Thinning Fruit for Tree Health
Southwest Yard & Garden
by Marisa Thompson
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).
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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.
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. For videos on fruit thinning, visit https://nmsudesertblooms.blogspot.com/2018/05/through-thick-and-thin-managing-fruit.html
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 the 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.
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.
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