Post Harvest Pruning of Mature Orchards

Pruning is one of the subjects that can have ten people explain it in ten different ways. This has to do a lot with the traditional thoughts on how an almond tree should look, the believed benefits of pruning, and personal experiences. It is one of the most important practices of orchard maintenance due to the expense and its effect on orchard yield and longevity. Therefore pruning should be considered more of a science than an art.

Pruning can be broken down into two phases: The tree training phase and the maintenance period phase. During the tree training phase, we work to establish and shape the permanent framework of the tree through primary and secondary scaffold selection. This occurs through the first three years of the orchard life. The maintenance pruning phase occurs from the 4th leaf on and is done to maintain the shape of the tree. This post will focus on pruning during the maintenance period of the orchard life.

In order to understand the principles of pruning, we need to understand the underlying principle of orchard management: We are farming sunlight. The more sunlight that is intercepted by tree leaves, the more production we can achieve within our orchard. Therefore, trees need to fill the available space as quickly as possible to achieve maximum yields. Along with this, we want to ensure orchard viability by having sufficient fruitwood to produce a sizable crop for the life of the orchard.

So, to do this, do we need to prune?

The short answer is "no." Studies by by farm advisors Roger Duncan (Stanislaus Co.), John Edstrom (Colusa Co.), Bill Krueger (Glenn Co.), and Mario Viveros (Emeritus, Kern Co.) have demonstrated that pruning does not increase yield over minimally, or "unpruned" trees (Table 1). As we can see, conventional, annually pruned trees did not yield more than "unpruned" trees in the varieties planted. Furthermore, "unpruned" tree productivity did not appear to decreased through the 21 years of the longest trial performed.

Table 1: The comparison of cumulative yields from four varieties of conventional, annually pruned and "unpruned" almond trees from four research trials in California. (Note: Unpruned trees referred to trees in which branches were moved out of neccessity due to other orchard practices, i.e. spraying and shaking).

One main point to keep in mind in the above studies is the expense of orchard pruning. Even though annually pruned and "unpruned" pruned trees performed relatively equally, the amount of money made per acre is higher in unpruned blocks. Crews still need to go through "unpruned" orchards to remove diseased, dead, broken, and/or low branches, but this takes significantly less time than annual tree pruning.

What are the benefits of pruning?

The benefits of conventional pruning appear to be minimal. Cutting healthy limbs out of trees to maintain "shape" usually ends up decreasing fruit wood and yields. Making large cuts also open the tree up to infection by the tree pathogens Botryosphaeria, Ceratocystis, Eutypa, and Phytophthora - especially when done near a rain event.

What is meant by "unpruned"?

Growers should limit pruning to cutting away branches that need to be removed out of necessity. These reasons include:
- Equipment access (shakers, sprayers, etc.),
- Safety for the tractor driver,
- Reducing foliar diseases including Alternaria, Hull Rot, Rust, etc.,
- Removing Dead or diseased limbs from the orchard,
- Reducing sticks at harvest.

Only by knowing your orchard and its peculiarities will you know the proper amount of material to prune. The decision to prune should not be done just because of tradition or orchard looks, but because of the benefits that it can provide to the orchard and, most importantly, your checkbook.

For more information on pruning and spacing, please check out the following research reports and presentations:
"Almond Tree Pruning by the Numbers," By Roger Duncan, UCCE Stanislaus Co.
"Integration of Tree Spacing, Pruning, and Rootstock Selection for Efficient Almond Production," Project Leader: Roger Duncan UCCE Stanislaus Co.