 |
ProCrop |
Sunflower Frost Tolerance
Sunflower is most susceptible at the bud and pollination stages (R5) of development. Temperatures of 30 degrees F or less can cause damage to the anthers and stigma's of the pollinating disk flowers.
The sunflower has a composite type flower. Several rows of showy yellow ray flowers encircle the head and are commonly called the "petals", though each is an individual flower. The center portion of the head, and by far the greater part, is composed of inconspicuous individual flowers, one for each seed that may develop. These flowers mature in circles from the outside of the flower head to the center, so that at various stages, the flowers ready for pollination appear as a yellow circular band in the brownish or dark center of the head. It is these disk flowers that are sensitive to frost.
The result of frost in the flowering period, then, could be circular bands of undeveloped seed that would vary with individual flower heads from band around the outside edge to a spot in the center. Unopened buds are less susceptible to frost than the opened flower heads. Growers can determine the extent of injury by cutting the surface of the flower head.
Once pollination is completed and 10-14 days after petal drying occurs, the sunflower plants can withstand frost temperatures as low as 25 degrees F and have only minor damage. Twenty-five degrees at the bud stage will often damage stalk below the bud and seeds will not develop. If hard frosts do occur, then many time only the seed in the center of the head (the last to pollinate) will be affected.
Back to Sunflower Menu
Back to Main ProCrop Index
