Propagation
Heat and drought-tolerant, sunflowers are very easy to grow in most climates, so long as they have full sun all day (6 to 8 hours) and well-dug, nutrient-rich, well-drained soil. They are propagated by seed. Dig the seed bed well with plenty of manure/ compost, as they are heavy feeders, then rake the soil level. Broadcast the seed and rake into the surface or plant seeds individually to a depth of 2 cm. In cool temperate climates, sow seed in Spring after the last frost (we sowed our Burgundy Spray sunflower seeds on 7 October last year); in warm temperate climates, from late Winter to late Spring; and in frost-free subtropical and tropical regions, seed can be sown all year round, though Autumn to Spring is best. Sunflowers prefer long, hot Summers and hot wet humid Summers increase the risk of fungal diseases like downy or powdery mildew or rust. Mulch the seedbed with chopped sugar cane or lucerne to retain moisture, keep the soil cool and deter pigeons or mice. As the seedlings develop, thin them according to the size of the plants. Giant Russian sunflowers grow to over 4m high with a flowerhead of 5o cm, so require 1.5 m between each plant. Water or foliar feed weekly with seaweed extract in the morning, so that the foliage is dry by sunset, also reducing the risk of fungal mould and rot. For show flowers and maximum seed production, apply two handfuls of poultry manure per square metre when the seedlings are 15 cm high and a 4 cm layer of well-rotted cow manure and compost when they reach 0.5 m in height. Stake the stems when necessary- old pantihose are good. The dwarf varieties should flower within 10 to 12 weeks of sowing, while the taller varieties take 12 to 16 weeks to bloom. Our Burgundy Spray sunflower had its first bloom open at 12 weeks, just in time to celebrate the New Year! We harvested the seeds on the 23 February 2016.
If your plants are affected by fungal disease, a general fungicide can be applied. Slugs and snails love browsing on the stems and leaves of sunflowers, so spray the seedlings with an organic snail bait or a mixture of 1 part espresso coffee to 3 parts of water, then mulch, repeating after heavy rain or irrigation. Bees and butterflies love the flowers, while birds, rodents, squirrels and deer are attracted to the sunflower seed, though large amounts are fatal to the latter! There are numerous insect pests, most of which attack other plants as well. More information on these insects and their management can be found on :http://ipmguidelinesforgrains.com.au/wp-content/uploads/Sunflower_IPM-Workshops_north-March2013.pdf and https://www.ag.ndsu.edu/pubs/plantsci/pests/e1457.pdf Seed heads should be harvested when very dry ie once the back of the flower heads are turning yellow or brown. Tie paper bags over their heads, then cut the stems and hang upside-down in a dry, well-ventilated place till fully dry. The seed head can be sharply struck or rubbed across an old washboard to release the seeds. To process sunflower seed for consumption, soak them overnight in a bucket of 1 gallon (4.5 litres) water and 1 cup salt. Redry in a 250 degree Fahrenheit (120 degrees Celsius) oven for 4 to 5 hours and store in airtight containers.For replanting, the seeds are viable for 5 years, according to: http://tcpermaculture.com/site/2013/06/14/how-long-will-seeds-last-stay-viable/, but if you want to check their viability before planting, see: http://homeguides.sfgate.com/check-sunflower-seeds-viable-68389.html.
Sunflowers are grown extensively throughout the world for human and animal food and sunflower oil production. There are two types grown. The first is oilseed, a very small black seed with a very high oil content , which is processed into sunflower oil and meal and is also the seed of choice of most bird feeders. The second type is non-oilseed (confectionery sunflower), a larger black and white striped seed used in a variety of food products from snacks to bread. Sunflower seeds are rich in healthy fats, oil, vitamin E, protein, fibre and minerals and can be eaten raw or roasted for a savory snack or ground into a seed paste (Sun Butter) like peanut butter. They are excellent for promoting heart health and lowering cholesterol. The seeds can also be ground into a sunflower meal and used as a substitute for wheat flour in breads and cakes and the seed husks can be ground into a coffee-like beverage. Sunflowers are also widely used as an animal food, mainly for birds (seeds) and cattle (forage crop or a high protein meal, which is a by-product of sunflower oil extraction and is often blended with soya bean meal). The seeds can also be pressed to make an oil, which has been used in salads and for cooking, margarine production and in industry : as drying oils for paints and varnishes and in beauty products like soap and cosmetics. However, readers should be aware that there is some research about health risks associated with cooking with vegetable oils. See these links for further information: http://www.telegraph.co.uk/news/health/news/11981884/Cooking-with-vegetable-oils-releases-toxic-cancer-causing-chemicals-say-experts.html and https://www.ncbi.nlm.nih.gov/pubmed/20886885. The cooking oil is recycled as a biofuel. For more on the commercial industry overview of sunflowers in the United States, see: http://www.sunflowernsa.com and http://www.soyatech.com/sunflower_facts.htm. Sunflower oil can also be used in medicine: for constipation and lowering bad LDL cholesterol or applied directly to the skin for poorly healing wounds, skin injuries, psoriasis and arthritis and as a massage oil.Native Americans also grew sunflowers for food and oil, medicine, fibre and dyes , as well as to provide shelter for crops of maize, pumpkins and beans. The juice from the stems was used to treat wounds and an infusion of the plant in water was used to treat kidney and chest pain. The fibre from the stalks could be made into cloth and both the seeds and flower heads yielded a dye: purple, blue and black from the seeds and a bright yellow from the flowers.Sunflowers can also be grown as a green manure crop, the plants being dug into the ground once the seedlings reach a height of 30 cm. The plants can bioaccumulate heavy metals in contaminated soil, like lead, arsenic and uranium, and were used to remove nuclear fallout after the Chernobyl and Fukushima disasters.And finally, sunflowers are commonly used in floristry and are often given on the third wedding anniversary as a sign of adoration, strength and loyalty. Stems should be cut early in the morning before the flowerbuds are fully open- preferably ½ to ¾ open. If buying them, the leaves should be a strong green colour and the stems should be strong. They must be sold with a water source, as they shock easily. Remove any foliage below water level and cut the stems on a sharp diagonal (2 to 4 cm from the stem ends), under water if possible to avoid air blockages in the stems. Do NOT bash the stems. Use a preservative to maintain open flowers and change the vase water daily. The flowers have a vase life of 7 to 10 days. The leaves will wilt and die before the flowers, so only retain the upper leaves. To help prevent leaf drooping, add 10 drops of household detergent to 5 litres of water and leave in this solution for 1 to 3 hours, but no longer than overnight. If the leaves do start to droop, immediately recut the stems up to 6 cm and place in deep water with preservative for up to 3 hours. If the flowers droop completely, recut the stems and place them in boiling water to clear the blockage quickly (though the lifespan of the flower will be halved).
I really enjoyed researching my last feature post for this year. The sunflower is a fascinating plant and I hope you enjoyed the post as much as I enjoyed writing it. If I have whetted your appetite to know more, it would be worth trying to source ‘Sunflowers: the Secret History’ by Joe Pappalardo. See: http://www.overlookpress.com/sunflowers-the-secret-history.html.