Almond growers have traditionally pruned their trees, and the practice went unquestioned for many years. Perhaps it was a holdover from caring for fruit trees, says University of California Cooperative Extension farm adviser John Edstrom. After all, many of the state’s original almond growers started as peach growers, and the trees are closely related. However, many of the very good reasons for pruning peach trees simply don’t apply to almonds.
Peach growers prune their trees mainly to increase fruit size and improve color, neither of which apply to almonds. Edstrom has now been studying the issue for nearly a quarter of a century, and he’s convinced that when it comes to yield — the primary reason almond growers prune — there’s no advantage to pruning. The first pruning trial was planted at the Nickels Soils Lab in Colusa in 1979. Edstrom and his colleague Bill Krueger took over the trial in 1984, and at the time he too thought pruned trees would fare better. But not any more. “The yield was at least as high, and certainly no lower, in the minimally pruned trees,” he says. “It’s a shocking piece of data in almond culture.”
Many growers have remained skeptical, especially since the original trial was on a high-density (7 feet by 22 feet) hedgerow block with questionable soils. So in 1997 he planted a second trial to better reflect the state of the industry. It was planted in good soil with a more standard spacing of 16 feet by 22 feet and irrigated with microsprinklers. “It’s a nice, strong orchard by any standard,” he says. “And it too showed that minimally pruned trees yield at least as well as traditionally pruned trees.” (See chart.)
Minimal Vs. Unpruned
While many growers use the term “unpruned,” Edstrom is quick to note that’s not entirely true. After the first leaf, it’s important that an almond tree is pruned during dormant season. This pruning is mainly for limb training, he says. Three or four primary limbs are selected, and all competing limbs are removed to provide the tree with a sound structure. After that initial pruning, however, the trees are left alone. Edstrom adds that it’s not just the trials he and Krueger have performed that bear out his conclusion. His Cooperative Extension colleagues have conducted similar trials throughout California almond country, and have garnered similar results.
Edstrom understands why growers are skeptical; he himself once was. He thinks a lot of it stems from the fact that a pruned block of trees looks a lot cleaner and better-maintained than a block that hasn’t seen pruning shears in many years. “People will get embarrassed if their trees don’t look as good,” he says. “But it’s hard to argue with the facts.”
Yet another fact is that pruning obviously costs more than simply leaving the trees alone. In addition, growers who prune have to dispose of the clippings, says Edstrom. While in the past that wasn’t that big a deal because they could simply be burned, air quality regulations have been instituted in recent years that prohibit burning in many areas.
Take A Hard Look
Some growers still insist that they need to prune to let in light so the lower fruiting wood doesn’t get shaded out as the trees age. However, if that were a big concern, Edstrom thinks the minimally pruned trees in his original trial would have started yielding less than the pruned trees. He understands the concern, however, and will continue to monitor the trees carefully as they age. “How much light do we need to maintain? We really can’t say for sure,” he says. “But my hunch is that it’s really not going to turn out to be that big a deal.”
Edstrom emphasizes that he doesn’t want to be so presumptive as to simply tell growers not to prune. However, he’s heard many reasons for pruning, and most of them don’t hold up. According to Edstrom, growers shouldn’t prune just because:
- Your trees look better.
- Your labor contractor recommends you do it.
- The grower across the street does it.
- You’ve always done it.
Instead of looking at the issue from that angle, Edstrom suggests growers take the opposite approach. “You need a strong reason to make a pruning cut,” he says. “Think about it before you do it.”