My Fruit Tree Pruning Observations and Theory: What Are Your Thoughts?

Hi all,
I have been a lurker for a while, but I don't post much. I am still fairly new to permaculture, but I am steadily picking things up.

Anyway, I wanted to hear thoughts on an observation/theory I have. I have long been baffled by pruning fruit trees. It seems like the trees know what they are doing, so why would they need our help? I have looked around for answers as to why pruning is so essential (as every mainstream source confidently asserts that it is). I find a lot of articles on how to prune, but almost nothing on why to prune! There is often a sentence or two that says something along the lines of "pruning helps keep your tree healthy and maximizes productivity." That seems counter intuitive to me (though that doesn't necessarily mean that it is wrong). I would expect that trees are naturally productive since fruiting is their means of reproduction. I want to know why this is the case (or even if it is the case at all, since up to this point I have not found any studies or convincing evidence of a measurable difference in yields or health of the tree). There are two good explanations I know of. First, pruning reduces the energy and nutrient requirements by reducing the amount of vegetation (much like removing suckers on, for example, a tomato plant) which promotes more vigorous growth in the remaining vegetation. Second, by opening up the tree more sunlight reaches each individual branch and this promotes more vigorous fruiting. Whether either or both of these explanations is true I do not know.

Additionally, I recently watched the DVD "The Permaculture Orchard : Beyond Organic" (which I thought was excellent by the way, I would recommend it if you have any interest in growing fruit trees even on a small home scale). In it they talk about training the branches downward to drastically reduce the amount of pruning needed. The explanation given was that when the branches grow upward the tree produces hormones that promote vegetative growth. When the branches bend downward the tree produces hormones that promote fruiting. While this may be less labor intensive than pruning, it still involves the orchardist doing quite a bit for the trees, so I still wonder why trees would be so bad at producing fruit on their own if that is how they propagate themselves (one possible answer may be that trees simply don't need very much fruit to propagate themselves, and having more vegetation and less fruit per year is somehow beneficial to that end).

Now for my very limited observations. The house I grew up in has two fruit trees in the back yard, one apple tree (I suppose to be standard size at around 30 ft (4.5m)) and one pear tree (I suppose to be a semi-dwarf at around 15 ft (2.25m)). I do not know the varieties, but they are both decent tasting. I suspect they were both grafted because of the good fruit, but I did not see the typical mark around the base of the tree tell-tale of grafting (but given their age that very well may not be visible, especially to my untrained eye). To my knowledge they were never pruned up until last year when I decided to do so (though now I wish I would have left them alone for more careful observation). At the very least, they were not pruned for the 20 or so years my family lived in the house (they were planted before we had the house though so they may have been pruned when younger by previous owners). Every year they fruit quite well (though I don't have anything unpruned to compare them to, but I always thought they produced a lot of fruit for something we never pruned, sprayed, fertilized, or otherwise did anything to really). They have had no disease problems that I know of.

After watching the permaculture orchard DVD I started thinking about the form of the trees on the property. I realized that most of the branches on both trees were bent downward even though no one had trained them for at least 20 years. This downward bend was especially pronounced on the larger apple tree. Also, older/larger branches seem to bend down much more than younger/newer growth.

So here is my theory based on all of this: perhaps fruit trees have a strategy by which they first send all of their energy into vegetative growth, primarily upwards at various angles. This establishes the tree so that it is more resilient (e.g. wind storms, snow, etc.) and shades out weedy undergrowth by producing a dense canopy (as opposed to the very open canopies of pruned fruit trees. After sufficient establishment, the branches naturally bend downward due to their weight (since they are getting larger and further away from the trunk). When they bend downward this signals the tree to produce the fruiting hormones as opposed to the growth hormones (I know nothing about these hormones, so that is taken entirely from the DVD). As the tree gets older and more and more branches begin to bend downward, fruit production continually increases.

This theory might also explain why pruning is so prominent. Even though (if this theory is right) fruit trees are very productive when left to their own devices, they take a long time to get to that point. When you prune it is much more work but there are more immediate results. If it takes 5-10 years to get full production with pruning, and 20-30 years without, almost any typical commercial orchard is going to be willing to invest the work to get fast results (of course these time frames are very uneducated estimates, so the discrepancy could be much greater or much less).

The implication I am most intrigued by is that if this theory holds true, then you could have a very productive orchard with virtually no maintenance, but it would take a little longer to establish.

Considering these are very limited observations and my very limited knowledge, I am eager to hear about others thoughts and observations. Do you have any observations you could provide which would support or deny this theory? Or perhaps a relevant study or book on the subject?

Thanks in advance!

Hi Emmett.  Welcome.  Thanks for starting such an excellent topic.

A couple of thoughts come to mind regarding they "why" of pruning.

First, it seems somewhat counter-intuitive, but when you are growing trees for fruit, less blossoms and less pollination is often better than more.  If you are feeding your soil regularly (mulching, top dressing with compost, etc.), and you have adequate moisture and sunlight, your trees will grow aggressively.  They will also bloom aggressively and will attract a lot of bees.  Suddenly, you are faced with the problem of having way more pollinated blossoms than your tree can reasonably support, so you have to get out there and thin the fruit.  There is an optimum amount of fruit set that you want.  An un-pruned tree will usually over-fruit set, leaving you a lot of extra work to thin it.

Second, related to the first point, it's hard to reach up into the branches to thin and pick when the tree scaffolding is so thick that you can't get your body into the inner structure of the tree.  The old saw is that you want to prune heavy enough so that a bird can easily fly through, but not so much that you could throw a cat through it.  (I love that visually imagery --- a cat flying through the air).  For my mature trees, I like to be able to walk right into the heart of the tree and be able to reach all the fruit growing within the heart of the branch scaffolding.  So for both thinning and picking, I like the structure of the tree to be open enough so that I can easily reach all the fruit.

Third, and perhaps this is obvious: I want large fruit.  Quality is more important than quantity.  It's hard to do much with a small apple, once you've pealed it and cored it.  So one large apple is better than 3 smallish ones.  Having twice as many branches producing twice as many apples doesn't make sense.  In a permaculture garden, production usually outpaces your capacity of use all your produce, so I'd rather have big healthy fruits and veggies as opposed to buckets and buckets of small fruit.  With the exception of citrus, cherries, apricots and avocados, I thin all my fruit trees to get nice large fruit.  I've got about 20 different pom fruits and stone fruits --- all of them are thinned ruthlessly.  40 good-sized peaches is preferable to 100 little dinky fruits.  Thus, you prune away a lot of the extraneous branches so that the tree's energy is focused on much less fruit.

Fourth, the goal of pruning is to allow sunlight to penetrate into the tree and feed the lower limbs without wasting a single photon onto the ground.  That's a tricky balance.  In my case, I've got a lot of good stuff growing beneath my fruit trees—ginger, herbs, comfrey . . . so I don't mind a bit more sunlight shining all the way through.  At the end of your pruning, you want every branch to be equally productive: both those at the very top as well as those on the lowest levels.

Fifth, heavy, drooping, leggy branches are an invitation to snap-off.  There is an art to finding that balance between letting the tree express its tree-ness, and doing what is best for it in the long-run.  It's a bit like parenting children, finding the balance in giving structure for healthy maturation without over-parenting.  A mature forest imposes a structure upon the trees growing within it.  In a mature old-growth forest, only one baby tree ultimately grows to replace the 1000 year-old beech or redwood that parented it, despite the millions and millions of seeds that are produced.  But in a garden, we have to impose that structure upon the trees therein.  Gently shaping the tree over time, taking your time and being prudent in your selection of what to trim and what to leave . . . be an attentive parent, but not controlling.  Over the years, you'll get to know your individual trees and have a sense for how they do best.  

Finally, related to the idea of allowing sunlight to filter through and equally hit all the branches of the tree, top and bottom, inner and outer, you also want airflow to move through your trees equally.  Fungal diseases more readily spread in densely bunched branches where the air can't circulate and keep things dry.  I'd rather have the sunlight and the breeze take care of those fungal spores rather than have to spray to control them.  So you don't want just the tops and outsides of your tree to get airflow, but also the inside.  Rubbing branches are an invitation for a sore to develop along a branch, making an opening for a pathogen to enter.  

Those are just a few thoughts.

Here is the best video I've seen on the "how" question, although he does touch a bit on the "why" question.


Best of luck.

My philosophy is different to marcos for different reasons . I have lots of trees about a hundred . The time for pruning is also the busiest time for me in the veg patch plus work wise . So I concentrate on grafting and planting new trees , this work is at a slack time of year I recon to create about ten to twenty new trees every year in ten years time I will have over 300 trees whilst if I followed Marcos philosophy I would still gave about 60 which is what I started with.
I feel this is the most resilient option for me
David

Just about every fruit that man has domesticated, grows a much larger fruit now, than it did originally. Wild apples are about the size of the tip of your baby finger. Wild plums can be the size of a grape. The tree doesn't necessarily know this, and may put on so many blossoms, that the fruit reverts closer to the natural size. This greatly increases harvesting time.

Young trees can set enough fruit to cause them to split up the center, or break off at a graft line.

I believe some pruning is in order but I mostly deal with a) branches that cross b) stuff that might otherwise split c) can I get under it d) 'twigging' (removing stuff that has died). Twigging can be done any time you have a few moments, it is just cutting back stuff that died to the living growth. Crossing branches is my next big issue, getting them while small is best. Then is can I get under it, to maintain the ground under inside the dripline and remove windfalls (we have horrible hornet issues so I remove them) Stuff that might split is where I find a weak V that might split with load.

Or topping something that decides it's growing to heaven instead of branching out. I have a few trees that need reminding they need to grow sideways as well. On all, if I have viable living wood I will take the cuttings and try to propagate them. Sometimes it's successful, sometimes not.

Another reason for removing windfalls, um, volunteers growing where you don't want. I will dig out and remove those, but still.

Thanks for the responses! It sounds like there are a variety of reasons one might prune, but I am going to be stubborn. Are my trees simply crazy anomalies? I will readily admit 2 examples is far from a sufficient sample size to draw serious conclusions.

Let me just address a couple of the reasons for pruning and say why I am not convinced.
1. To increase fruit set: it seems to me that this is purely for the sake of enlarging the remaining fruit. That is all well and good if that is what you want. Certainly this works very well (just look at the apples in the grocery store that are twice the size of your fist to see the results of good pruning!). But I question that the fruit would be so small as to be burdensome or useless. Again I only have my two trees as examples, but before pruning the fruit on those trees was perfectly sufficient for eating, or any other use one might use them for. For the average american consumer who likes massive flawless apples they might not fly, but as far as I could see (and to be hoenst I did not examine them closely) they were very suitable for my uses and likely many other peoples as well. Is the fruit typically that much smaller?
2. To decrease disease and breakage: again this seems so odd to me. Unless these are a sort of "natural" pruning and don't really harm the tree (which from the sounds of it is not the case) then it baffles me how something in nature could so consistently harm itself. It seems that these things are typically anomalies in nature, and for the most part the way a plant grows/behaves is quite beneficial to it's health. No one is walking around in the woods pruning trees, they grow on their own and seem to do a fine job at it. Granted, when human breeding affects a species it might bring a long with it a few unintended consequences (I am by no means anti-breeding though), but it seems to me that fruit trees are so similar to wild trees in structure that it would seem very odd that they would face great odds of harm when left to their own devices. It seems likely that pruning helps prevent these things (I am not under any delusion that no disease or harm exists in nature), but if left unpruned are the trees really facing that bad of odds? It seems to me it may be only a marginal difference.

So I suppose what I am saying it, I see that pruning has some benefits, but what I wonder is how big are those benefits? How necessary is pruning?

Are there any studys that compare yields or fruit sizes? Has anyone personally observed a tree that was never pruned from the beginning develop in to a small fruiting, disease riden, or otherwise useless tree?

I know you all have so much more knowledge than me, but my two trees have really made me question everything I read about these things. I hear what other people say, and it simply doesn't correspond to what I see! I know my two trees are not representative of the whole of all trees, but I would like to hear of others direct experience with these things.

I hope this post does not come off as condescending, as if I think I know better. I certainly don't know better! But that is exactly why I ask these questions, which to the more experienced and knowledgeable probably seem so silly!

I can certainly compare pruned to unpruned trees, as I've had years where I wasn't able to get to all the trees in my orchard.  Yes, the quality of the fruit on the unpruned trees suffers.  Is it drastic?  No, not terribly drastic, but there is a clear difference between those trees that have been pruned.

For me, a larger issue is thinned or unthinned.  Particularly on apples, peaches, nectarines and pomegranates.  If I don't thin 80 to 90% of my pomegranates, the fruit I end up with is hardly worth the time to try to eat.  But pomegranate trees are poky with little thorns on the ends of the branches . . . so, you've got to prune the branches in order to get up into the tree and thin the fruit.  Plus, I've found that when I aggressively prune, there is less damage from the ants -- can't explain why, other than ants like it when two pomegranate fruits are touching --- it seems to give them an avenue to get into the fruit somehow.  So if you want big beautiful softball sized pomegranates, you've got to prune and thin.  Additionally, that's what sells.  Customers know that there is going to be much more eatable fruit per pound on a large pomegranate than a small one, as the pom to peel ratio goes up with larger fruit.

Apples are hard to work with when they are small, because once you peel them, there isn't anything left.  We like to dry about half our crop --- peel them, core them, slice them into rings, toss them in a little lemon juice, and then sun dry them.  That's next to impossible to do with small fruit.  Yes, I can feed the scrawny little fruit to the chickens, but if you want to peel the apples and make pies, sauce or dried rings, you need something decent sized.  

I suppose that to each his (or her) own.  If you don't mind smaller fruit, more power to you.  The wisdom of pruning trees is pretty well established, going all the way back to Biblical references and even before.  But experiment and see what works best for you.  Best of luck.