Almond Tree Pruning

Mario Viveros

UCCE Farm Advisor, Kern County

Deciduous Tree Fruits and Nuts

September 29, 1999

Almond harvest has been unusually slow this year due to the cool and humid weather. The next cultural practice in an almond orchard is pruning which is not weather dependent but requires skill and knowledge of tree growth and development.
Books define pruning as the art and science of removing unwanted limbs from a tree. Since books don't elaborate on it, I can offer the following interpretation. The art of pruning is the ability to create an eye- pleasing tree canopy utilizing the natural growth habit of the tree. The science of pruning is the ability to utilize research-based information to create an everlasting productive canopy. Some people may not see the relationship between the art and the science in pruning, however, both interrelate with each other in the principals of pruning. Let's discuss some of the pruning principles which are used in almonds.
Tree Balance. A well-balanced tree is symmetrical, pleasing to eye, tolerant to wind damage and productive for many years. A well-balanced tree is made up of a perpendicular trunk and three or four well-placed scaffolds around the trunk of the tree. The grower can balance a tree with pruning cuts. Two common causes for an unbalanced tree are the prevailing wind and sunlight on the south side of the canopy. If the prevailing wind is pushing the canopy into the center of the tree, prune limbs from the inside of the canopy. This will allow outside limbs to develop into the wind. If the canopy is leaning toward the south due to the action of the sun, thin out limbs from the south and outside of the canopy. This will allow limbs from the south to grow upright.
Stiffening Cuts. These are heading cuts by which one-third of a limb or a shoot is removed by the pruner. This cut is done when the limb or the shoot is too limber. This cut is especially beneficial to stiffen main limbs during the training of young trees. Keep in mind that during the training years, you want the tree to grow upright toward the sky. Also, stiffening cuts will result into a strong canopy where future crops will be born.
Light Management. The main principal of pruning is light management. In young trees we want light to cascade down to the main scaffolds. This will stimulate the creation of fruiting positions on secondary shoot growth. In older trees, it will maintain productive wood in the lower half of the tree. Light penetration through the canopy is achieved by thinning cuts. Crossing-over and parallel limbs should be eliminated. Keep in mind that two parallel or two crossing-over limbs are occupying the same space. The inside of the tree should be kept reasonably open by eliminating water sprouts and limbs growing through the center. A common mistake is to eliminate the lower limbs and leave the upper problem limbs. This will not only eliminate productive limbs but also will force the tree to grow higher into the sky. This may not be desirable for mature trees. You can evaluate your pruning by the amount of sunlight you see cascading down the tree or by the amount of sky you see through the tree's canopy.
Crop Management. In the past, I have stated that pruning can be used to reduce alternate bearing in almonds - prune heavy in a light crop year and prune light in a heavy crop year. Experience has taught me that this principle may not be applicable to all orchards. If a grower has problems with yields, he needs to evaluate other cultural practices that might be more limiting than pruning. One cultural practice that limits yields is post harvest water stress. If a grower has this problem, he needs to overcome it before he considers pruning.
Tree Size Control. The best method to control tree size is with a big crop. Nut set effectively reduces vegetative growth, therefore reducing tree height. One can increase nut set by tipping (heading cuts) horizontal lower secondary branches on fourth- and fifth-leaf trees. This type of pruning cut will stiffen horizontal branches, promote fruiting position behind the cut, and reduce the vegetative response to a pruning cut.
Tree size control in mature trees can be achieved with tower pruners. This machines reduces tree height by selectively cutting back the tallest branches. The reduction of tree height has significantly reduced navel orangeworm reject levels. Topping and hedging for tree size control has been successful in young almond trees (fifth- and sixth-leaf trees) but they have not been successful in ten- to twelve-year-old orchards. The yield reduction in older orchards makes this practice unacceptable.
Pruning is a very popular orchard activity among almond growers. Growers tend to prune because the neighbor is pruning and not because the trees need any pruning. Before you prune your trees, examine the reason for pruning and what you want to accomplish from this expensive cultural practice.