- Sunflower plants (Helianthus annuls) thrive in rich, well-drained soil and full sun exposure. Depending on their variety, Depending on their variety, these quick- growing annuals may reach heights of 10 to 15 feet and produce dinner plate- size flower heads. Some dwarf varsities top off at less than three feet and have small blooms. The flower head of a young sunflower tracks the arc of the sun as it moves across the sky but the flower head of a mature sunflower typically faces east.
- Many plants are known for their ability to track the movements of the sun by a process called solar tracking or heliotropism. A young sunflower’s flower head faces the sun to receive the sunlight it needs for photosynthesis. Heliotropism is the term for a plant’s ability to follow the sun. That ability allows a sunflower to move with the sun as it arcs across the sky from east to west; the sunflower's bloom always faces the sun. Sunflowers turn their faces toward the sun as they track it across the sky.
- Special motor cells at bases of the flower buds shrink or enlarge as they absorb the water, which moves their faces toward the sun. This is the same way that many other flowers track the sun. And the sunflower doesn’t stop tracking the sun after the sun dips below the horizon. The sunflower’s bloom continues to move until it faces east, put the flower head in position to catch the sun’s morning rays. Some- times, the flower faces east before the sun fades completely in evening.
- Once a sunflower is pollinated, it ceases solar tracking. This supports the idea that the reason sunflowers turn their flower towards the sun is for the warmth, which attracts pollinating insects. Another possibility is that the sunlight aids the development of pollen. It’s a different type of sun tracking than their leaves and the foliage of many other plants perform. Leaves track the sun to absorb light for photosynthesis. Heliotropism most likely helps to increase the development of pollen – Once pollinated the sunflower head remains facing east.
- Immature flower buds of the sun flower do exhibit solar tracking and on sunny days will track the sun across the sky from east to west and by dawn the buds will have returned to face eastward. However, as the flower bud matures and blossoms, the stem stiffens and the flower becomes fixed facing the eastward direction.
- When the sunflower plant matures, the neck of its stem no longer grows, and tracking of the sun’s arc ceases. The blooms of most mature sunflowers face east, but some face other directions.
- Mature sunflower buds and opened blooms become fixated on the east, with only their leaves continuing to track the sun for photosynthesis. This happens in part because in part because the stem stiffens, making it less possible for sunflower faces to turn and stretch toward the sun. Once and flowers form seeds, they no longer practices heliotropism.
- When plating a sunflower, place it where you’ll be able to see its flower head when the plant matures and is in full bloom. For example, plant the sunflower on your yard’s western or northern side.
- Flowers of some plant species track the sun across the sky from east to west. A good example of this is the alpine plant, the snow buttercup (Ranunculus adoneus). By facing the sun, the flower of the snow buttercup is able to collection heat from the sun. The heats is thought to help pollination since the insect pollinators will warm and be able to fly better in the cold air and deliver pollen more effectively to other plants. The warmth also appears to help the pollen germinate after it is delivered to another flower.
