Helianthus Tosca is suited for greenhouse- as well as outdoor-production and can be grown on almost any kind of soil. Soil types with a high organic matter sometimes give a too stark growth, which means a very tall plant with big leaves.
For outdoor production sowing is possible from end of February, protected with film cloth or perforated foil, until the third week of July. This means a week later than most other varieties of Helianthus. Sow in 4 rows in beds of 1,20 m wide. The quantity of seeds in a row varies strongly. More than 30 plants per m2 is not recommended. The plant is commonly supported by wire. For large scale production, wire is not used and plants are sown rows with a distance of 50 or 75 cm. between the rows. Depending on the distance between the rows the distance in the row is 8 to 12 cm. Usually 12 to 20 seeds per m2.
Sowing can be done from the beginning of January until mid April and from mid July until the end of August. After mid April sowing is not recommended because of competition with outdoor production. When sown in late autumn, it is possible that because of a shortage of light in the winter months, the flowers will not develop completely. As soon as the first leaves show a day length of 16 to 17 hours is recommended. After the third and fourth pair of leaves are formed darkening is done. In spring and autumn day length is kept on 12 hours. If sowed in week 8 until week 11, there is a natural short-day circumstance and no greenhouse with artificial darkening is needed.<br />After the flower buds are formed artificial light is given during 16 to 17 hours, to speed up the flowering. Usually 25 to 35 plants per m2 are planted. The optimal germination temperature is 18 degrees. After 3 weeks the temperature can be lowered. Make sure that the temperature during the day is higher then during the night to make the flower stems stretch. Make sure that the relative humidity is not too high and the greenhouse temperature doesn’t increase too fast and too high in the morning!