Sunflowers always face the sun, which means they must turn from east to west every day. So what do they do at night? Do they shift back at sunrise or gradually through the night or what?
-- Rachel, San Diego
Grandma Alice learned a big sunflower lesson a few years ago, so she's the perfect person to ask. Sounds to me like they'd eventually twist their flowers off and die, but Grandma says otherwise. And we're talking here about the six-footers with the huge seed heads.
Between the time a sunflower sprouts and the time the flower blooms, the leaves and flower bud do follow the sun from east to west. There's a plant hormone that is created on the shady side of the stem in each day's growth, and this causes the stem to twist slightly. After dark the hormone moves throughout the plant, the tension in the stem is released, and the bud and leaves slowly return to their original positions, ready for sunrise. Because sunflowers grow very fast, the hydrodynamics are easy to see. But once the plant has reached full height and the flower blooms, it faces east and never moves again. Why east? Botanists guess: less sun stress?; early-morning sunlight to dry moisture and keep seeds from rotting?; sheer orneriness? The lesson Grandma learned is, don�t plant your sunflowers on the east side of the house because all you'll see will be their backsides. The neighbors liked them, though. Grandma was really teed.