Dominant side branches are not an issue in these Honeycrisp knip trees because the central leader dominance is well established. (Melissa Hansen/Good Fruit Grower)
Knipboom trees require a different mindset from orchardists who are used to planting standard, one-year nursery trees, says a Washington State horticulturist. But planting the bigger knip trees may be a cost-effective way to quickly fill in orchard space with less training and pruning than what is traditionally required.
A knip block of Gala apples, planted in 2007, “didn’t do much” the first year, said Dale Goldy, horticulturist for Washington’s Stemilt Growers, Inc. Goldy is also a partner in Gold Crown Nursery in Quincy, Washington, with Andy Gale and Dave Piepel.
The knip trees only grew about four inches in 2007, though they were seven feet tall when planted.
“The first year, you’re basically keeping them alive,” Goldy said of the 30-acre Ultima Gala orchard. But in 2008—the second year—the block produced 3.5 bins per acre, a number he admits could have been higher if they’d known more about what they were doing.
“The instantaneous orchard concept is new to us,” he said, remarking that in hindsight they should have pruned more branches off the trees in the first year to better maintain the central leader dominance.
Lack of first-year growth of knip trees has been the hardest thing to understand, he said. “Though they didn’t grow the way you wanted in the first year, they’re still bigger than what you would have with second-leaf bench grafts.”
More importantly, growers must change their mindset and focus their efforts on the parts of the tree they can’t see. Knip trees have well-feathered tops, he said, explaining that the root-to-top ratio must be brought into balance after transplanting from the nursery. “Drip irrigation and fertigation in the first year are huge in getting the trees quickly back in balance.”
With just a few years’ experience of growing knip trees, Goldy said they are still at the bottom of the learning curve. Because knip trees are relatively new to U.S. growers, Goldy has had to travel to Italy to learn about knip tree production and growing techniques. “The closest place to see knip tree in nurseries is 18 hours away,” he said, adding that it makes learning more difficult.
Their start into the knip system was serendipitous. Stemilt Growers’s retired president Tom Mathison ordered bench-grafted, one-year-old Pinova trees from a local nursery for a new block he was planting in Quincy. The small size of the one-year bench-grafted trees made everyone wonder how they would fill space in the orchard. The decision was made to leave the trees in the nursery, cut the tops off the following spring, and make knip trees out of them the second year.
“When the Pinova trees were planted, we all commented, ‘Wow, now that’s a tree,'” Goldy said. While the trees didn’t grow much the first year, they grew well in the second leaf, and even had a small crop.
Pinova is a German-bred cultivar also called Corail. Piñata is the trademark of the fruit produced by Stemilt.
One of the biggest challenges to the knip system is that growers will have fruit in the orchard much earlier than they would normally expect.
“You have to treat knips as bearing trees from the start and manage your crop load,” he emphasized. “You need to make sure you don’t overcrop too early before the tree reaches the top trellis wire.”
Growers must also be prepared to install trellis and irrigation systems as soon as knip trees are planted. “When you plant a knip tree, the trellis has got to be there once it leafs out,” he stressed. “Every day, the leaves and top are getting bigger and creating that much more tree to be whipped around by the wind.”
But Goldy noted that there are also challenges when growing standard trees, such as filling orchard space. For example, in a Honeycrisp block planted in the spring of 2008, the one-year trees showed good growth by fall. However, in the coming year, they must decide whether to crop the trees or fill the space. “The risk of not filling space with Honeycrisp—a variety that wants to produce fruit—is that it’s very hard to make it up later,” he said.
Knip trees also are more challenging for the nursery to grow. There is more risk involved in growing a two-year-old tree than one with a shorter turnaround time.
Knip trees may be beneficial in organic apple production. At Gold Crown, they are growing Fuji on Pajam2 rootstock destined for an organic apple block. “Our goal is to have the trees as big as we can in the nursery before moving them to the organic block,” Goldy said, noting that a bigger tree should allow the grower to transition the conventionally grown nursery trees to organic faster. “If we can plant trees that are seven feet tall, hopefully we wouldn’t have to push them as hard to get the trees to reach the trellis at ten feet.”
From a financial standpoint, knip trees are more expensive and cost about $1 more than standard trees. But Goldy points out that knip trees put fruit production closer to when money is being spent on things like trellis and irrigation installation, tree training, fumigation, planting, and such. “You’re shortening that time between when you spend money and when it starts coming in.”
Several more years of experience in growing knip trees are needed before he can give cost comparisons between standard and knip trees. But already, he thinks knip trees will have lower tree training costs than standard trees. There may be some initial limb tying and pruning needed in the first year or so, but after that, minimal training and pruning should be required.
Melissa Hansen is the research program director for the Washington Wine Commission. Hansen previously was an associate editor at Good Fruit Grower from 1996 through 2015.
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