I notice that when commercial sunflowers are planted, two rows are of shorter plants and three rows are of taller, larger-headed plants. I've always been told that the short plants were male and the tall plants female, but, while not particularly self-pollinating, a sunflower is supposed to have both male and female components. The two rows of shorter plants are sprouting first. Question 1: why the two different types of plants? Question 2: why do the shorter plants sprout first? Planted first? Not planted as deep? Need to mature first?
Yolo County California
Dear Sir/Madam Commercial sunflowers these days are hybrids and self compatible and therefore self pollinating. Sometimes bee hives are added to assist this process. If you are seeing lines of both short and tall sunflowers in a block, this will be a seed production or crossing block where hybrid seed for a commercial cultivar is being produced. The shorter males may be planted a bit earlier than the female lines to ensure plenty of pollen is available when the taller female single headed lines are flowering. The shorter male lines may be multi headed. Bee hives are often also present nearby to assist pollen transfer. The female plants are male sterile ( no pollen) and need the pollen from the male line to produce a seed. This crossing process creates hybrid seed in the female head for planting commercially. The male plants will usually be cultivated out as soon as pollination of the females is complete. The fertilised females stand alone in the field until maturity when they are harvested. Sue Thompson. Sunflower Pathologist. Research Fellow USQ. Toowoomba Qld. Australia.