Bob Koenders shares pointers on how to best grow this popular flower

Photos by Sandie Parrott
Bob Koenders demonstrates how to cut sunflowers: strip the lower leaves and cut diagonally with a sharp, clean boxcutter, and place immediately in water with preservative.by Sandie Parrott

When Koenders married the love of his life, Judy, they used lots of happy sunflowers for their wedding. In fact, sunflowers and even sunflower bouquets for the bride are becoming more popular for weddings according to Koenders. Florists in the area didn’t even know they wanted sunflowers when Koenders started experimenting with varieties. “I grew about 50 different varieties until I found about 5 that I grow every year.” They are all the pollenless varieties. “Now the demand is so high, the florists are calling me!” he exclaims.

At dusk, a field of sunflowers begin to turn their heads toward the setting sun. Notice the hilled rows of soil that help support the heavy plants.A little bit of history

According to the National Sunflower Association, the wild sunflower is native to North America, but commercialization of the plant was done by Russia. It was only somewhat recently that the sunflower plant “returned” to America. Native Americans first developed the wild sunflower into a single-headed plant with a variety of seed colors including black, red, white, and striped black and white. Some archeologists suggest that sunflowers may have been domesticated before corn. The Native Americans used the sunflower seed for grinding into flour, trail snacks, purple dyes, body painting, ceremonial, and medicinal uses. Sunflower oil was used for making bread, as well as on skin and hair. The dried stalks were even used for building materials. 

The large Russian varieties are still available today. Names like ‘Mammoth Russian,’ ‘Russian Giant,’ ‘Tall Russian,’ and ‘Mammoth’ are all typical varieties sold as giant sunflowers, along with all the new American, European and Asian hybrids. Koenders says identifying sunflowers can be a problem—there are always several names for essentially the same plant. He advises purchasing seed from reputable sources if you want a plant that grows true to the variety.

This unopened bud of ‘Sunrich Gold’ is still too early to cut but still beautiful and pollenless like most of Koenders’ sunflowers.Cutting sunflowers

Giant sunflowers wouldn’t work well as cut flowers, according to Koenders. They would be difficult to sell, handle (you practically need a chain saw to cut them) and use in a vase (the stalks are too thick and long). Koenders’ goals for the ideal cut sunflower: no pollen, 1/2-inch thick stem of about 3 feet in length, straight with a perfect flower head (held high) about 3 to 5 inches across. A “perfect” flower means no disfiguration, consistent color, and no diseases or pests.

During cutting, most of the leaves are stripped in one quick motion, leaving only the large ones by the head, and then a sharp box cutter is used to swiftly and cleanly cut the stem at an angle by the plant’s base. Cut flowers go directly into a solution of preservative and bleach until he delivers them, usually within 24 hours. Koenders and his hardy workers cut 7 days a week, 1,000 to 1,500 stems a day, which is just under 100,000 flowers annually.

This ‘Sunrich Gold’ sunflower is open too far to be cut for the floral industry. It will be sold directly at a farmers’ market or roadside stand.Growing sunflowers for cutting

The process begins with purchasing F1 (first generation) pollenless seed of proven varieties from quality sources. “It is more costly, but the plants are far superior. Saving seed means genetic variance, which can be good or bad,” Koenders comments. “Reusing seed means colors and sizes vary from plant to plant and stems can be weak, since it is open-pollinated (uncontrolled pollination by wind, insects, or birds). For homeowners, give it a try—it is fun to see what you get, but I can’t afford the risk.”

The other big component is good soil, and his farm has wonderful lake bed loam. Koenders monitors his soil, testing it every one to three years, depending on diseases or pests during that time, not just because he is an agronomist, but to check the levels of nitrogen and other nutrients. “Nitrogen is important for sunflowers. Nitrogen leaches out, but too much makes them leggy with large leaves.”

Seeds are started April 1 in the greenhouse. Sunflowers germinate in cool temperatures (45 to 50 degrees), and starting in early May seedlings are planted in the field. Seeds are started and plants are moved to the field every 7 to 10 days for about 10 successive plantings. “We can’t have them all in bloom at once, since we can’t harvest and sell all at once,” says Koenders. A tip he shares is to mound up the soil around the base of the plant to help support the stem. He continues to mound the soil while they are growing to help support the plant and to bury weeds. The mounded earth can get as high as a foot by the time the flowers are cut. He cautions, however, to not cover any leaves. 

Plants are set close together (6 to 12 inches) for support and to keep the plant size manageable, but he recommends up to two feet in a backyard situation for larger flowers. Rows are about 3 feet apart for cultivation. Pruning is important for florist quality blooms. Koenders prunes excessively to produce the type of perfect flower you expect to see at the florist.

“Sunflowers have a bad reputation with some people. Although they are pretty, many people think they don’t last, heads droop, and the stems are too thick,” Koenders laments. “This is because some sunflowers are dry-shipped from long distances like South America with their foliage stripped off.” According to Koenders, local pollenless sunflowers should have thinner stems and heads held high, and last 7 to 10 days in a vase (out of direct sunlight).

So the next time you want to brighten one of your late summer or fall days, pick up some cut sunflowers. You now know what qualities to be looking for.

Sandie Parrott is a garden writer and photographer who lives and gardens in Oakland County, MI.

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Fun facts about sunflowers

• Sunflower’s scientific name is Helianthus; Helios meaning “sun” and anthos meaning “flower.”
• Sunflower heads track the sun’s movement; this phenomenon is called heliotropism.
• Sunflowers can grow up to 12 inches a day during the peak of the growing season. They are more photosynthetic than many other plants and better utilize the sun for growth.
• Sunflowers (certain varieties) yield up to 40 percent of their weight in oil.
• Sunflower stems were used as filling for life jackets.
• Sunflowers are considered a popular art form because of their “human-like” characteristics, such as the “head” and the similar height to humans. 
• Sunflower leaves are cupped to channel the water down the stem.
• Sunflowers were worshipped by the Aztecs.
• Sunflower heads consist of 1,000 to 2,000 individual flowers joined by a receptacle base. The large petals around the edge of the sunflower head are individual ray flowers which do not develop into seed.
• The world record tallest sunflower (25 feet, 5-1/2 inches) was grown in the Netherlands in 1986.
• The world record sunflower with the largest head (32-1/4 inches in diameter) was grown in Canada in 1983.
• The world record sunflower with the most heads (837) was grown in Michigan in 2001.

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How to grow sunflowers – Tips from Bob Koenders

Light – All day sun.

Soil type – Not particular about type, but must have good drainage. Ideal pH range is 6.5 to 7.5.

Moisture – Water to start seeds and seedlings; water older plants during dry spells; they are drought tolerant, but will wilt when they need water.

Seed depth – Approximately 1/4 to 1 inch deep; very easy to germinate and grow.

Soil temperature for germination – 45 to 50 degrees.

Sowing – Sow seeds in successive plantings for cut flowers throughout the summer and fall.

Spacing – 6-12 inches for smaller varieties and up to 24 inches for larger varieties; allow at least 3 feet between rows for cultivation and air circulation.

Staking – May be required, unless grown closer together or up against a fence. Mound soil around base to support plant.

Fertilizing – Watch the salts. Sunflowers are very salt sensitive.

Pinching – Useful for forcing side shoots or pushing all the energy into one head.

Cutting – Plants should be cut when the bud is just beginning to open and is showing a little of the petal color. Strip off most of the lower leaves but leave larger ones by the head. Cut at an angle with a sharp and clean tool. Put in water with preservative immediately.

Height – Ranges from dwarf plants of 1-2 feet to giants of 15 feet or more.

Colors – Available colors range from white and cream, to all shades of yellow through to orange, red and burgundy. Centers can be yellow, green, brown, black, and black and white.

Recommended varieties – Gold-orange: ‘Soraya,’ ‘Sunrich,’ ‘Pro-Cut’ and ‘Sonja.’ Burgundy: ‘Moulin Rouge’ and ‘Prado Red.’