Um guia de cultivo passo a passo, da sementeira à colheita.
pH ideal 6.0 to 7.5Temperatura ideal 18 to 28 °CCompasso 30 to 45 cm in the row, 40 cm between rows
Sementeira
Sow direct two or three centimetres deep, with the soil above 12 °C, and thin to thirty or forty five centimetres. Germination takes seven to ten days. It dislikes transplanting because of its taproot. Protect the sowing from birds and rodents with netting, because the seed is a tempting target and vanishes within hours. This variety reaches 200 centimetres or more in height, so choose a sheltered spot and put the stake in at planting time: fitting a support to a grown plant breaks roots and branches.
Solo
It adapts to almost any soil as long as it is deep and free draining, at a pH between 6.0 and 7.5. The root goes down a long way, which is why it stands drought well. It does not need rich soil, but the giant varieties appreciate compost in the planting hole.
Clima
It wants full sun and heat, between 18 °C and 28 °C. It resists drought and strong heat, which makes it an easy crop inland in Iberia. The main problem is wind: tall plants go over easily, so plant somewhere sheltered or stake the giant varieties. On the Portuguese coast the crop starts slowly because nights stay cool and morning fog keeps the leaves wet for hours, so pick the sunniest spot you have, shelter it from wind and space the plants generously so air moves through. Inland in Portugal and Spain heat rather than cold is the limiting factor: in weeks above 35 °C the plant stalls and light shade over midday pays for itself. In France outdoor growing is reliable from the centre southwards, while in northern France and in Germany a greenhouse, a polytunnel or a warm south facing wall makes the difference, and planting out should wait until after the mid May cold snap. Where summers are short, always choose the shorter cycle varieties and start them early in a heated tray. In Italy it is an easy crop: in the centre and south plant from April onwards and the only real care is light shade through the July and August heat; in the Po valley and the north wait for the late frosts to pass and pick the sunniest spot you have.
Fertilização
Its needs are moderate. One to two kilos of mature compost per square metre worked in before sowing covers most of the cycle. If the leaves pale, one watering with a balanced liquid organic feed halfway through is enough. Never use fresh manure, which burns roots and encourages disease.
Rega
Water regularly for the first weeks, then less often but deeply so the root goes down. Step it up at flowering, the phase of greatest need. Once established it is remarkably drought resistant.
Controlo de Infestantes
Hand weed in the first weeks, while the plant is small and loses every contest for light and water. Once it is established, mulch with five to seven centimetres of straw, dried grass or leaves: it holds weeds back, keeps moisture in and stops rain splashing soil onto the lower leaves, which is how most diseases begin. Always hoe shallowly so you do not cut the roots running just under the surface.
Controlo de Pragas
Birds are the main problem, at sowing and later on the ripe head: cover the seed at sowing and bag the heads with mesh once the seeds start to fill. Aphids and thrips attack the young leaves. Slugs eat the seedlings. Head caterpillars bore into the centre in hot years.
Doenças
Downy and powdery mildew affect the leaves in humid conditions. Sclerotinia rots the stem and head and is the most serious disease, favoured by wet soil and short rotations. Rust makes orange pustules. Use a four year rotation and do not repeat sunflower in the same bed.
Colheita
For cut flowers, cut when the head is opening and the petals are still fresh, in the morning. For seed, wait until the back of the head turns from green to yellowish brown and the bracts dry; cut the head, hang it somewhere dry and airy and thresh once fully dry. Leaving it too long on the plant means losing the lot to the birds. Allow about 100 to 120 days from sowing to the first harvest of this variety. The reference colour is yellow with a brown centre, and that is what tells you it is ready.
