When is the latest blooming time for sunflowers?
The sunflower is a large annual plant of the genus Helianthus in the Asteraceae family that can grow up to 3 m tall. It gets its name because its flower often faces the sun. Besides its appearance resembling the sun, its bright and generous flowers are very suitable for ornamental display. Its seeds are called sunflower seeds, often roasted and eaten as a snack, and they can also be pressed into sunflower seed oil. Now let us take a look together at when sunflowers bloom!
When do sunflowers bloom?
Sunflowers are usually sown from March to April and bloom from July to August. Sunflowers can bloom in all four seasons, and the secret is “accumulated temperature”, that is, as long as the plant accumulates a certain amount of temperature during growth, it can bloom. For a sunflower head, from the opening of the ray florets to the completion of the opening of the disc florets generally takes 6 to 9 days. From the second day to the fifth day is the full-bloom stage, and the number of flowers opening in these 4 days accounts for about 75% of the total number of opened flowers. The flowers mostly open from 4 to 6 in the morning, and pollination and fertilization occur on the morning of the next day. Unfertilized flower heads can remain without wilting for 7 to 10 days.
The growing environment of sunflowers
1. Temperature: Sunflowers are a crop that likes warmth and is also tolerant of cold, with strong adaptability to temperature. The seeds have a very strong tolerance to low temperature. When the soil temperature is stable above 2°C, the seeds begin to germinate; at 4 to 5°C they can sprout and take root; and when the soil temperature reaches 8 to 10°C, it can meet the needs of seed germination and emergence. Throughout the entire growth period of sunflowers, as long as the temperature is not lower than 10°C, they can grow normally.
2. Water: Sunflowers are a crop that consumes a relatively large amount of water. The plants are tall, with many dense leaves, and their water uptake is 1.74 times that of corn. However, because their growth and development are mostly synchronized with local rain and heat, the contradiction between water supply and demand is not prominent, and the water requirements differ greatly at different growth stages. From sowing to budding, the water requirement is not great; from budding to flowering is the peak water requirement period; and from flowering to maturity, the water requirement is also relatively large.
3. Light: Sunflowers are a short-day crop and are not very sensitive to daylength. They like sufficient sunlight, and their seedlings, leaves and flower heads all have strong phototropism. With sufficient sunlight, the seedlings are robust and can be prevented from excessive vegetative growth. With sufficient sunlight in the middle growth period, vigorous stem and leaf growth can be promoted, normal flowering and pollination can occur, and the seed-setting rate can be increased. With sufficient sunlight in the later growth period, the seeds are plump and full.
4. Soil: Sunflowers have relatively low soil requirements and can grow in all kinds of soils, from fertile soil to dry land, barren land and saline-alkali land. They not only have a relatively strong tolerance to saline-alkali conditions, but also have salt-absorbing properties. At the same time, sunflowers have well-developed root systems and relatively strong drought resistance. Moreover, the roots and stems of sunflowers have well-developed aerenchyma, making them very tolerant of waterlogging.
The growth cycle of sunflowers
1. Seedling stage: From emergence to budding, sunflowers are said to be in the seedling stage, generally requiring 35 to 50 days, or 28 to 35 days for summer sowing. This period is the stage of leaf and flower primordium formation and floret differentiation. The seedling stage of sunflowers is the stage with the strongest drought resistance. Aboveground growth is slow, while underground root growth is faster, quickly forming a strong root system.
2. Budding stage: From budding to flowering, sunflowers generally need about 20 days. This is a period when vegetative growth and reproductive growth proceed together, and it is also the most vigorous stage in their life. During this period, the demand for fertilizer and water is the greatest, accounting for about 40 to 50% of the total fertilizer and water demand. If the need for water and fertilizer cannot be met in time, yield will be seriously affected.
3. Flowering stage: For a sunflower head, from the opening of the ray florets to the completion of the opening of the disc florets generally takes 6 to 9 days. From the second day to the fifth day is the full-bloom stage. They mostly open from 4 to 6 in the morning, and pollination occurs on the morning of the next day. Unpollinated flower heads can remain for 7 to 10 days, but the seed-setting rate of self-pollination is only about 3%, while the seed-setting rate of cross-pollination is high.
4. Maturity stage: The maturity stage of sunflowers refers to the stage from flowering to maturity, 25 to 55 days for spring sowing and 25 to 40 days for summer sowing, with differences among varieties. About 15 days after flowering and pollination is the seed formation stage. The maturity stage of sunflowers requires clear weather, a relatively large temperature difference between day and night, and suitable soil moisture.