How Does a Sunflower Grow & Develop?

Germination

• Sunflower seeds germinate when planted in warm, moist soil. The optimum planting depth is about 2 inches, or 1-1/2 inches for dwarf varieties. In moist conditions, the seed covering splits open, and the sprout inside unfolds and grows up toward the soil surface until it emerges into the light. The sprout has two cotyledons, or seed leaves, allowing the tiny plant to begin photosynthesis, using light from the sun to create energy. Coupled with nutrients garnered from its tiny roots, this energy powers further growth and development.

Vegetative Growth

• The plant achieves vegetative emergence when the first leaf beyond the cotyledon appears. Later vegetative stages are named for the number of true leaves longer than 4 cm present on the plant. A plant with one true leaf is termed stage V-1; two leaves is V-2; three leaves is V-3, and so forth. Leaves appear radially on a tall central stalk, with each new leaf bud appearing above its predecessor. The plant stops producing new leaves when the flower bud appears.

Flowering

• The terminal bud on the top of the plant forms the flower. Considered the reproductive stage of the plant and labeled R-1 through R-6, the formation of the flower starts with a small bud (stage R-1) on a stem that continues to grow about an inch above the top leaf (stages R-2 and R-3) before opening (stage R-4). The outer petals form the ray flower, surrounding the smaller disk flowers (stage R-5) that will eventually become individual sunflower seeds. When flowering is complete, it begins to wilt (stage R-6).

Seeds

• Fertilized disk flowers on the sunflower grow into seeds, starting from the outside of the flower head and moving inwards as the plant matures. The progress of the seed formation is tracked and labeled according to the color of the back of the flower head, which starts out green. In stage R-7, the back of the head begins to turn yellow. In stage R-8, it is almost completely yellow. In stage R-9, the plant is mature and ready for harvest, and the back of the head is completely yellow and brown.