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|Nom commun||Giant Sunflower|
|Germination||Sow the seeds outside from March to May. You can also sow indoors at a temperature around 68-86ø (will germinate over a wide temperature range). Sow those 2-3 weeks before planting out. Sow at a depth of 4 times the size of the seed, and expect germination in 5-10 days. Transplant seedlings when there have, at least, two sets of true leaves. Grow on at 70-75øduring the day and 65-68ø at night. Once they get bigger, plant them out at 2-4 feet apart, in full sun and in a light soil. The seeds can be sown outdoors after last frost, but remember: they are a favorite food of birds and rodents and may be eaten by them! Germination can take longer. Be patient!
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.
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