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Do fruits need to be thinned on the tree? For example, I have a young Pomelo tree that's producing fruit for the first time. In order to get bigger, nicer fruit, should I be thinning the fruit? How is it done?

Here's a good example cluster from my Pomegranate tree:

Pomegranate cluster

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3 Answers

up vote 12 down vote accepted

What is "thinning"

Thinning simply refers to the process of removing fruit from the tree when it is still small (or not fully ripened). Some fruit trees require more thinning than others. For e.g., it is common to talk about thinning peaches/apples/apricots, but not cherries. While "how much to thin" might depend on the type of fruit tree, the reasons for thinning and the benefits are general.

Why should you thin?

Fruit trees usually produce way more fruit than they can handle. Depending on how the pruning was done, the exact amount can vary, but in general, they do. Just as with everything else in nature, fruits on a tree compete with each other for essential nutrients and space. This can become a problem with young trees that are

  1. not strong enough to support the weight of the fruits and
  2. not big enough to provide nutrition to all the fruits.

While these are the primary reasons for thinning, there are other benefits to it.

Benefits of thinning

  1. Once you thin the fruits, the remaining fruits have more space to grow, so you get bigger fruits.
  2. More space leads to more air circulation and sunlight, which in turn leads to better fruit flavor and color.
  3. A common reason for fruit rot on the tree is because the fruits are touching each other closely. The decay occurs where they touch, because the skin couldn't breathe. Thinning reduces the chances of this occurring.
  4. Less chance of damage to the tree (My <1 yr old peach tree almost broke in two because it was burdened with 7 enormous peaches and I did not know about thinning back then. Also I did not expect a tree this young to bear fruit! Luckily the gophers did it for me.)
  5. Since the tree can now support the smaller number of fruits, it is not overburdened with supplying nutrition to the fruits.
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I'm sure the answer depends on the fruit type and the particular tree. In the case of peaches, I've heard it suggested that you should thin every other fruit so that the remaining fruit grow large. Total weight produced is unaffected, but the peaches are more of a practical size to eat. The reason I know this is because I have a small peach tree. We had two blossoms (!) for the first time, so hopefully next year we'll have more blossoms, some fruit, and I can try the advice!

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In a word, yes, thinning is good. It will happen naturally as fruits fall victim to insects, wind, or animals, but you can do it early to raise the quality on average.

In apples (the other pom fruit) you get a "king blossom" in the center of a cluster which is first to open and likely first to be pollinated. You can tell because it drops its stamens first (which your photo seems to show.) To be really sure of pollination, wait til the fruit ovary (behind the blossom) swells to marble size. You can thin the others in the cluster by pinching the stems or twisting the ovaries off.

I have never seen a pomegranate tree (zone 4/5 is home) but I read they have similar clusters of 1-7 blossoms. You will need to find out how many fruit is a fair number for your size tree, or what spacing is appropriate, and thin to that amount. In a young tree, removing all the fruit may be rational if you prefer more rapid growth.

On an apple tree it is acceptable to thin to one fruit per cluster. I didn't take this seriously enough when my total fruit set was poor this year, and I kept two hopeful fruits per cluster. In the end I got more small and medium fruits. Smaller fruits (especially with insect damage) are harder to use unless you have a grinder and juice press.

I've read one study that found slightly higher total mass from thinned crops. Logically, the outcome is limited by leaf area so I think they must have meant higher economic yield, or else were not counting windfalls. For sure, thinning increases the percentage of quality, saleable fruit.

Commercially, thinning is done with carbaryl spray which is a vasoconstrictor, but you probably don't want to do that (though you can easily buy Sevin) and it has different potency against each variety. Chemical thinning is done when the king ovary passes marble size because its stem is thick enough to withstand constriction. But Honeycrisp for example can lose 100% of its stems and must be thinned manually.

Number of fruit this year also influences how many fruit buds are set for the following season. So if you have a pom fruit that bears heavily, you can get into a cycle of on year, off year. It's better for the tree's growth to have steady production.

If you'd like technical explanations of these things, one bulletin online is "CHEMICAL FRUIT THINNING OF APPLES" from the Geneva station. Much of it is applicable to manual thinning too.

Finally, my experience is with apples, not pomegranates or peaches, so I'll be eager to learn how each varies.

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