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Why do sunflowers follow the sun? This mystery has been researched and hopefully solved. Recently, discoveries at UC Davis have explained what this movement is and what causes it. The tracking was reported in the magazine Science, and it’s known that the movement follows circadian rhythms.

We humans have these internal clocks as do sunflowers and other plants. The sunflower rotates as different parts of the stem change shape during the day. Once the flower is mature, it no longer moves. This movement is called heliotropism.

Sunflowers are native to North America. There is evidence that the Native Americans of Arizona and New Mexico knew them and used them in food and food preparation 3,000 years ago.

When the Spanish arrived around 1500 AD, they sent seeds back to Europe where they were planted in gardens. By the 18th century, sunflower oil had become popular and Russian farmers were planting thousands of acres for oil.

North American farmers initially grew sunflowers as poultry feed. In 1930, Canada spearheaded the first official government-sponsored sunflower-breeding program.

Today, sunflowers are grown in many countries, with Russia and Ukraine leading the way. Sunflowers are also a major crop in the U.S. When you drive to Sacramento in summer, you will see vast fields of sunflowers along Interstate 80.

Sunflowers have been developed to thrive in home gardens. If the heads are huge, as many are, they hang down. When I grow them, the birds love perching on the edge of the flower and eating the seeds. The heads are actually composed of many small flowers that produce seeds when ripe.

It’s easy to grow sunflowers at home. Often, birds will plant the seeds for you. There are both annual and perennial sunflowers and both types attract bees and birds.

The plant has a long tap root, so if you want the “tallest in town” variety, plant directly into the soil. Sunflowers need full sun and nutrient-rich soil. They also require deep watering, especially when first planted. Be aware that they will shade plants near them so site them where that won’t create a problem.

I love the many sizes and colors of modern sunflowers. U.S. breeders have done most of the hybridizing. Some varieties reach 10 feet in height, while others are small enough to use for table décor. Breeders also have come up with sunflowers that don’t produce pollen.

Sunflowers with black seed are the ones harvested for oil. The seeds are edible, either by the birds or by the grower and friends.

How you plant sunflower seed is important. Choose a site that gets several hours of sun each day. Also take into account the plant’s mature size. Plant giant sunflowers in the back of the bed and smaller ones near the front.

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For the best results, sow seed directly in the garden soil. Transplants don’t do as well. Plant seed about 1/2-inch deep and, depending on the size of the mature plant, about a foot apart. Tap the soil down and water well after the seed is in place and about once a week thereafter. Irregular watering will reduce the size of the flower head.

Some gardeners fertilize sunflowers regularly. I usually put them in fertile soil well-amended with compost and don’t worry for the rest of the summer.

The biggest obstacle you will face is keeping critters off the seed heads. You can tie large paper bags or burlap over the flower and keep the covering in lace until the seeds are ripe.

If you want to roast the seeds, take them off the head, soak in salt water for 24 hours, dry them and then roast for 30 to 45 minutes at 300 degrees Fahrenheit. Add oil or butter to your taste.

Workshop: The UC Master Gardeners of Napa County will present a workshop on “Growing Spring and Summer Vegetables” on Saturday, March 9, from 9:30-11:30 a.m., at the UC Cooperative Extension, 1710 Soscol Ave., Napa. Do you want nutritious, easy-to grow, fresh food from your garden this spring and summer? Learn what the garden needs to successfully produce spring and summer vegetables from seeds and plant starts. In addition to growing basics and hands-on activities, this program includes watering, fertilizing and harvesting tips, with a dash of integrated pest management for pest and disease control. Online registration (credit card only); mail-in/walk-in registration (check only or drop off cash payment).

Workshop: The UC Master Gardeners of Napa County will present a workshop on “Summer Vegetables” on Sunday, March 10, from 1-3 p.m., at Yountville Community Center, 6516 Washington St., Yountville. Learn some basics, get keys to success, and do hands-on activities to learn about new varieties and review old favorites. Online registration or telephone the Parks & Recreation Department at 707-944-8712.

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UC Master Gardeners of Napa County (napamg.ucanr.edu) answer gardening questions on Monday, Wednesday and Friday, 9 a.m. to noon, at the UC Cooperative Extension office, 1710 Soscol Ave., Suite 4, Napa, 707-253-4143, or from outside Napa toll-free at 877-279-3065. E-mail your garden questions by following the guidelines on the web site. Click on Napa, then on Have Garden Questions?