Why Are Some Sunflowers Dark in the Center?

Features

• Sunflowers grow toward the sun. They are heliotropic, meaning that their heads turn to the sun until the stems become so stiff that the flower is no longer flexible enough to follow the sun's path across the sky. They grow rapidly from seed and, depending on the variety, grow from under 1 foot up to 10 or more feet tall in a season. Sunflower heads range from 3 inches to over 1 foot in diameter. The heads are composed of tiny flowers in the center. These center-disc flowers are usually yellow or brown.

Uses

• Sunflowers form attractive garden borders. They draw birds and pollinators to the garden, tacitly encouraging birds to eat bugs while in the vicinity and bees to pollinate nearby plants. Sunflower seeds, an important food crop, attract birds and wildlife as they mature and fall to the ground. The summer-blooming flowers are popular as cut flowers. Some varieties have reddish petals with dark brown centers, providing unusual sunflower color in wildflower arrangements. Dwarf sunflowers, many with two-color flowers and dark centers, grow in container gardens.

Maturity

• Most sunflowers, even those with yellow floret centers, eventually darken in the center. As the sunflowers mature, the tiny disc flowers fall off and reveal seeds forming in the center disc. The seeds are light or green in color, and then mature into tan and dark brown hard-hulled seeds. These seeds expand and fill out the center as a dark bulging sunflower head, while the yellow outer-ray petals shrivel away. The dark seed-packed head eventually bends over from the weight.

Harvest

• When the back of the sunflower head turns dark and the seed head bends over toward the ground, birds and other animals flock to the sunflowers. Seeds begin to loosen and fall to the ground as the ray flowers shrivel. Birds eagerly rip into the plant, often hanging upside down on the seed head to pull out ripe seed hulls. Protect the seeds by covering the entire flower head with cheesecloth, a pillowcase or other fabric that collects seeds as they fall and keeps birds off the disc. When the head is dry, cut it off the plant and rub off the ripe seeds, or put the head in a protected area until the seeds readily fall from the dried flower.