From United Kingdom Sunflower Association
It is generally best to wait until the average daily soil temperature exceeds 7°C (at 10 cm). Typically, sowing dates are between 16 April and 5 May. Sunflower will not germinate in a cold soil, and only very slowly (up to 35 days) when the soil temperature is around 5°C extending the germination period increases the risk from soil pests and diseases.
Harvest will ideally take place during September but does run into October. Dates achieved at Boxworth have ranged from 18 September to 16 October. Harvest usually occurs when the seed has dried down naturally to 15 - 20% moisture.
The seed is at 30% moisture when the back of the head is yellow and the bracts have begun to turn brown. By 20%, the bracts are 75% brown, the back of the head is becoming mottled and 75% of the lower leaves are senescent. During ripening the crop loses all its leaves and eventually the whole plant becomes dark brown in colour. In this state the crop stands well and dries quickly after rain or during windy weather.
The late drilling date of sunflower allows the use of a stale seedbed, pre-drilling, the land can be sprayed off with a total herbicide. Herbicide choice within the crop is limited but an early post-drilling, pre-emergence herbicide can give good control. The crop can compete very effectively with weeds from about the fourth week after emergence.
Measures to prevent slug and pigeon damage should be taken in all crops.
The shorter varieties can be less than 1.5m tall and the taller ones up to 2m tall. Wetter seasons lead to taller crops.
The seed should never be stored wet as it can heat up and go mouldy.
Use of a drying floor is the safest method and the seed should be at a maximum depth of 1m. The best method of drying is to use cold air until the moisture content falls to 15%. The seed can then be cleaned and heat (using the same temperature as for oilseed rape) used to reduce the moisture to 9% for long term storage. The seed should be left for seven days to allow the seed moisture to equalise before drying again if necessary. Sunflower seed has a lint like coating that can easily be rubbed off to form a light oil bearing dust. If this is taken into the unprotected intake of a continuous drier there is a high risk of fire. Drying methods, which include any form of agitation or movement of the seed, should therefore be used carefully. A method that has proved successful is to reduce the bulk of the moisture on a floor dryer and then complete the operation in a continuous dryer.
No, UK suppliers are happy to source seed from the UK. A range of sunflower buy back contracts is available and can be either pool price or open price where the merchant markets the produce at a time agreed after harvest. It is also possible for the grower to produce a crop without a contact, though it is essential to have good contact with the market if best prices are to be realised.
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