The most pleasing chore I have had in the yard over the past few weeks has been making sure that branches don’t break under the weight of their fruit. This certainly hasn’t been needed on all of my fruit trees, but there are some this year that would be torn apart if I didn’t intervene and thin the crop. What a chore that isn’t a chore!

And making sure that trees aren’t damaged is the only reason that I ever remove fruit.

Thin fruit to increase size?

I know that some people thin fruit with a different goal in mind — specifically, to attain bigger fruit.

This has long been the tradition. “The one chance for the home gardener to get bigger and better fruit than he can buy is in the thinning process,” reads the original 1954 edition of the Sunset Western Garden Book.

How is this said to work? “A tree’s leaves supply energy for growth; if there are not enough leaves on the tree to support the number of fruit that set, the fruit will, in effect, compete with each other for carbohydrates and so remain small,” explains Chuck Ingels in The Home Orchard.

And so you can even find ratios for how many leaves a tree needs in order to grow a single fruit to its maximum size. “On average, twenty-five to forty leaves produce the green nutrition to support a growing fruit,” writes Michael Phillips in The Holistic Orchard.

Methods of thinning fruit

From here, we are offered different methods for thinning a tree’s crop in an efficient and effective manner. We can count leaves, but this is time consuming. We can take an estimate of the tree size and then estimate how many pieces of fruit that tree can develop to full size. For example, in the book Peaches, Plums, and Nectarines: “In California, early season peaches and nectarines are thinned to anywhere from 300 to 900 fruit per mature tree, depending [on various factors].”

But the thinning method that is easiest to follow is based on fruit spacing. Ingels in The Home Orchard: space peaches and nectarines 5 to 7 inches apart on a branch; space plums 4 to 6 inches apart; and space apricots 3 to 5 inches apart.

Kevin Hauser, in his book Growing Apples in the City, suggests removing all but one apple per cluster (there’s usually five) and spacing each fruit at least 8 inches apart. Similar spacings are usually recommended for pears.

(The practice of thinning fruit is most common on peaches, nectarines, and apples; and then it’s also often advised for plums, apricots, and pears too.)

The theoretical explanation to support the idea that thinning fruit will “allow each remaining fruit to develop to its maximum size” (The Home Orchard) makes perfect sense to me, but does it work in practice? What I’ve observed in my own trees and the trees of others leaves me unsure.

Fewer fruit means bigger fruit?

I’ve been thinking a lot about the practice of thinning fruit over the past month, and I’ve jotted down dozens of examples of trees that do and don’t have bigger fruit when they have fewer fruit. I won’t list them all here. I’ll mention a few that incorporate trees of different kinds, and I’ll suggest possible explanations for what they show.

I’ll start with the example of my Royal Blenheim apricot tree because I actually wrote a post about thinning its fruit a few years ago: “Don’t thin apricot fruit in order to increase fruit size.” As the title makes obvious, I found no difference in fruit size between a year when I thinned the fruit a lot and a year when I didn’t.

One possible explanation for this is that I keep this tree pruned small (to the height of my reach).

My Royal Blenheim apricot tree.

Why would this matter? Pruning can be considered a form of fruit thinning; it’s just that the fruit was “thinned” before it was ever allowed to appear in the first place.

However, when you prune a tree you cut off branches that would also have leaves, and those leaves would be photosynthesizing and able to support the growth of fruit. So I’m unconvinced that this explanation captures what is going on with my apricot, at least not in full.

Variety largely determines fruit size?

Variety might determine the size of fruit more than crop load. Examples of this abound. My grandmother had a peach tree whose fruit she didn’t thin, and we found it with a main branch snapped under the weight of multitudes of large peaches. I have a peach tree whose fruit is always tiny no matter how many pieces of fruit I allow it to keep. It seems that these trees are destined to produce a certain size of fruit regardless of how much fruit they carry.

And I’ll add one more example just because it is extreme even though it does not involve the typical deciduous fruit trees that are usually thinned. I have a Reed avocado tree that is about 12 feet tall, and because of last July’s heatwave, it dropped all of its fruit except one. That’s some extreme thinning.

How big is that single avocado fruit being powered by hundreds of leaves? Just normal size for the Reed variety.

Climate influences fruit size

When a particular fruit tree grows in a climate it finds suitable, it seems to produce bigger fruit no matter how much fruit it has in a given year. I often visit friends and family in the Pacific Northwest, and when I do I take note of domesticated and feral fruit trees alike. The apple trees up there are always mobbed with fruit — way more crowded than spacing guidelines recommend — and yet the fruit is often large.

My son, wishing he lived in Corvallis, where the sidewalks are paved with apples.

The apples on my trees in Southern California, on the other hand, are often on the small side — even though I keep the crop loads down in comparison to the trees up north. Other apple trees I know in Southern California likewise usually have fruit on the small side. (One exception is my grandmother’s Beverly Hills variety apple tree.)

My sense is that climate is the main factor influencing fruit size here. Apples love to grow, and grow big, in Oregon and Washington in comparison to Southern California.

So do pears. Here is a Bosc pear tree I found growing on the grounds of Rogue Farms in Independence, Oregon that is breaking all the thinning rules and yet has fruit as big as any Bosc pears I’ve ever seen.

They tasted great too.

Other factors influencing fruit size

There are many factors that influence the size of the fruit on a tree, some of them certainly still unknown to me. All of the authors and resources that I quoted above do make mention of factors other than thinning that influence fruit size. In fact, Peaches, Plums, and Nectarines adds that lack of required winter chill can cause smaller fruit, as can extreme summer heat.

Yet, the practice of thinning a tree’s fruit quantity is treated in most of these resources as having the potential to significantly alter the size of individual fruit remaining on a tree, and I just don’t see it. Of the trees I know, the correlation between low fruit quantity and large fruit size is inconsistent at best.

My reason for thinning fruit

Therefore, if I remove fruit from my trees I do so with a different aim: to maintain the health of the tree.

Burgundy plum fruit needing thinning
Branch broken because of not thinning fruit. (But note that Burgundy plum fruit was still full size.)

I’ve broken branches because I didn’t thin enough, and I’ve sunburned branches and fruit for the same reason. (See my post “Oh, the mistakes I’ve made: Not thinning enough fruit on a plum tree.”) I’m determined not to do that again.

This pencil-sized branch might snap under the weight of this load of Flavor King pluots as they grow.

How I thin fruit

Here is, briefly, how I go about thinning fruit in order to ensure that trees aren’t damaged. I look for branches that are hanging down from the weight of fruit and appear to have the potential to either break or be exposed to sunburn. Branches whose bark is not shaded by leaves and which are horizontal or facing south or west are especially prone to sunburn. I remove as much fruit as necessary on those branches.

Apples and pears are easiest to thin using pruners.
On thin branches, leaving more than one apple at the tip is just too heavy. The branch will get sunburned as it bends horizontal.

This goes for the deciduous fruit trees that we typically thin, but it also goes for evergreens like citrus, avocado, and mango.

Which fruit to thin

I first look to remove fruit that is imperfect, if possible: scarred, very small, deformed, doubled, spurred. I also look to remove fruit near the tip of a branch more than at its base because fruit at the tip has more leverage and causes more hanging.

Cluster of nectarines at end of branch. I’d remove that scarred one first.

Thin in rounds

But I am not a courageous fruit thinner so I never get the job done in one episode. I thin fruit in rounds.

The first round happens whenever the fruit is at a size where little to no fruit will continue to drop naturally. If you try to thin fruit when it’s only pea size, then you’re thinning some fruit that the tree wasn’t going to keep anyway. Wait a few more weeks and you’ll see that some fruitlets turn yellow or shrivel or stop growing or just seem to disappear; they were not completely pollinated or something else caused the abcission.

Now it’s easy to tell that those two fruits are going to drop naturally anyway. No need to thin them.

When peaches, nectarines, plums, apricots, pluots, apples, and pears are between marble and golfball size, and they look healthy, then they are probably set for life. If you want to remove some of them, then at that size you can be sure you’re dealing with the tree’s real crop load.

I always later end up noticing branches that remain too heavy and have to do second or third passes through a tree to thin a little more.

The upshot of my couple rounds of thinning fruit for the health of the tree is that, ironically, I end up leaving only a bit more fruit on my trees than traditionally recommended. So in a sense, the main practical difference between my approach and thinning with the aim of attaining large fruit is what’s in the mind of the thinner. The total number of fruit remaining on the tree is not always significantly different.

I’m not alone!

Nevertheless, I was glad that I confessed my suspicions about the effect of thinning on fruit size to a group of fruit-tree enthusiasts last week. At a meeting of the North San Diego County chapter of the California Rare Fruit Growers, I asked if anyone else had not noticed fruit growing bigger on trees with thinned crops, and some said they had.

That made me feel less crazy. And to boot, someone at the meeting mentioned that she actually preferred small fruit anyway.

I do too! I said.

We agreed that we didn’t understand the appeal of an apple that is so big that you have to refrigerate half of it for later. But what does that have to do with thinning?

You might also like to read my post:

Growing fruit trees in Southern California

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