Lynn Long, Oregon State University Extension educator, gives a pruning demonstration during an international tree fruit meeting held last winter in Boston.
The days of a moderate-sized cherry crop in the Pacific Northwest are gone, short of widespread weather events that reduce the crop. With more than 50,000 acres of sweet cherries planted in Washington and Oregon, last year’s record-setting crop of 23.2 million 20-pound boxes will be more common as young orchards planted to high density come into full production.
“We’ve got a lot of cherries planted,” said Lynn Long, Oregon State University Extension educator for Wasco County. “Nowadays, when we have a moderate- to large-sized crop, we have difficulty selling all of the fruit. We don’t need more cherries on the market. What we need are high quality cherries for the market.”
The way to produce large fruit, he said, is to prune to eliminate small fruit on the tree. “Pruning is by far the most important thing a grower can do to produce large, high quality cherries. Whether trees are on full-size or dwarfing rootstock, with today’s market conditions, there’s just no point in growing small cherries.”
Long offered the following pointers to help growers produce large fruit:
1 Prune out small and pendant wood.
This is especially important with Gisela rootstocks, but also with trees on Mazzard, Long said. “How many times have you seen pendant wood in a Mazzard tree where there’s no new growth at the end of the branch? Let’s get rid of that wood that will produce 11.5- and 12-row fruit and focus on growing the 9-row fruit.”
2 Keep the leaf-to-fruit ratio in balance.
The leaf-to-fruit ratio is important with all rootstocks, but is especially critical with productive rootstocks. He recommends having at least six leaves for every fruit on the tree. For productive rootstocks, that means tipping every branch to remove the mass of fruit that in two years will grow on the end of the branch. Fruit left on the end of the branch, particularly with Sweetheart and Lapins, usually grow in such tight clusters that they are misshapen and damaged when picked. Tipping the branches also stimulates new growth throughout the tree, helping keep the leaf-to-fruit ratio in balance.
3 Prune for light.
Light needs to reach all parts of the tree, not just the top of the tree. The industry has largely moved away from the top-heavy, vase-shaped training systems that allowed little light to reach the base of the tree.
“You want to have a pyramid or Christmas-tree shape to your trees to ensure that the bottom of the trees receive light,” Long said. “Make sure the top of the tree doesn’t dominate, especially if you’re using a central or steep leader system.”
Modern training systems, such as the UFO (upright fruiting offshoot), spindle, steep leader, and central leader, should treat each lateral branch as a temporary one that is rotated out for new fruiting wood. He advised growers to avoid allowing big wood on the top by pruning out or stubbing back laterals that are greater than half the size of the branch they emanate from.
4 Provide nutrients to achieve two feet of new growth annually.
“In order to grow quality cherries, you’ve got to have new growth on the tree every year, regardless of rootstock,” he said, adding there should be 18 to 24 inches of new growth throughout the entire tree. Growth is needed to maintain the leaf-to-fruit ratio and to supply carbohydrates for two years before the buds turn into spurs. Growers should test their soil every three to five years, using the nutrient levels as a baseline to show soil nutrient trends. If annual tree growth is less than desired, more frequent soil testing is recommended. Some growers also take annual foliar samples in August to show nutrition trends. Long encouraged growers to look at the total picture—annual growth, nutrient trends, and visual observations—when deciding on nutrient amendments. Relying only on one component, such as foliar sampling, can be misleading if you had a big crop or a lot of growth because the test will likely show low levels of nitrogen and other nutrients, he added.
5 Irrigate when the crop needs it.
Many growers in the Northwest overirrigate in the spring and underirrigate as harvest approaches.
“I see this happen time after time,” Long said, adding that overirrigation early in the season needlessly cools down the soil and discourages cell growth and division at a time things need to be happening. Later in the season, when temperatures are warm and trees are supporting a full canopy, growers often don’t apply enough water. Soil moisture can be determined through a simple touch-and-feel method (making a ball from soil collected a foot deep) or from a variety of soil moisture sensors. The important thing is that soil moisture is routinely measured. He suggests assigning a person or hiring a consultant to make sure the task gets done throughout the season. “If soil moisture levels aren’t read on a regular basis, they’re not very useful.”