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I read somewhere online that sunflower blossoms always face east; but recently I read elsewhere that the blossoms move over the course of the day so they are always facing the sun. Which is it?
According to Wikipedia, they do indeed follow the sun. They begin the day facing east and track the sun all day until they face west by nightfall. At night they reorient their flowers to once again face east. I had always heard they followed the sun and you got my curiosity up!
Me the same as the other 2 gardeners, in fact, when I was a kid, I used to just stick the PLANTS in any old way, some had the flower buds facing the wall as I never knew different then, and was amazed to find they had turned there heads around to face the sun, My Grandkids get to make smiley faces on the large flowering sunflowers by using tweezers, they just pluck out the eyes and mouth either smiling or sad, they sure are a conversation piece when people notice the faces, and it's fun too. good luck with your sunflowers. WeeNel.
The phenomenon of plants "following the sun" (phototropism) is actually neater than you realize. The chemicals that regulate plant growth are repelled by sunlight and therefore move away from it to the opposite side of the plant. This causes the plant to stretch a little bit more on the darker side of the stem and in turn, the stretching pushes the bright side of the stem towards the sun. This is very oversimplified explanation (and it's so much easy to explain with a diagram) but it's still super-cool!
Well, actually it's both. First, not all sunflowers are phototropic. It's usually the sunflowers with a single-head (the ones with many heads facing in all directions their heads don't move with the sun).
The phototropic ones only follow the sun for a period. When the sunflower is growing the stem & material is soft and pliable, the unbloomed bud is light and will follow the sun during this phase. However, when the sunflower blooms the sunflower slowly stops growing, instead putting the energy into the seed head. At this point the rest of the sunflower (stem, etc.) starts to solidify, and will eventually solidify facing in an eastwardly direction and the bloom will no longer follow the sun. So, the phototropic ones do follow the sun but only for a time and once bloomed will eventually "freeze" facing in an eastwardly direction.
My guess is, they solidify as a mechanism to help support the head which gets bigger and heavier once bloomed. If they didn't solidify they would eventually collapse under the weight of the seed head as it matures.
