Growing high-density cherries
Research shows that tree density is a key to growing cherries profitably in the eastern United States.
This slender spindle orchard system produced high yields early in the orchard’s life because of minimal early pruning.
There are many challenges to growing sweet cherries in the eastern United States, but several horticultural advances, including high-density plantings, dwarfing rootstocks, and new varieties, are encouraging more growers to consider sweet cherries.
Problems like high tree mortality, bacterial canker, low yields, big trees, and rain cracking face cherry growers in the East, said Dr. Terence Robinson, horticulturist at Cornell University’s agricultural experiment station in Geneva, New York. “All of these problems together have discouraged a lot of growers from producing sweet cherries. But as apple prices have declined in recent years, there is more interest now in diversifying to cherries.”
Robinson sees many opportunities for eastern U.S. sweet cherry producers, many who grow fruit for U-pick or farmers’ markets. “There seems to be endless demand for high-quality sweet cherries,” he said during the Great Lakes Fruit, Vegetable, and Farm Market Expo in Michigan. He pointed to advances made in managing dwarfing rootstocks and high-density plantings as opportunities to improve the productivity and profitability of cherry production.
Additionally, his research has shown that rain covers or diversion nets can help prevent cracking, one of the biggest problems facing eastern sweet cherry growers.
Robinson draws his conclusions from five- and eight-year trials in New York comparing cherry rootstocks, varieties, and six different orchard systems—steep or central leader, Spanish bush, Vogel slender spindle, perpendicular V-trellis, Marchant angled trellis, and Zahn vertical axis. The rootstocks are Gisela 5, 6, and 12, with Mazzard and MxM2 (Mazzard and Mahaleb hybrid) as controls.
His research shows a strong relationship between tree density and yield and gross returns over the first seven years. Yields from high-density plantings can be substantially higher than the yields of traditional orchards.
Rootstocks had a large influence on cropping in the first seven years of the trial, Robinson said. The dwarfing Gisela trees were up to five times as productive as trees on seedling stocks, with G.5 more productive than G.6 or G.12. Among the six orchard systems tested, the highest cumulative yield was with the vertical axis system, followed by the slender spindle.
He pointed out that with such large crops on the dwarfing rootstocks, crop load management with pruning or thinning will likely be necessary to achieve large fruit size.
Results suggest that modern cherry orchards in eastern states should have tree densities ranging from 300 to 800 per acre to achieve high early yields. U-pick orchards should have 300 to 500 trees per acre, he noted. Higher densities of 400 to 800 trees per acre should be used with G.5, intermediate densities (300-500 trees) with G.6, and lower densities of around 300 trees with G.12, the largest of the three Gisela rootstocks.
In evaluating the impact of tree density on gross returns to the grower, Robinson found that dwarfing rootstocks dramatically improved the bottom line. The large differences in yield resulted in more than a threefold difference in cumulative crop value between the vertical axis system and the low-density central leader system.
“For MxM2 rootstock, you gain an additional $21 for each additional tree that you plant,” he said. “But for Gisela rootstock, it’s $81 to $87 more money per additional tree you plant. I know that Gisela trees are more expensive to buy, but over eight years, you will make $70 more per tree. It seems like a reasonable investment and is probably worth every penny to buy the more expensive rootstock.
“That’s why I’m so excited and enthused about these rootstocks,” he added.
Robinson found that the training systems that use minimal pruning during the early years—such as vertical axis and slender spindle—have higher yields. The vertical axis, planted with six feet between trees and nearly 500 trees per acre, has been the most profitable system during the eight years. Trees are around 12 to 13 feet tall, but there are no big branches as they are always cut out.
Training systems that rely on extensive pruning during the first four years, such as the Spanish bush, central leader, V-slender spindle, and Marchant trellis, have low yields in the first five years. As the trees mature, systems that use aggressive pruning (Spanish bush, central leader, and Marchant trellis) are more likely to produce large fruit size with Gisela rootstocks.
“Certain varieties, like Regina and Lapins, get fairly good fruit size without lots of special treatment,” said Robinson, adding that specific pruning and crop load management may be needed to get large fruit size on G.5.
He believes that tree size can be contained by planting trees closer together. However, if short trees are desired, aggressive pruning will still be required. Also, he didn’t observe as great differences in fruit size due to the orchard system as he originally thought there might be.
Early training can be difficult if minimal pruning is used because, for most cherry varieties, there is insufficient lateral branching if heading cuts are not made. He suggests special branching techniques that don’t rely on heading cuts during the first four years, like bud removal or a combination of scoring plus Promalin.
Feathered trees are needed for the vertical axis and slender spindle system, Robinson said.
He is enthused about results in the five-year trial of Regina, a sweet cherry variety from Germany. Compared to Lapins, Regina, a late-season, crack-resistant cherry, showed a dramatic increase in yields on G.5, as well as size differences on all rootstocks compared to Lapins.
Regina fruit averaged 11 grams in weight, while Hedelfinger, Lapins, and Sweetheart averaged from seven to nine grams per fruit. For farm markets in New York, nine grams for fruit size is acceptable, Robinson said, though six grams would be considered too small.
“Here you have a beautiful, big cherry,” he said of Regina. “It may be the salvation of the sweet cherry industry in New York. We’ve had yields of Regina unheard of in New York, and not just big yields but also big fruit size.”