It is an annual plant of large proportions, which can reach over 3 meters high. It is a plant with few branches and the stem is thick, erect and massive.
It has deep roots formed by a main taproot and abundant secondary roots.
Its leaves, between 5 and 30cm long and half as wide, are large, oval, discreetly toothed, petiolated, with three main veins and rough to the touch. The upper leaves are alternate and lower ones opposite.
The inflorescence, also known as floral head, is large, 10 to 30cm in diameter and consists of hundreds of tiny tubular flowers.
In the outer section we can find the ligulas or external unfertile flowers in one or two rows that look like petals. These flowers, on display from summer to fall, are golden yellow and have no direct reproductive function, but they serve as attraction for insects, which help the plant in the process of pollination.
The fertilized flowers develop into its receptacle - in provision similar to honeycomb - one of the oleaginous fruits most popular in the world: the "sunflower seeds". they are angular achenes, 8-15 mm long, ovoid, flattened, with pericarp (or outer covering) shiny black, white or striated, depending on variety.
When the plant is fertilized, when ripe, its floral head contains between 250 and 1500 achenes, depending on its size and the number of floral head that the plant has. In plants with only one inflorescence, the seed quantity is larger, while in poly-flowered plants there are less seeds.
The back of the flower head is made up of a series of green bracts, like the stem.
The floral head presents heliotropic movement which is produced by the twisting the stem in a process that is called nutation. At dusk, the stem returns slowly to its upright position.
At the maturity of the sunflower plant, that's to say, when it does not produce more seeds (from 35-40 days after flowering), the back of the flower head is yellow and its bracts become brown.
It flowers from Summer - Autumn.
Although it tolerates drought because of the capacity of its roots to extract water from the soil, - it is a plant that goes on better in irrigated lands than in dry farming- it is important to water abundantly during the bloom to get big flowers and seeds in good state.
For its seeds, for the production of oil, for fodder production, to produce honey and like a garden plant.
It has to be exposed to full sun, being the ideal temperature between the 21-25ºC; and that of sowing between 8 and 10ºC
It must be reproduced from seeds in autumn or at the end of summer.
Sunflower soil requirements
- It prefers loamy and deep soils that preserve the humidity,and a pH between 6 and 8.
- It is convenient to fertilize it before the flowering so that the flowers can become big and produce good seeds.
. A rich mixture in potassium, nitrogen and phosphorous is the most appropriate.
Sunflower deseases and plagues
Sunflower is mainly affected by the mildew, the parasitic weed and the rust, besides the worms and the birds.
Another species of "Helianthus"
Helianthus decapetalus----------------- Girasol de fulla fina.