Do Sunflower Plants Die After Flowering?

Why Sunflowers Die

• Sunflowers as living organisms have a built-in lifespan. They strive to reproduce their kind before their life is over. Annual plants like sunflowers evolved a "one shot" reproductive strategy in which they sprout, grow, flower, go to seed and die off all in one growing season. This way, parent plants won't compete with their offspring. Some scientists believe the process of pollination and seed formation triggers hormonal changes in annual plants, sending a "signal" that it's time to die. Gardeners have long known you can prolong blooming of annuals by nipping off mature flowers before seeds form.

Planting Sunflowers

• Sunflowers will grow in a wide range of soil types, but the soil must be well draining. High-nitrogen fertilizer helps growth and seed production. They are grown from seeds in temperate regions and require about 110 days from planting to maturity. Sunflowers can be planted in early spring, but they need soil temperature above 40 degrees Fahrenheit to germinate. Young plants can tolerate light frost but will die if temperature falls below 28 degrees Fahrenheit. Plant your sunflowers in mid-March to early April in the Southern U.S., and May 1 to May 20 in Northern states. Plant seeds between 1 inch and 3.5 inches deep, depending on soil type. Plant seeds about a foot apart in rows about a yard apart.

Growth Habits

• Sunflowers grow to about 6.5 feet tall, with an underground tap root about as long as the above-ground stem is tall. Stems are round with plants are young but become angular and woody at maturity. Stems normally don't have branches. Plants form a single large yellow bloom at their top. Sunflower leaves and blooms turn during the course of a day to follow the sun's rays, resetting at night. The sunflower bloom isn't a single flower. It's actually made up of 1,000 to 2,000 tiny individual flowers sharing a common receptacle. Sunflowers can pollinate themselves, but produce more seeds if cross-pollinated from neighboring plants by insects.

Pests and Diseases

• Sunflowers are prey to three types of moth larvae that feed on flowers, stems and seeds, four species of weevils that eat seeds and stems, a beetle whose larvae eat the leaves, a fly maggot that attacks stems and a midge that attacks the flowers. There also are seven fungal sunflower diseases that attack flowers, leaves and stems. Commercial growers use pesticides and fungicides against these scourges. Birds can be major pests of sunflowers. Blackbirds, finches, doves, grosbeaks and sparrows are very fond of sunflower seeds. Commercial growers use a variety of techniques to scare off bird pests.