Pruning Almond Trees

Pruning recommendations vary by the farmer, consultant, and even the University researcher. Some advise to prune trees hard to regenerate growth (not so much in CA anymore), some suggest that only a few limbs be removed annually, while others advocate throwing away the pruning shears. With these differences in opinion, what is the proper way to prune a tree?Young Orchards:Research has shown that reduced pruning on younger trees can lead to larger, earlier yields. This is mostly due to increased canopy that is able to produce crop. Some research has found early benefits of leaving young trees unpruned, but have found that over time, these branches will split when the crop load begins to increase leading to yield loss. Hence, some structuring of first and second leaf trees is recommended to address tight branch angles and close proximity of scaffolds, which leads to included wood and weak branches.Scaffold selection on young trees should be based on growing conditions. There is no set number that is ideal, and a farm level decision should take into account tree vigor, spacing and management practices. Heading the trees higher at planting (42” or higher) will provide more opportunity to select scaffolds, but will increase pruning time. Heading the trees too short may lead to issues with shaker head placement at maturity, leading to more bark damage. After the first year of growth, select scaffolds with distance in between and avoid scaffolds on the same plane and height of the trunk of the tree. By spacing the scaffolds vertically and around the tree, the growing limbs will be better attached, leading to less breakage. Remove steep angled limbs as these are often weaker. Limbs with a 45-60 degree angle are ideal. Avoid hard heading cuts as cutting the tree back too hard can spur lanky, vertical regrowth the following spring. My experience has shown that cutting trees back to a wood diameter of ½” to ¾” diameter generally provides the desired growth response. Finally, remember that less vigorous varieties and trees will require less pruning than more vigorous trees.After the selection of scaffolds in the first year, not much pruning is needed. Typically, 1-2 cuts per tree is needed after the second growing season to remove limbs that are vertical or crossing over the tree. Limbs that are too low and are in the path of orchard operations should also be removed. After the third growing season, pruning should focus on removing limbs in the way of operations.Mature Orchards:Mature tree pruning should be minimized but not neglected as maintenance pruning does need to occur. Typically, maintenance pruning is performed as thinning cuts to remove limbs that are in the way of operations or to help develop the desired architecture of the tree. Keep in mind, however, the results of multiple research trials that have shown no yield benefit from pruning mature trees. These long term studies from Kern, Colusa, and Stanislaus Counties have found no yield differences within mature orchards. There are, however, reasons to prune mature trees, including:  easier access, worker safety, increasing the amount of light to the orchard floor to assist with drying, and to remove broken, dead, and diseased limbs. Another reason that is often not discussed is to reduce pest and disease pressure. UCCE research out of the Sacramento Valley has shown a 6% decrease in navel orangeworm infestation in the upper canopy in pruned trees due to better insecticide spray distribution in the upper canopy.Hedging- or making indiscriminate heading cuts in the upper canopy - mature orchards generally isn’t recommended. Even though this operation is useful for increasing the light on the orchard floor, it often leads to large sections of the productive canopy being removed. These heading cuts also create an odd regrowth pattern in which new limbs grow vertically. Instead, consider selected limb removal by making thinning cuts to help increase light penetration. This type of maintenance pruning may not be needed every year, allowing for the cost to be distributed over a three to four year period.Pruning should only occur when rain is not in the forecast to avoid wound infections by pathogenic  fungi  that  disperse spores during rain events. This is especially true with young, developing trees. Wounds can be susceptible up to two weeks after pruning, with larger wounds taking the longest to heal.  Even with this healing time, pruning paints are not recommended as they can slow the healing process. Ongoing tests with biological agents have shown some promise, but they are still under evaluation. Pruning as late as leaf out will have no impact on tree growth.