Sunflower Power

Bright and cheerful, sunflowers are the happy face of the plant world.

April 10, 2012

Although sunflowers (Helianthus annuus) have a corporate side—as a cash crop for their edible seed and oil, and as the highlights of pricey floral arrangements—their nearly universal appeal to gardeners may rest solely on the fact that just looking at them can make you happy.

They're so easy to grow, squirrels and birds can sow a healthy crop by accident underneath a bird feeder. Varieties thrive largely as annuals in all USDA Plant Hardiness Zones, from Alaska to Hawaii. After all, this plant, made iconic by Dutch painter Vincent van Gogh, was first cultivated in the American Southwest around 1000 B.C. and developed for commercial use in the mid-1800s in Russia, where brutal winters stymied grand armies. Today, Russia, Ukraine, and below-the-equator Argentina are among the largest growers of sunflowers in the world.


Yet unless the goal is growing a cash crop, or setting Guinness World Records for tallest sunflower or biggest sunflower head, sunflowers require minimal care. That's a miracle, since sunflowers are a native American plant, "so the largest number of pests co-evolved with them," notes Jim Shroyer, Ph.D., extension crop specialist at Kansas State University. These pests' long and close association with the plant is reflected in their names: sunflower moth, sunflower midge, sunflower headclipping weevil, and sunflower maggot. Many of them are a big problem in Kansas, the Sunflower State, where the Helianthus is the state flower and about 2 percent of agricultural acreage is dedicated to sunflowers. (Then again, wild sunflowers are so plentiful in Kansas "they're considered a weed," says Shroyer.)

But in the home garden? "Mostly, all you see is a little rust," says Venelin Dimitrov, product manager of flowers at Burpee, in Warminster, Pennsylvania.

Sunflowers have a very short growing season, going from seed to towering flower in about 2 to 3 months. Under the right conditions, they can grow 12 inches in a day, because of the efficiency with which they harness the sun's energy. Sunflowers are phototropic. In their bud stage, they faithfully follow the sun, which increases light exposure and photosynthesis. "After pollination, the disk faces down and east permanently to protect the seeds from solar radiation," says Dimitrov.

Despite their bright collars of petals, sunflowers, which come in single- and multistem varieties, aren't really single flowers but 1,000 to 2,000 individual flowers. The ray petals around the circumference have no stamens or pistils. Their function is to attract pollinators to the landing pad or "disk," since sunflowers rely heavily on bees and other pollinators to reproduce, says Dimitrov. Pollenless hybrid varieties were developed for the cut-flower industry (to avoid that "messy" yellow dust), so they're starlet pretty and a boon to the allergic gardener.

Sunflowers can grow just about anywhere. "You'll see them by the side of the road in New Mexico growing right through the pavement," says Dimitrov, who grew up in Bulgaria, where he recalls acres of golden sunflowers dotting the landscape every summer.

But they do have a few picky requirements. They prefer 6 to 8 hours of direct sunlight—even more if the purpose is record-breaking growth. Without it, plants grow spindly and fall over. Sunflowers are also heavy feeders, so it's best to plant in compost-enriched, well-drained soil after all danger of frost has passed, when the soil temperature is at least 50°F. Direct-sow seeds (to a depth of 1/4 to 1 inch) every couple of weeks to ensure a bumper crop through fall. Sunflowers are only middling drought-tolerant, so they may need some judicious watering throughout the season.

With enough sun, though, sunflowers can do multiple duty in the garden: attracting birds and bees; feeding birds; providing snacks, bouquets, and beauty; or offering support for other plants, like tomatoes, as a kind of green, living stake. The seeds are also a natural herbicide, as anyone who has tried to grow grass under a bird feeder will know. And they work similarly to cover crops, returning macronutrients to the soil. Birds may become an enemy when seed heads appear—especially if a gardener's goal is harvesting the seeds for snacks. Sunflower seeds are an energy-dense food for seed-eaters, winged and otherwise. In some varieties, about 40 percent of the weight is oil, which is very high in vitamin E. Sunflower seeds are also rich in thiamine (vitamin B1), a number of minerals, and phytosterols, chemicals that have been linked to lower cholesterol.

But, warns Dimitrov, birds also love the tender shoots that start appearing less than 2 weeks after planting. "Those young sprouts are very tasty," he says. "Birds usually go after seedlings at the two to four leaves stage, but after that they leave them alone. The plants are fast growing, so that helps. The only thing you can do is sow extra seed. Hanging old CDs is an innovative way to scare the birds, or have fun with the kids by creating scarecrows." Protect the seed from the birds by covering the heads with burlap when the disks start to fill in, advises Dimitrov.

Cut sunflowers for bouquets from the time the bud appears. The first sign that seed is ripe for harvesting is when sunflowers stop being sun worshippers. Their heads droop, the inner flowers easily rub off, and the outer petals have clearly called it a day. The back of the seed head should be a lemony yellow color. Check a few seeds to make sure they contain a kernel. If it looks like a go, remove the entire head and place it in a bag or cheesecloth and hang it in a cool, dry, dark place to dry further. After about 2 weeks, the seed should be ready for roasting—or for the bird feeder. For human snacks, place seeds in a shallow pan and roast at 300°F for 30 to 40 minutes.

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