The trick is to manage the tree so it produces that desirable nine- or 10-row cherry instead of smaller 11- or 12-row fruit, says Greg Lang, horticulture professor at Michigan State University.
High-density plantings used in combination with dwarfing rootstocks add up to more trees per acre than in a traditional cherry orchard, and thus mean a much higher potential yield per acre, Lang says. That's countered by the need to reduce crop load to match the smaller leaf area and gain fruit size.
"In a well-managed orchard, there should be roughly equal yields," whatever the rootstock, he says.
Matching rootstocks with variety selections plays a big role, Long says. Precocious varieties such as Sweetheart, Lapins or Skeena require more management when matched with a precocious rootstock such as Gisela 6.
Gisela 6 produces trees not much smaller than Mazzard, but the semi-dwarfing rootstock responds better to hard pruning, making it easier to keep under control, he says.
In tests, the Sweetheart-Gisela 6 combination produced packouts with 76 percent of the fruit at 9 1/2-row or larger.
Mazzard may have produced slightly more of the large Sweetheart cherries, but over time the Gisela trees won out in total yields.
"The returns were probably greater over time with Gisela over the Mazzard," Long says. "And that's with the most difficult (rootstock-scion) combination."
While Tieton fared poorly in evaluations on Mazzard rootstock, it shined when combined with a dwarfing rootstock, Whiting says.
'No combination is necessarily better'
But, he cautions, "No combination is necessarily better. Some may require a little more management or a little less."
Other rootstock options include Gisela 3, 5 and 12, Edabriz, Weiroot 158 and 72, Krymsk 5 and 6, and an Oregon rootstock bred from Mazzard and Mahaleb dubbed Maxima 14.
Learn new management approaches
To ensure fruit size, growers must learn new management approaches, Whiting says.
You can't prune a tree on Gisela rootstock as if it were a Mazzard tree, he says. Instead, he recommends plenty of heading cuts and limiting shoot growth to remove future fruit sites.
At the same time, growers should plant trees closer together and prune aggressively. Leaving more space and allowing the trees to grow vigorously to fill in the gaps only produces more fruit sites and leads to a large crop of small fruit, he says.
Deficit irrigation is another way to control vigor, but not one Lang recommends. "I'd rather work with the tree instead of fighting its natural tendencies," he says.