Thinning Fruit for Tree Health

These two branches from the same peach tree at the NMSU Agricultural Science Center at Los Lunas on May 29, 2-18 had noticeably different peach sizes (photo credit M. Thompson)

Question:

My peach tree branches are hanging lower as the peaches get bigger. Is it too late to thin the fruit?

- Savannah M., Alamogordo, NM

Answer:

The good news is that you have fruit this year! Late freezes, gusty winds, and hail storms have taken their toll on the crop load this spring. It snowed in Farmington on May 21st. A friend with an organic farm in Mora said a freeze on May 31st caught them off guard. I’ll be surprised if we get 10 lb of peaches from our 88 peach trees this year at the NMSU Agricultural Science Center at Los Lunas. Last year we were in peach heaven, so I planned ahead this year to host multiple peach freezer jam workshops with Valencia County Cooperative Extension Family and Consumer Sciences Agent Laura Bittner. We had to cancel our plans when I saw the pitiful fruit load.

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)

Last year I wrote about the benefits of fruit thinning and the hazards of not paying attention to how laden your branches are. That column is reprinted below.

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 makeshift 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.

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.

These twin cherries at the NMSU Agricultural Science Center at Los Lunas on May 29, 2018 didn’t need thinning—they were perfect (photo credit M. Thompson)

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.

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.

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.

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)

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

Links:

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook page.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!