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Published September 14, 2009, 09:36 AM

Minnesota’s kiwifruit dream may come to your backyard

The University of Minnesota Horticultural Research Center near Victoria, Minn., has cold-hardy kiwifruits under development. The area on the west side of the Twin Cities is a hotbed of horticultural thinking, with the Minnesota Landscape Arboretum nearby, as well as other orchards in nearby Chanhassen. The horticulture efforts here date to 1860s.

By: Mikkel Pates, Agweek

VICTORIA, Minn. — If your only contact with the University of Minnesota’s agriculture program is its grain or livestock research, you might be surprised to know the institution has a project for kiwi breeding.

The University of Minnesota Horticultural Research Center near Victoria, Minn., has cold-hardy kiwifruits under development. The area on the west side of the Twin Cities is a hotbed of horticultural thinking, with the Minnesota Landscape Arboretum nearby, as well as other orchards in nearby Chanhassen. The horticulture efforts here date to 1860s.

Kiwi is a novelty promoters think could have commercial potential for small producers in niche markets.

Bob Guthrie, a Roseville, Minn., geologist and environmental consultant by trade and a horticulturist by hobby. He’s one of the nation’s leading experts on kiwi and a volunteer curator for the U of M’s kiwifruit collection.

Guthrie, who has his doctorate in geology from the University of Nebraska, at one time studied with U of M horticulture professor Jim Luby, who had been grown kiwifruit in Minnesota. Luby got him started out here, and he’s in his 16th year, Guthrie says.

Guthrie is like a kid in a kiwi candy store, tucked among the rows of Minnesota apples, pears and other jewels.

Guthrie’s interest in kiwifruit started in 1990, when he moved to Maplewood, Minn., and started growing kiwi vines in his backyard.

“It was pretty shady yard and I was looking for a fruit that would produce in the shade,” he says.

He moved to Roseville in 1992 and expanded his work.

Guthrie says about 80 species of kiwi are known. A dozen have potential for commercial production. Two are cold-hardy to warmer parts of Minnesota and a third species, kolomikta, can survive throughout the state.

“A lot of backyard gardeners have them, but there isn’t a whole lot in commercial production,” Guthrie says. “We’re hoping that changes. We’re hoping people might try them on a small scale for farmers markets or pick-your-own.”

Before cold hardiness

Kiwi plants first were known as Chinese gooseberries. They grew wild in China near the new, famous Three Gorges Dam — the world’s biggest hydroelectric facility. Scottish missionaries acquired fruit and sent them to New Zealand. The New Zealanders successfully renamed the fruit in the 1950s, for their national symbol — a flightless kiwi bird. The name wasn’t patented, so now the kiwi is grown around the world.

While it seems like a novelty, people have been trying to grow kiwi in Minnesota since before 1892.

Back then, Samual Green, a U of M horticulture professor, wrote about experimental kiwis — then still known as Chinese gooseberries — were grown in Minneapolis. Green likely received Japanese plant material from Massachusetts. In the late 1800s, Alexander Graham Bell praised the fruit for its taste. Bell’s son-in-law, David Fairchild, later would play a role in developing the plant.

In 1905, Green’s plants failed when temperatures hit 20 below zero in the St. Paul area. Kiwi species grown then were thought to require two consecutive mild winters to flower. The plants “break bud” in April. Flowers come in late May and June and become fruit in late July to mid-October, depending on the species and variety.

“A lot of the U.S. material came from Sapporo, Japan, where the Olympics were held,” Guthrie says.

When Green died in 1910, his kiwi studies died with him.

Others at the time were interested in the topic.

Guthrie thinks that N.E. Hansen, the famous horticulture pioneer from South Dakota State University in Brookings, looked into the species but didn’t end up growing them.

Meanwhile, researchers in Ottawa were looking into cold-hardy kiwifruit, and some of this work happened nearby.

In 1931, the Morden (Manitoba) Arboretum — about 130 miles northwest of Grand Forks, N.D. — selected some cold-hardy cultivars. Kiwis were grown there in the 1920s and then in the 1960s and 1970s with some success.

Fairchild helped organize the U.S. Department of Agriculture’s Foreign Seed and Plant Introduction Office, now part of the Agricultural Research Service. Fairchild went on worldwide plant gathering expeditions and was responsible for making the first interspecies kiwifruit cross in 1923. Fairchild also sent Frank N. Meyer to eastern Asia, Russia, Korea and China, where he collected kiwifruits, among others. Other world travelers brought back seed, too.

In the 1960s and 1970s, Robert I. Smith, a USDA horticulturist for the department’s Plant Introduction Station, now an experiment station in Chico, Calif., selected kiwifruit cultivars and helped commercialize kiwifruit in California.

“One of the problems in Chico was that most of the plants turned out to be male,” Guthrie says. “Part of it was they didn’t know much about it — how to grow them. They often grew them in the wrong locations.”

Either male or female

In the 1980, Americans became interested in kiwifruit.

“There wasn’t in the literature the best understanding, as far as care and management,” Guthrie says. “In the late 1980s, there was a big price crash. People were overproducing kiwifruit — more than the market could bear at the time.”

Kiwi plants are mostly either male or female. The female plants produce berries and males supply pollen.

Plants can be grown from both seed or cuttings. The cuttings assure that the plant will be either male or female. One male plant can produce the pollen to handle about six female plants.

Many kiwifruit continue to have the traditional bristles. Other varieties have a kind of “peach fuzz” or are smooth-skinned. Most smooth-skinned berries in the cold-hardy species are an “emerald” green, but some are reddish purple, red, orange or yellow, and some have longitudinal ribbing and striping. The berries range from round to egg-shaped.

The kolomitka species is a cold-hardy type — generally with good to excellent taste and flavor, with a sweet-tart characteristic, with berries in the 2- to 7-grams range. They yield up to 15 pounds per plant. Plants are spaced every 6 to 10 feet and don’t do well in full sun. Kiwi benefit from nitrogen and potassium. Light applications can be broadcast around the trunk areas after frost-out to early July.

According to Guthrie, the plants are best shaded from afternoon sun and winter sun — typically placed to the north or east of a tree line. Cooler, moister soil is favored.

“They like a lighter soil — not a loam, but a silt-loam or silt-clay loam,” Guthrie says. “They like a lot of organic matter. You can keep them on a 4-inch layer of woodchips.”

Cooler soil and air temperatures delay bud break in the spring and retain soil moisture. The bests sites are sloped and aren’t in low-lying, frost-prone pockets.

They do best in well-drained, aerated soil that retains moisture. Soil that is rich in organic matter and slightly acid to neutral is best. Guthrie recommends a 4-inch-thick woodchip mulch.

Growers will need to water for most Minnesota summers. They need to fence around the area to keep out cottontail rabbits at the snow depth. A south and southwest shade barrier may be needed.

Vines tend to twist counterclockwise and may be trained to a trellis — a T-bar or pergola, a crossbeam with an open lattice. Backyard growers can use chain-link fence. Newly planted vines take four or five years to train.

One of the challenges is pruning.

Major pruning is in mid- to late autumn, after plants attain dormancy. Allow pruned areas to dry out over the winter and reduce sap flow or bleeding. In late winter, pruning cuts lead to bleeding, so Guthrie advises pruning sites be painted with latex paint.

In spring and early summer, growers typically shear or shape, thin and train. Starches stored in the woody tissue of the vine canopy are converted to sugar. They translocate to the roots in the fall as day length shortens and nights become cool. Guthrie advises no pruning from mid-July until fall.

Berries have a limited shelf life because of small size and high sugar content. They have a relatively high surface area to mass, so require humid storing conditions so they don’t dry out.

American resurgence

Italy is now the world’s largest kiwifruit producer, with up to 240 frost-free days. Italy supplies the fruit within that country and surrounding European destinations.

New Zealand is the world’s biggest exporter and houses many of the crop’s scientists. There are specialists on everything about the kiwi — root architecture, molecular biology, breeding, storage disorders, nutrition management and other disciplines.

“Their brown, fuzzy kiwis are not the best-tasting kiwifruit,” Guthrie says of New Zealand’s production, “but they keep in storage up to eight months. That’s really what kicked off the kiwifruit industry.”

Guthrie is a generalist on the kiwi plant on behalf of Minnesotans.

“I wear a lot of different hats,” he says, noting that he pays his own way to travel to international research events that are held every four years around the world.

Today, USDA studies kiwifruit in Corvallis, Ore., and at the University of California-Davis. Auburn and Cornell universities are among the other leaders. California has the nation’s largest acreage, most in the central valley, by Sun Pacific Marketing Cooperative Inc., of Los Angeles. Guthrie says the largest single cold-hardy acreage probably is about 100 acres at Hurst’s Berry Farm in Sheridan, Ore.

“In California, one of the problems is windbreaks — the cost of taking them out,” he says.

Besides overseeing the kiwifruit work in Minnesota, Guthrie maintains a large collection of about a dozen species at his home and puts in seedlings from many crosses.

“I’ve been able to identify certain plants with very desirable characteristics, for the backyard gardener, for the commercial scale,” he says, noting he has a checklist of desirable traits. Not all kiwifruit types have the same number of chromosomes, so there is a challenge.

Guthrie is optimistic about how the kiwifruit will expand in the region. Most of the cold-hardiness will reside with the female, so we take the more cold-hardy plant and use the female of the two species and the pollen from the noncold hardy plant

“We’re making some crosses now where the potential for improvement is great,” he says. “Who knows? We may have the ‘Honey Crisp apple’ of the kiwifruit.”