Although growers are sometimes tempted to pick Juliet when they are bright red, the cherries are not ripe until the color deepens to the rich merlot hue shown here. Photo courtesy of the University of Saskatchewan Fruit Program.
The University of Saskatchewan (U of S) Fruit Program is breeding a series of dwarf tart cherries that are well suited for mechanical harvesting and U-pick operations. (Courtesy of the University of Saskatchewan Fruit Program.

About 200 miles beyond the northern border of Montana, fruit experts have been working on something unique: a collection of bush-type tart cherries that produce large, tasty fruits well-suited for mechanical harvesting. Canadians use the term sour rather than tart, but “in reality, ours are more tart and Americans’ are more sour,” said Bob Bors, head of the University of Saskatchewan (U of S) Fruit Program, including its Dwarf Sour Cherry Breeding Program.

“These varieties represent a breakthrough in having a bush cherry instead of a tree,” said Bors, who spoke at the 2017 Great Lakes Fruit, Vegetable, and Farm Market EXPO held in December. “And they can be renewed, because if you have old trunks, you can just lop them off when they’re seven, eight years old, and new ones will take over. You can keep the same bushes growing for a long time … probably the rest of your life,” he said, adding that this kind of renewal also keeps the trunks flexible enough for over-the-row harvesters.

Unexpectedly “amazing”

When Bors first joined U of S in 1999, which is the same year the university released its first dwarf sour cherry called Carmine Jewel, he didn’t appreciate just how unusual these dwarf cherries were. That changed when he presented data on the new variety at an international fruit conference in the northwestern United States.

Bob Bors
Bob Bors

“It was only my second year in Saskatchewan, and I came from a background of strawberries and raspberries, not tree fruits and certainly not cherries. I thought I was being brave doing this presentation on our cherries, because I figured they’d all tell me what I’m doing wrong,” he recalled. “So, I get up there, and I say the cherries are this big and the bushes are this big, and we think we can harvest them over these two weeks every year, and strangely, nobody asks me any tough questions.”

His first inkling that the cherries were something special came when the next speaker, a breeder from Finland, began his talk by acknowledging that his program’s sour cherries weren’t as big or as sweet as the Saskatchewan sour cherries. And that wasn’t all. “Then a guy from Hungary leans over to me and says, ‘Your cherries are amazing. They’re going to be what they talk about at this conference.’ And I thought to myself, ‘Oh my God!’”

Boosted by the unexpected and overwhelmingly positive reception at the conference, Bors and his group kicked the program into high gear. “We started devoting a lot of time to researching the cherries, figuring out how to propagate them in tissue culture, and looking at them more closely in terms of mechanical harvesting,” he said. The latter was of interest because the region’s short season didn’t draw immigrant labor, so growers were already exploring machine harvesting for Saskatoon berries.

The bush league

By 2004, the university had released five more cherry varieties in what it calls its Romance series: Romeo, Juliet, Valentine, Cupid and Crimson Passion. All are dwarf, high-yielding, hardy, bush-type trees. “I would say the best ones in the Romance series for flavor and prettiness are Romeo and Juliet,” Bors says. Both Romeo and Juliet are dark, wine-colored cherries that are excellent for fresh eating or processing. Valentine has a more traditional bright red color, just a shade darker than Montmorency. “This is our best for drying because of its color, whereas Romeo and Juliet may taste great dried but would look like black raisins, and the consumer might equate that with low quality,” he said.

Cupid tends to bloom five days later than the other U of S varieties, but Bors said it has two drawbacks. First, it takes an extra year to come into production. Second, the cherries are overly large. “In some years, half of the cherries will be too big for the pitting machine,” he said.

Crimson Passion produces a high-quality, very firm fruit, but he considers it “too dwarf.” He estimates the mass of the bush as about a third of the other U of S varieties. “We’ve also had trouble rooting it, and it’s slow to establish in the field, so I wouldn’t recommend those for a commercial grower.”

The breeding program’s initial release, Carmine Jewel, is a dependable, dark red cherry that has consistently highly production – typically 25 to 30 pounds per bush — and ripens earlier than the other varieties. This dark red cherry is not as large as those in the Romance series, but it has a high flesh-to-pit ratio and small pits.

Finding a niche

Michigan State University researchers have tested three U of S cherry varieties — Romeo, Juliet and Crimson Passion — since 2011 to determine how the dwarf varieties stack up against the Montmorency trees, which are typically grown on a standard rootstock and grow into tall trees.

“Because our harvesting systems actually clamp onto the tree and shake it, we have to wait until Montmorency is physically big enough, and that means that after we put them in, we don’t harvest until year six or seven. What we were hoping was that these bush-like trees would come into bearing sooner so we could come in with these new shaker harvester systems that can get fruit off these little bushes,” said Nikki Rothwell, coordinator of MSU’s Northwest Michigan Horticulture Research Center.

That study demonstrated that the dwarf cherries can indeed be harvested two or three years earlier with an over-the-row modified blueberry harvester.

The dwarf cherries don’t have much disease pressure up in Saskatchewan, although growers have recently begun to spray for brown rot, which has emerged due to increasingly rainy weather over the past five years, Bors said. The MSU study evaluated the same three varieties for susceptibility to cherry leaf spot and found they were no better against the disease than were Montmorency.

Rothwell believes the U of S varieties are a good choice, particularly for growers with U-pick operations. “There are different populations within Michigan who like that tart cherry, as well as eastern Europeans who have embraced tart cherries, so there are people who really want to come out and pick their own cherries,” she said. “With Montmorency cherries, you’d have to put people on ladders and that means liability, so there’s been some definite interest in these dwarf cherries in the U-pick community.”

The next project for the U of S Dwarf Sour Cherry Breeding Program is a new Musketeer series of fruit that is being developed with European markets in mind, Bors said. “There’s one called d’Artagnan that is designed for a certain type of sideways harvester used in Europe for black currants and by Saskatoon berry growers in Canada. The branches on that variety tend to stay small, thin and flexible for a long time, so it will go a decade before its branches need pruning.” No release date is available yet.

The U of S fruit program is also developing other fruits, including haskaps/honeyberries, apples, hazelnuts and grapes, but the dwarf cherries remain a highlight. Details about the University of Saskatchewan’s six dwarf tart cherry varieties are available at •

The secret life of Saskatchewan’s dwarf tarts

As director of the Dominion of Canada’s Forestry Farm in Saskatoon, Saskatchewan, Les Kerr’s primary job was to develop ornamental and disease-free trees and shrubs to be used as bird habitat and wind breaks. But in 1944, Les Kerr got sidetracked by cherries.

“He was supposed to be working on shelterbelt trees and not edible fruits, but he had crossed Mongolian sour cherries (Prunus fruticosa) to some northern varieties, and to hide his breeding program from the government, he would have farmers who were growing his shelterbelt plants also grow his cherry seedlings,” said Bob Bors, head of the U of S fruit program.

He would visit his trees, select the cream of the crop and cross-pollinate them. Presumably, he continued working with breeding these after his retirement in 1965, but the project remained a secret.

By 1983, Kerr’s clandestine work had led to some interesting cherries, but his health was failing and his program was in jeopardy of being lost forever. “He was dying in the hospital when one of his nursery friends (George Krahn) told him he should inform the university about his secret cherry program,” Bors said. Kerr agreed. He met with University of Saskatchewan fruit expert Cecil Stushnoff, mapped out which farms had his best material, and bequeathed the trees to the university. Kerr died about two weeks later.

Stushnoff and U of S technician Rick Sawatzky picked up where Kerr left off and began crossing his trees to northern European and Minnesota varieties, most of which were obtained from the Vineland Research Station in Ontario. That work yielded the 1999 release of the U of S’s first dwarf tart cherry cultivar, a cold-hardy dwarf cherry called SK Carmine Jewel. Since then, the university has released five others and is continuing to develop new varieties.

—by Leslie Mertz