Sunflower is an annual herbaceous plant native to North America; widespread in Europe and Australia, cultivated for food use, especially in the oil industry. The oil varieties have imposing dimensions, with stems up to two meters high and flowers with a diameter of 25-50 cm, while the garden varieties are kept within 80-90 cm of height, with dwarf varieties of 30-40 cm in height . This genus of plant has erect, fleshy, rough and rigid stems, which bear large alternate, leathery leaves, with an elongated petiole; in the height of summer, at the apex of the stems, a large flattened inflorescence develops, called calatide, consisting of numerous little flowers, surrounded by one or more turns of golden yellow bracts; in late summer the little flowers give way to the fruits, woody achenes, of gray-cream color, streaked with black. The "walnut" inside the achene is edible. The inflorescence of the sunflower is equipped with heliotropic movement: the flower is always facing the sun, from this property derives the name of the plant. There are numerous cultivars, even of small dimensions within 15-20 cm, with flowers of various colors, from pink to red.
To obtain the best possible growth, sunflowers are planted in full sun; they can also develop in partial shade, as long as they can enjoy exposure to sunlight for at least 5-6 hours a day.
These plants grow best in places with hot summers.
Sunflower garden species like to be watered regularly, leaving the soil to dry very well between one watering and another.
They can endure even long periods of drought without problems; specimens belonging to this variety are more afraid of water stagnation than drought. In fact, they can cause root rot that irreparably compromises plant growth.
This kind of plant does not require special fertilizations.
Sunflower specimens grow without problems in any terrain; to obtain prolonged and abundant blooms it is good to work in depth the soil in which a sunflower is to be placed, adding a good quantity of organic fertilizer or slow release fertilizer. These annual plants develop a radical root system of considerable size, so it is advisable to avoid growing them in pots.
The multiplication to obtain new plants is by seed; they are sown in a warm bed in February-March, to allow correct development at higher temperatures, without the risk of abrupt drops in temperature compromising health, or directly abiding in April-May. The seeds collected from the flowers of the previous year do not always produce plants with characteristics identical to those of the mother plant.
Sunflower: Pests and diseases
Occasionally aphids are placed below and within the inflorescences. In this case it is advisable to intervene promptly through the use of one of the many specific products available on the market, or, using natural methods based on nettle or garlic, with which compounds are prepared to be sprayed on the affected plants.