Neither; but too much pruning will result in the tree dropping more fruit, because it cannot support it.

Well, that seems to say #2 is correct.

On a macro level, that may be correct; but in the specific case of one fruit on the tree the growth of that fruit will not be affected. If you had a number of fruits, the tree would likely drop some, resulting in fewer fruits. Physiologically, the energy for the fruit growth comes mostly from the roots; and the energy from the limbs and leaves serves to replenish the roots and later to provide more growth.

It would increase the amount of N and water from the roots for everything remaining on the branch. Likely make the fruit bigger and more watery. That is, if you left about 30 leaves or more upstream. Fruit can't create much of its own energy. Physiologically, almost all of the energy comes from the leaves for the growth of the entire tree, wood roots and fruit, as I understand it- the roots send up no sugar. Maybe John knows something I don't, though. I'm no botanist. I don't think roots send stored carbohydrates upstream.

I thought it was the opposite as well? Doesent the energy for fruit growth come from the leaves fed from the roots and the roots replenish the energy to the leaves? I thought roots only use the nutrients and water to help the leaves provide the energy/sugar to grow/fruit? I could be wrong.

On a side not, I have read that the number of leaves needed per fruit is anywhere from 30-50.

I'm not clear here. Are you folks saying that the leaves past the last fruit on the branch (from the last fruit to the branch tip) do provide energy for all the fruit. If so, pruning the leaves off would seem to provide less energy to the fruit, resulting in smaller and/or worse fruit. Correct?

I don't think anyone can precisely answer that question but leaves closest to any given fruit provide most of the sugar and energy for cell enlargement and division (increase) of that fruit. 30 to 40 leaves are said to be capable of producing all of this the fruit needs so more leaves further upstream than this will probably not benefit the fruit. If leaves further up shade light from leaves closer to the fruit they could reduce the quality of said fruit.

I've always read that energy for the fruit comes from the roots (at least in peaches) up to the pit hardening stage. After that the fruit gets it's carbohydrates from the leaves.

Below is an article I've linked before, but provides a little more detail to my statement above.

I agree completely that fruits absorb carbohydrates from local foliage. For larger fruits 30-40 leaves. For cherries 2 only leaves are required.

As an interesting aside, I've also read that leaves have to be ahead of the peach/fruit for it to benefit from the leaves. While I think this is generally true, I've seen many peaches grow on little shoots that only have a little tuft of 2 or 3leaves at the end of the small shoot (These peaches should have been removed.)

These peaches are certainly smaller than other peaches, but interestingly if they are left on the tree for a long time they generally end up with an acceptable flavor.

I've also seen some peaches at the very end of the shoot with no leaves past them. They too are smaller, but also generally end up with a decent flavor.

Because of this it's my theory peaches can absorb some carbohydrates from foliage downstream, even though the literature says otherwise.

Here is a link that might be useful: How to grow big peaches

So, it seems that summer pruning should leave sufficient number of leaves upstream and not prune back to right after the last fruit. That's very helpful. Thanks all who posted.

Olpea, somehow the idea that carbohydrates are delivered to shoots and fruit from the roots has never penetrated my own brain in spite of a couple years in hort school and an awful lot of subsequent reading. I was under the impression that it was stored in nearby wood. I will now try to search out the known facts in the matter.

I should add that fruit quality is generally enhanced by partial girdling of fruit plants. Perhaps this is accomplished by only stopping the downstream flow without interfering the upstream flow from the roots which I assume is what scoring and other partial girdling techniques accomplish.

OK, I spent as much time as I'm going to this morning and from what I've read the question of carbohydrate contribution to fruit development is largely theoretical but for some fruit plants there is strong evidence that the roots do deliver carbohydrate to fruit in its earliest development.

This is based on the drastic reduction of root carbohydrate reserves in the earliest stages of fruit development, although it is not currently possible to actually track the flow of the missing carbohydrate. There seems to be a lot of variability on this and it seems to depend on the sequence of fruit to leaf development.

If the fruit gains a lot of size before there is much leaf development than it relies more on the photosynthate it produces from its own tissue and from stored carbohydrate from other parts of the tree including the roots. As soon as leaves are developed enough (and are receiving adequate light and warmth) to produce adequate energy the tree stops depending on its reserves.

Thanks Hman,

That's also how I understand it.

If the PhD, fruit physiologist from Texas A&M Citrus research center can be believed... and I for one believe him... the primary impetus for fruit creation and development comes from nutrients sent up from the roots; later, as the fruit developes, the carbohydrates produced by the leaves and the stored carbos in limbs and trunk make a larger contribution; that is a whole lot more than I know; it is only what I learn from a lot smarter people than I. BTW, what I know is only about citrus; other fruits could be different.

Yeah be careful because they are serious about their stone fruits...hehehe;-)

I was to understand "girdling" as the process of cutting around and into the bark of a certain branch? This would work on only current year fruit production correct? Every year after the girdled wood would have to be cut for new growth? Im a little leery on the girdle method but I would like to try in on a couple branches of my peach trees.

Nothing I could find suggested that the primary source of photosynthates came from the roots only but that the roots contributed along with earliest leaves and the fruit itself. Maybe someone would like to search further.

I would be surprised that this is true of citrus as the research I saw showed a correlation of dependency on roots to how much leaf there was on the tree at the time of early fruit development, but nature is surprising. I'm pretty sure there is great variability on this from species to species and in the case of genetically divergent species like apples, variety to variety.

Anyone want to delve in further? I will probably wait until my work slows to expand my search.

Thank you Olpea, for once again informing me of something about fruit that I was unaware of.

it all about the time of pruning:
pruning to late in summer will have negative effect on size and sugar...
pruning to early will not effect size or sugar but it will increase regrowth the same year and will increase flower set the next year...