As many know already, I'm not a big fan of what I call dummy rules. The dummy rule phenomenon as roughly defined by me, is a broad rule statement with either minimal context, or lack of context, stated dogmatically without qualification as a should and/or shouldn't proposition. As a social phenomenon, the less experienced will often take these absolute statements as absolute, which shouldn't be surprising, and use them as both weapon and battlecry in their petty wars on "misinformation" against people like me with enough experience to understand that there are such things as nuance and context. Lol, good luck with that.
Rules of thumb are a different matter. Many dummy rules probably start as rules of thumb, or contextual statements and are mutated into nonsensical dogmas that retain just an "element of truth". If I were a different kind of person this article and video could be more along the lines of... "Today I'm going to show you how to "properly" thin apples. Thin the apples when they are such and such size to such and such distance apart." But alas, life is more complicated than that, as we all find out when we start doing things and not just reading about them. I think I remember reading in Michael Phillips book on apple growing (but am too lazy to look it up) that there was a study showing a diminishing finished apple size if you thinned the trees after applets reached the size of a nickle. In other words, if you wait too long to thin, the remaining fruit may not grow as large as it would if you thin early. Let's assume I remember correctly for argument's sake. It would be easy enough to take that and create a dogma.. "always thin you apples by the time they reach the size of a nickle!". Not to say Michael said that, which I doubt, but this information can easily lead to that kind of thinking.
Context, however, may dictate other approaches. First off, all apples do not set at the same time on a tree, so there are can be a large variation in size. Should I thin everything for sure as soon as the first apples reach the size of a nickle? Maybe I average that out and and let some get to the size of a quarter and thin when most of the apples are around nickle sized. Maybe I thin early, because I have time and may not have time later. Another thing experience teaches is that I may want to give diseases, pests, weather phenomenon or other environmental factors a little extra time to beat up on my fruitlets, so I can thin the resulting damaged ones, and leave the ones that have remained unscathed in early summer. Now we are in the realm of real life, life as art and as adaptation and cumulative knowledge... the realm of context.
I use the handspan rule-of-thumb quite a bit when thinning apples. That is to say that a good distance for apples along a limb is about a span of thumb to forefinger extended, like the Shaka/Hang Loose hand gesture of Hawaiians and surfers, about 7 or 8 inches. But, that is a contextual guideline, not a dogma. So many different things can affect the decision of spacing, and the decision to leave or not leave pairs or even three or four apples in a cluster. If I say simply a handspan apart, but there are only 20 apples on the tree and thinning to singles at hand spans would leave 5, that would just be dumb. Also, how large is the fruit of said apple variety? I'm not going to use the same spacing on a 1.5 inch apple variety as I would on 3 inch apple varieties.
Another thing to think about is how much you are likely to lose early in the season to burrowing insects, birds and other diseases, pests and phenomena. Maybe I'll leave a few extra for now and thin more off later. Finally, where are the apples located on the branch? If they are gregariously clustered into denser groups, then I might space actual apples closer and be looking to leave an amount that would be similar to what would be left with an apple every 7 inches along the branch if they were spaced perfectly all over the tree. The handspan is a very useful guideline, but it is just a point of reference that not only doesn't always just play out like clockwork in real life, but probably rarely does so. So, it is not the spacing itself that matters, but total fruit load, placement, environment, goals, style, timing and so on.
Lets back up a bit here, thinning can be done for the following reasons.
To get rid of diseased, oddly shaped, damaged and poorly pollinated apples. Worthwhile even if the tree is not crowded.
To avoid fruit touching one another on the tree. Touching fruit is a common site for insect infestation.
To avoid broken branches. Overbearing is probably the most common cause of broken branches.
To increase the average fruit size. Very important in commercial production, though few home producers are much concerned.
To spare the resources of the tree, which can encourage yearly cropping instead every-other-year cropping. Most trees left to their own natural tendencies will fall into biennial cropping.
When I approach a tree for thinning, I look at several things right away.
How big are the applets? It is tempting to thin early, but I like to wait a bit so that scab can take hold and become obviously visible, bugs can do a little damage, unpollinated or poorly pollinated applets can be rejected and our hail season is more likely to be past us. That way I can take out all those newly damaged apples, leaving a sizeable crop of good ones. The information about thinning by the time apples reach nickle size is only one piece of information in these decisions, assuming it's true that is. The rest has to be intuition, experience and as much as anything guesswork. Personally, I hardly blink about fruitlet size until quite a few start to hit quarter size or start going over.
How many fruits are on the tree? A lot of fruits on the tree means larger overall spacings between apples, relative to the normal fruit size of that variety of course. If there are very few, I will leave them close together and even in clusters. It is better not to leave doubles and clusters, because it's a favorite place for insects to lay eggs or set up camp, but again with the context.
How large is the branch? How much weight will it support?
Am I greedy this year, or striving to maintain annual bearing? Or maybe I just DGAF. Most trees will fall into biennial bearing easily, meaning that they will produce a lot one year and little to no fruit the next. The tools you can use to try to prevent that scenario are adequate thinning and good cultural care. Unless I make a real effort, most of my trees are going to be pretty biennial, because my cultural conditions are not great. I can live with having king david apples only once every other year. I've got bigger problems to tackle. In a more ideal world, I'd try to get crops more consistently.
Thinning apples, just like training and pruning trees is more art than science for a small holder like me. It is different in the context of monocropping, where there is more repeatability and predictability. For the average backyard and home orchardist, thinning in a couple of phases works pretty good. In fact, after editing through my video and writing this, I think that is a great approach to recommend and ultimately something like what I practice. Thinning in two stages takes off a lot of pressure for those just learning about this task, who will always want to leave too much fruit anyway. It also encourages observation which can help inform future work. Go through quickly once when the apples are under quarter size for the most part and take out the great majority of what you will take out in the long run. Leave the best looking undamaged fruits and some extra. Come back in two or three weeks and you'll start to see that there is more fruit there than you thought you left. Take out a little more and some that have taken damage or where flaws have become more apparent. A stroll through your trees every few weeks will allow you to see the results of your practice and give a chance to keep removing damaged fruits. I pick off wormy and bird pecked fruit through the growing season. Everyone has those right? If not, where do you live?, I'm moving there buddy! Your context is your own. Don't over-think it, obsess, or spend too much time deciding what fruitlets to leave or how many, but don't under-think it either, because it does require forethought and knowledge. As small scale growers we may often be able to afford the luxury of these pleasant strolls to micromanage the fruit over a period of time and observe the effects of our activity. I love thinning my apples and checking on their progress.
I'd be interested to hear from others of you that have thinned apples for a while and what kind of rules of thumb you use or how your context and life affect your approach to thinning fruit. Happy growing and best wishes for a good fruit season. <3