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|If growing sunflowers from seed indoors ahead of time, use peat pots, which are ideal for plants like sunflowers that don't like to be transplanted. Sow two seeds per pot and cover them with plastic to keep them moist. Place them under grow lights, or a sunny windowsill, or a greenhouse.
Once seeds germinate (10 to 14 days), pinch out weakest plant, so you have one per pot. Give seedlings bright light and water and fertilize regularly. In mid-May, harden off your sunflowers. Plant the young plants into your garden, pot and all (the roots will grow through the peat) after all chance of frost is over.
Alternatively, you can sow the seeds thinly outside, « in deep about 12 in apart, in a well cultivated soil, after the danger of frost has passed. Once the plants are about six inches tall, thin them to 2 to 4 ft apart, to give individuals space to spread.
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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