To prune, not prune, or how much to prune is one of the most debatable issues among California’s almond producers.

While full pruning is a century old tradition, the latest research from pruning trials in California, including those at the Nickels Soil Laboratory in Arbuckle, are bending the debate minimal pruning.

“Despite what some people are saying, the University of California has never said don’t prune almond trees,” said almond researcher John Edstrom who manages the 200-acre, privately held Nickels Lab. He also serves as the University of California, Davis (UC Davis) farm advisor in Colusa County.

“Research results suggest that growers should minimally prune trees and be very judicious and conservative about it. Only remove limbs that are bad offenders or problematic,” he said.

Edstrom said research showing only minimal pruning is necessary hasn’t changed everyone and perhaps it shouldn’t because there are differences in soil and varieties. What it boils down to is tree vigor - how quickly trees grow under different conditions across the state.

The first of two almond pruning trials at Nichols began in the early 1980s. Edstrom was at the helm of each. The initial testing was on trees in fairly weak soil on a single hose drip, low vigor conditions. Results showed no yield reduction for trees left unpruned for 22 years compared to conventionally pruned trees.

“That was really an eye opener,” said Edstrom. “It initiated discussion among growers, consultants, and farm advisors. Plans were initiated to start a second trial under more vigorous conditions and more advanced growing techniques.” It was begun in 1997.

Findings confirmed

A decade later, round two confirms the initial findings. Minimum pruning yields about the same nuts. UC Davis Glenn County Farm Advisor Bill Krueger was also a leader in the second testing round.

Edstrom reported on the second trial findings during the Almond Industry Conference in Modesto, Calif., in December.

“How long do we need have to run these trials to be sure that we have enough information to make it advisable to avoid pruning in the younger years leading up to year 10,” he asked. “For now growers should experiment with very low pruned blocks to see how it fits their production condition.” Another 10 years of the second study should tell the true story, Edstrom added.

Backing up the results at Nickels are pruning studies by UC Davis’ Kern County Farm Advisor Mario Viveros and Stanislaus County Farm Advisor Roger Duncan. Those trials also basically resulted in no significant yield loss with minimum pruning.

Edstrom said, “Each trial in general has shown the same thing – yields were just as much on minimally pruned trees and perhaps getting a higher yield on 10th year trees compared to conventional pruning.”

The million-dollar question is why? Why do minimally pruned trees yield about the same as the traditional approach?

It’s related to current tree sizes and the lifespan of modern orchards.

“The reason why the lack of pruning makes sense today is we are producing smaller trees that don’t stay in the orchard long enough for the shading phenomena to develop far enough to make a big difference,” he stated.

Old orchard spacing was 30 by 30 feet compared to today’s spacing of 16 by 22 feet and even closer. In addition, orchards are removed earlier so the end result is minimum pruning to succeed, Edstrom said.

email: cblake@farmpress.com