The why of fruit thinning

I noticed one of the apples in the food forest had finished blooming and now had tons of tiny apples clustered on its branches. I took the situation in hand and started to pick them off.

13217562 - close up of bee pollinating apple blossom
photo by Jenella

Five flowers form on each spur, leaving five small fruits after pollination. They naturally fall off, one by one, until a single fruit is left to make seed. Contrary to what we might think, an apple has grown to its maximum potential within thirty days after the flower drops its petals. From this point, any ‘growth’ is just cells filling up with sap like balloons. The number of balloons to be filled with juice resulting from cell division is already decided.

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I was pulling off all but one fruit on each spur. From this, I expected each apple left on the tree would have more nourishment from the tree, be larger, and better shaped. If I had waited for the tree to pair down the fruits itself, it would have divided that nourishment between all those extra apples that would never stay on the tree anyway.

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Is there a drawback to this unnatural thinning? Perhaps.

When plucking off the fruits I noticed a few had codling moth damage. I have gotten fine harvests of apples from my trees, with very little, if any, codling moth damaged in years past. Whether this is an especially good year for codling moth population or not might explain this damage. Or perhaps the tree had dropped much of the fruit with codling moth damage so I never noticed? It quickly occurred to me the tree grows the extra fruit in part to increase the chances at least one will make seed -as codling moths eat the seeds of the apples they infest.

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Codling moths have several generations through a season, so we will see if the moths come back for more later.

Another effect of thinning apples is more regular fruiting. The seeds in each fruit create a hormone that blocks fruiting the next year. Some varieties of apple are notorious for their violent fruiting cycles -one year not a fruit on the tree, the next (or year after that) the branches break for the myriad fruit clogging the works. By thinning, a moderate amount of hormone is produced every year, allowing a moderate amount of fruit every year.

Perhaps such staggered fruit production in un-thinned apples is a tactic for cutting down on codling moth population?

As is, thinning delivers better results for me. But my trees are also quite small -just barely above my head. Thinning falls into what I call pleasurable interaction with the food forest, or work I enjoy, and usually only takes five minutes or so to complete.

I may quit it in years to come, and just trade thinning time and larger fruit for hacking out the good hunks from myriad smaller fruits. Masanobu Fukuoka, when his students asked how they could grow good apples without equipment and sprays, said to simply feed the poor quality fruit the students thought eminent to pigs. I’m not so skeptical as Fukuoka’s students; I have seen my trees produce quite healthy fruit already, so we’ll see what they give as the system builds. Below are some of my Fuji apples last year.

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You may wonder how the heck massive orchards ever thin their fruit one by one. By machine? No, by chemicals. Hormones in trees largely dictate the quality and growth of the fruit. We have developed an array of synthetic hormones, of which there are no counterparts in nature, that cause apple trees to drop their fruit. Run some experiments to properly calibrate the dosage, and you have thinned trees by simply spraying. Some of the hormones they have developed even increase the cell proliferation process beyond what the fruit tree offers, resulting in abnormally large fruit. I’ll let you research the health effects of these synthetic hormones.

When I first came across this information years ago, I went on a long search for an equivalent that could be derived from plants. I didn’t come across one, or any information on a hormone pathway that could cause the fruit to drop, accept for stressing a tree, or simply reducing pollination. I am suspicious there is an even more elegant answer:

I find that increasing the health of trees and their ecology in general can can at times truly transform their character. Mortal Tree is still a long ways from being notably fertile. But Fruiting factors are building on their own in some places. So perhaps the good effects will get out of hand, and produce some good results I never would have expected. 

 

9 thoughts on “The why of fruit thinning”

    1. Thanks Anni for your interest in this subject. I regret I don’t have a more clear cut suggestion for action; but perhaps someone else in seeing this might have an answer of which I’m not aware. I look forward to more updates on your trees. How is the dwarfing going?

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      1. Hi Luke, so far so good with the trees, apart from losing one this winter and nearly losing another last year. I may have selected varieties that don’t like Wales in these cases! I will be doing a post about the trees a bit later in the year.

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          1. Yes, I guess relative to the continental extremes in the US and Europe our climate, being maritime, is milder. I haven’t checked yet, but I think the tree that has died originates from France and maybe needed different conditions. Or, my other theory is that the very dry spring made a crucial difference and it just dried out.

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  1. I haven’t thinned my apples so far. It seems my dessert apple tree is very good at not overburdening itself, although of course this could change over time (I also suspect it is to do with pollination).

    However, at the farm where I do voluntary work they had branches coming off a tree because they were too full of apples – we’d missed this tree when we were thinning the apples.

    Anyway, interesting information. I hope you will get a good crop without too much codling moth damage.

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    1. Glad to hear my observations correlate with yours. Some varieties really are much better at parsing out their fruiting each year, so perhaps your dessert apple won’t ever need much attention unless for encouraging larger fruit. Thanks for mentioning it. >

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  2. I have two remaining Apple trees, one died. One of the remaining trees had no blossoms this year. The other was loaded with blossoms. I have not done any thinning, but observed that the Sugar Crisp tree must have self pollinated, as there were no other apple trees nearby. The fruiting spurs had many blossoms on each spur. It appears that most of the blossoms dropped off due to lack of pollination. I see one or two fruit developing on each spur.
    I did spray some fruit tree spray in hopes of heading off coddling moths. So far, I see no sign of any damage by insects. This young tree is 3 or 4 years old. this year is the first year it bloomed, and at last count there are at least 18 apples hanging on. I’m not sure if I should thin these down to 10 or 12 fruit all together, or should I just wait to see how the tree handles itself!
    Advice will be appreciated. GOD bless!

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    1. You would likely get the best results if you thinned the fruit to just one per spur. It is a bit late in most climates to get much effect from thinning, because the fruits have already developed for the most part. But it is worth a try. 3 or 4 years old should in most cases be adequate for fruiting if the tree is healthy. That the other one isn’t blooming means it’s either happy and growing rather than fruiting, or unhealthy to the point it can’t fruit. Sometimes heavily fruiting can be caused by stress, so it’s hard for me to tell. Interesting how it was pollinated without any surrounding pollinator. Thanks for mentioning.
      What do you have around the trees? You might look at my post The rules of spacing,* if you haven’t already, for some info on how to make trees healthy. Feel free to ask any more questions you like under that post, or here if this hasn’t fully answered you. Your question is much appreciated. God’s blessings on you as well.

      *You can view it here: https://mortaltree.blog/2017/02/24/the-rules-of-spacing/

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