The tall spindle orchard design that is being so steadfastly encouraged by researchers—and adopted by growers—in the eastern United States came about from the discovery of several important principles.
In the 30 years he has been working to develop the tall spindle system, Cornell University’s Dr. Terence Robinson said he was guided by five principles:
1. Studies on light interception showed that the highest yields required that trees intercept 70 to 75 percent of the light. Growers who wanted pedestrian orchards of around eight feet tall couldn’t achieve that unless they went to very narrow alleys that are too narrow for current machinery. That meant trees need to be taller, about 12 feet, and the alley width about 90 percent of that.
2. Studies on light distribution showed that thick canopies have too much heavily shaded area which results in poor quality fruit. “This has led the effort to narrow the canopy of modern orchards to not more than three feet deep (four to six feet from side to side),” he said.
3. The need for early high yield to pay back the initial orchard investment led to studies on how to improve early yield. This resulted in the use of feathered trees, higher tree densities, irrigation and fertigation to maximize early tree growth, minimal pruning (especially not heading the leader), and branch bending to induce early cropping.
4. Simple and thin tree canopies are more adaptable to mechanization, and the tall spindle design made it easier to use platforms to improve labor efficiency. The process of renewal pruning also reduced labor cost by simplifying and speeding up the pruning process.
5. Tree density is subject to the law of diminishing returns. At some point the cost of additional trees is greater than the yield gain. Cornell economic studies put this number at around 1,000 trees per acre with tree costs around $7 each, but above 2,000 trees when tree cost is $2 a tree.