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Photo, this page: Early variety peach trees at Enns Packing were mechanically topped after harvest (around the second week of June) and then topped again around the first week of September. Short trees still require dormant pruning.

Photo, this page: Early variety peach trees at Enns Packing were mechanically topped after harvest (around the second week of June) and then topped again around the first week of September. Short trees still require dormant pruning.

Excitement in California’s stone fruit industry often centers on hot new varieties of peaches, plums, or nectarines. One of the latest trends creating interest is about growing shorter trees.

Short trees are catching on as California stone fruit growers look for ways to reduce their labor costs. Orchardists are training new trees as well as retrofitting older trees to the shorter heights. However, growing shorter trees involves much more than just whacking off the tops.

Different spacing, training, and light management are among some of the considerations that go with lowering tree height without using dwarfing rootstocks. And though California growers are still on a learning curve, even some traditional orchardists are becoming believers in the new system.

Tall trees have been the standard in California’s peach, nectarine, and plum orchards for more than a century, according to Kevin Day, University of California tree fruit farm advisor for Tulare County. Productive, fertile soils, abundant labor, and Nemaguard, a widely planted, vigorous rootstock resistant to nematodes, have encouraged the growth of large trees, some exceeding 13 feet tall.

Changing economics in the 1990s and today’s tight labor supply have forced growers to reevaluate all farming practices, especially regarding labor, an input that accounts for more than half of annual production costs in soft fruit.

Day began studying the economics of growing shorter trees in 1997, planting two- and four-leader trees at standard heights of 12 to 13 feet and reduced heights of 8 to 9 feet and tightening up the spacing from traditional orchard systems. Scaffold limbs on the shorter trees were tied down for wider, flatter trees. Later, his research expanded to six-leader hexagon-vase systems.

In an article reporting results of Day’s research previously published in the February 1, 2004, Good Fruit Grower, Day concluded that labor costs could be reduced from 10 to 45 percent, depending on the activity, in the short tree blocks when ladders were not used. The research also showed that when light interception is constant, short trees have as great a capacity to bear and size a crop as do tall trees.

Grower experience

Enns Packing in Dinuba, California, is one of many growers experimenting with shorter trees. Rod Riffel, farming operations manager, said they began looking at ways to reduce their labor costs five years ago, targeting tree height as one area. The family-run packing operation, established in the 1940s, grows, packs, and ships peaches, plums, nectarines, apricots, table grapes, and other specialty tree fruit.

Riffel said that by reducing their peach and nectarine tree heights by 20 percent—going from 12 to 10 feet—they have also reduced labor costs by about 20 percent. With labor costs averaging $2,400 per acre, a 20 percent reduction results in a savings of $480 per acre.

They first tried the new orchard system in a 20-acre block. The next year, they expanded the trial to 180 acres. “Some things are just so obvious,” he said, referring to the labor efficiencies gained in the short-tree blocks.

Data collected during 2006 showed that yields from the fifth-leaf short trees were close to full production, Riffel noted.

“The amount of fruiting wood hasn’t really changed in the two orchard styles (conventional and short), and they are producing about the same yields.”

Much of the labor savings is related to summer pruning chores, a task that can run $180 per acre for extensive summer pruning when using a ladder, Riffel said. Trees are mechanically topped at a cost of $35 per acre once or twice in the summer. After topping, workers can walk through the block with long shears to remove suckers. Ladders are not needed for summer pruning.

Ladders are used during dormant pruning when fruiting wood is selected and trees are cleaned up for the next season. “But pruning is faster because of the height reduction,” Riffel added.

Trees are trained to have five to six scaffolds in an open-vase system called a hexagon-vase or hex-V configuration. Branches must be tied down during the early years to develop wider, flatter branch angles. The flatter branches help suppress tree vigor.

One of the biggest challenges with the short trees is managing excessive vigor, Riffel noted. Growers must be careful not to overfertilize or overwater. Careful light management is also needed—too much canopy can shade fruitful buds, while too little can cause sunburn inside the tree.

“We’re still learning things,” he said, noting that they are working to further reduce tree height to nine feet and are experimenting with the timing of mechanical topping.

UC researchers are studying optimum dates and severity of mechanical topping, along with using water stress to help reduce tree height and control regrowth and tree vigor. Scientists are also assessing the effects of topping treatments on orchard light interception and tree regrowth the following year.

For decades, growers used mechanical topping to bring more light into the trees. Now, the radical technique is used as an inexpensive way to maintain a lower tree height.

Nonselective

Riffel recognizes that mechanical topping is a labor-saving tool, but he noted there are drawbacks to the practice.

“The trouble with topping is that it’s very nonselective,” he explained. “If it wasn’t for the labor issue, I’d never have the trees topped.”

Riffel said that timing of summer topping is influenced by vigor of the tree and timing of the crop—whether the variety is early or late. Thus far, they are maintaining tree height by topping twice in the summer, but they are still fine-tuning the practice as they search for the best timing.

Since Day’s initial short-tree research began, two new dwarfing and semidwarfing rootstocks for peaches and nectarines have been patented and released by the University of California. Other promising dwarfing rootstocks are also under study. Until the industry learns best horticultural practices for the new rootstocks, shorter trees on standard rootstocks offer growers a transitional step to reducing labor costs.