How to Determine Optimal Almond Tree Spacing

Almond trees should be spaced at a distance that will provide the ability to capture 80% to 85% of the sunlight at maturity. (Photo Credit: David Doll)

Having a successful almond orchard starts with determining orchard density. Identifying the ideal distance between trees and rows should maximize the canopy development and sunlight capture of the orchard without impacting long-term productivity. The ideal spacing is site specific, but is essential in determining establishment costs, site modification, and the general look of the operation.

Tree density is a component of the distance between trees and aisle width. As the distances between rows and trees decrease, orchard tree density increases. Increasing orchard density impacts tree growth and orchard yield. Young almond trees grown in similar conditions generally yield a similar number of nuts per tree.

Tree density is a component of the distance between trees and aisle width. As the distances between rows and trees decrease, orchard tree density increases. Increasing orchard density impacts tree growth and orchard yield. Young almond trees grown in similar conditions generally yield a similar number of nuts per tree.

This means that increasing density will increase young orchard yields and suggests that almond plantings should be as dense as possible. This appears to be true, but recent research and field observations suggest that there may be a point of diminishing returns in orchard density.

This means that increasing density will increase young orchard yields and suggests that almond plantings should be as dense as possible. This appears to be true, but recent research and field observations suggest that there may be a point of diminishing returns in orchard density.

As a densely planted orchard matures, the trees’ canopies begin to grow together, reducing sunlight within the lower canopy, which decreases lower fruiting wood. These closed canopies often have higher humidity, which increases diseases. Furthermore, decreased aisle width makes equipment access hard, leading to increased tree damage.

As a densely planted orchard matures, the trees’ canopies begin to grow together, reducing sunlight within the lower canopy, which decreases lower fruiting wood. These closed canopies often have higher humidity, which increases diseases. Furthermore, decreased aisle width makes equipment access hard, leading to increased tree damage.

Growers often choose to hedge or prune these canopies to reduce these problems which increase operational expenses and reduce orchard yields. This creates the question: What is the proper orchard density?

Definitive Trial
A trial established in 2001 by Roger Duncan, University of California Cooperative Extension in Stanislaus County, has provided the most insights into the impacts of tree spacing on almond tree growth. In this study, he planted ‘Carmel’ and ‘Nonpareil’ on either ‘Hansen 536’ or ‘Nemaguard’ rootstock and planted the trees as 10-by-22 feet, 14-by-22 feet, 18-by-22 feet, or 22-by-22 feet.

After 17 years, the trial has shown that decreasing the distance between trees will decrease tree size, which leads to a reduction in tree loss and shaker damage. This is thought to improve orchard longevity since tree loss is reduced, and if a tree does die, a smaller amount of total orchard canopy is lost.

Trial results varied by rootstock and variety, in which smaller trees, e.g. ‘Carmel’ on ‘Nemaguard,’ had a higher cumulative yield from the tighter spacings of 10-by-22 feet or 14-by-22 feet while larger, more vigorous trees, e.g. ‘Nonpareil’ on ‘Hansen 536,’ had a higher cumulative yield when spaced farther apart, 14-by-22 feet to 18-by-22 feet. This suggests that spacing vigorous trees too tightly can reduce yield.

There is not a similar study that tests varying aisle spacings. Most operations within California plant between 21 feet to 22 feet, with some orchards as close as 20 feet and wide as 24 feet. These spacings tend to be set based on operational preference and attempt to balance disease, equipment access, and other concerns.

Observations from a local orchard operation that planted different aisle spacings suggests that placing rows too close together negatively impacts tree production by increasing the need for pruning to provide equipment access. Ideally, tree aisle width should be far enough apart to allow equipment access and for trees to grow, but close enough that it can capture around 80% to 85% of the sunlight.

When designing the orchard, the distances between aisles and trees should be considered together. Planting trees closer together down the tree row may reduce tree size, which could mean that the aisle width should be adjusted. This, however, is just one of many points to consider.

The decision should also include the cost of increasing row density, the varieties and rootstocks selected for planting, expected orchard vigor, anticipated cultural practices, and risk of inclement weather at harvest. Each one of these are outlined in further detail on the next page.

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