Through Thick and Thin: Managing Fruit Load on Backyard Trees

Southwest Yard & Garden by Dr. Marisa Thompson
~30 second demo video of peach fruit thinning with Valencia County Extension Master Gardener, Carol Bennefield in Bosque Farms on May 27, 2018.  
~45 second video explaining how we started thinning a peach tree in Bosque Farms.


Question:
Several branches on my peach tree are hanging lower and lower as the peaches get bigger. Is this OK or should I be thinning the fruit?
-     Carol B., Los Lunas, NM
Answer:
On the one hand, you don’t want to thin your peach tree too soon and then lose the fruit you saved to a late frost or the dreaded hail storm. On the other hand, reducing the fruit load on heavily bearing branches has major benefits.
First of all, the branches you’re describing that are hanging lower as the peaches develop are in danger of breaking. If the weight of the fruit just bends the branch, a strong gust of wind can be the final straw. And “breaking” is a kind word. Often, it’s more of a terrible rip-like tear that can damage the main trunk irreparably.
Pruning back longer branches earlier in the year, ideally when the trees are still dormant, can help with overall structure and improve the tree’s ability to handle a larger fruit load without breaking. But here it is, practically summertime, and decisions need to be made now.
Sometimes longer branches hang so low they touch the ground before breaking. And I’ve seen people prop up laden limbs with make-shift crutches. However, brutal branch breakage isn’t the only reason for fruit tree thinning. By harvest time, each peach is a storage tank for the sugars (aka carbohydrates) that were produced in the leaves during photosynthesis. This process requires sufficient leaf surface area for enough sugars to be made to support each individual fruit and make it maximally sweet.
These two branches from the same peach tree at the NMSU Agricultural Science Center at Los Lunas on May 29 have noticeably different peach sizes (photo credit M. Thompson).

Have you heard that you should remove all fruit in the first years after planting to encourage healthy root establishment and better harvest in the future? [long sigh] Me too. The brutal truth is that photosynthesis is limited when your tree has very few leaves. When the canopy is small in the first few years or when the tree has been stressed and lost leaves, it makes sense to remove most or all of the fruit load so that the newly generated sugars can be spent on root establishment and stronger woody tissues rather than the fruit. The plus side is that developing healthy roots, trunk, and branches increases the chances of longevity and better yields in the years to come.
What about apple trees, cherries, apricots, or pears? The thinning strategies generally apply to all of them. Some species and cultivars produce clusters with more flowers than others, so there is some variation. Apple trees are especially known for heavy fruit set and the need for thinning. Research on apples has shown that optimal fruit size and yield is possible when the leaf-to-fruit ratio is approximately 30 leaves per apple, depending on the cultivar and associated leaf size. And cherries may not need thinning as much as other fruits. As fruits ripen, the benefits of thinning dwindle.
Clusters of cherries this red may be too ripe to get the full advantages of thinning, especially with such an abundant leaf canopy (photo credit M. Thompson).
These twin cherries at the NMSU Agricultural Science Center at Los Lunas on May 29 don't need thinning—they're already perfect (photo credit M. Thompson).

Depending on how far along your trees are by now in the season, you may already see that some of the smaller, damaged fruit are shriveled and fall easily when you barely touch them. That’s nature thinning the fruit for you, and it’s commonly called “June drop”—even if it happened in May. Moments after you finish reading this column, you’re going to generate your own “June drop” by selecting the smaller, damaged, uglier fruits in each cluster and twisting them gently but firmly until they fall off in your hands. It really is that simple. Drooping branches are the ones that need it the most and are easiest to reach, so go ahead and thin those right now.
These two fuzzy fruitlets in Lordsburg at the Hidalgo County Extension Office on May 30 would have been good picks for thinning if they didn't fall off first (photo credit M. Thompson)

In any tight fruit cluster, there’s an additional reason for thinning. The spot where two fruit press together often gets mushy and rotten, plus pests like to get in there and make a mess. Recommended spacing between thinned fruits varies, but a simple rule of thumb is to create a space 2–3 times the size of a mature fruit; that way they won’t touch. Rules of thumb are made to be broken, so set the spacing guideline aside when you see obviously damaged, puny runts.
Here’s one final tip for new growers: Ask friends to thin the fruit on your trees and offer to do the same for theirs because it can be emotionally debilitating to rip the tiny precious fruits from your own tree.

BONUS VIDEO! I pulled this cast pupal skin of a carpenter worm out of a Navajo willow trunk in Bosque Farms on May 27, 2018: 

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the NM Desert Blooms Facebook page (@NMDesertBlooms)
Please copy your County Extension Agent (http://aces.nmsu.edu/county/) and indicate your county of residence when you submit your question!

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms (http://desertblooms.nmsu.edu/) and the NMSU Horticulture Publications page at http://aces.nmsu.edu/pubs/_h/.

Marisa Y. Thompson, Ph.D., is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505- 865-7340, ext. 113.

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