|Germination||Sow the seeds thinly, at about 12mm ½ in. deep, 30 cm apart in well cultivated soil raked to a fine tithe. Germination usually takes around 21 days. Once the seedlings are large enough to handle thin the plants to 30cm (12 in) apart. Alternatively, you can sow indoors in late winter/early spring for earlier flowering. Sow the seeds individually, into 7.5 cm (3 in) pots at a temperature around 20-30C (68-86F). Once they are well grown, gradually acclimatize them to outdoor conditions, before planting out, after all risk of frost.
Notes: What is usually called the flower is actually a head (formally composite flower) of numerous flowers (florets) crowded together. The outer flowers are the ray florets and can be yellow, maroon, orange, or other colors, and are sterile. The florets inside the circular head are called disc florets. The disc florets mature into what are traditionally called "sunflower seeds", but are actually the fruit (an achene) of the plant. The true seeds are encased in an inedible husk.
Sunflowers in the bud stage exhibit heliotropism. At sunrise, the faces of most sunflowers are turned towards the east. Over the course of the day, they move to track the sun from east to west, while at night they return to an eastward orientation. This motion is performed by motor cells in the pulvinus, a flexible segment of the stem just below the bud. As the bud stage ends, the stem stiffens and the blooming stage is reached. Now the stem is frozen, typically in an eastward orientation. The stem and leaves lose their green color. The wild sunflower typically does not turn toward the sun; its flowering heads may face many directions when mature. However, the leaves typically exhibit some heliotropism.
|Scarification / Stratification||No|
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