I worry more about growing strong root systems than I worry about top growth. One thing I keep wondering is about the modern custom of smaller trees that are planted closer and closer together, when you pair that with water shortages.
An apple tree planted in half decent soil without competition will send roots 8’ out, 8’ deep by the end of the second year. Grow anything near, and the roots stop spreading. Even sod on top will dwarf root development both sideways and down. A tree with a wide (and deep) root area becomes a whole lot more drought tolerant; it simply has a lot more real estate to try and find humidity.
I realize that a commercial or semi-commercial operation cannot afford anything other than high density and lots of irrigation, but for the rest of us if water is an issue then high density may also be an issue, it forces the orchard to need constant irrigation.
I don’t think the problem is the small tree but how they get deployed. If you allow the roots to roam they could be every bit as hardy but then again, that’s not how they are usually planted.
Another interesting bit is that you can indeed make a tree hole larger after the fact.
I have one of the most horrid 50/50 gravel/rocks soil. Heck in a sense I mine my soil; I have various screens so digging up a hole for a tree gives me sand, gravel for the winter, larger gravel for concrete, and larger round river rocks for landscaping. It is interesting to see how in a summer day on a fresh hole the ground is downright hot a foot down, them rocks and sand transfer and retain heat pretty good. Under the mulched trees the earth is cool right under the surface.
Anyways… The roots can’t really penetrate the sand/gravel, so next year I’ll continue to dig around the tree another foot beyond the original hole to extend the much and overall tree soil area. The roots greedily take over the newly available good soil. My trees are about 14 feet apart. Ideally I would continue this until the areas touch each other. I wasn’t about to dig a 14’ hole per tree from the get go but given enough time I may get there one foot at a time.
On a side note I don’t worry about my romance cherries as much. They roots go all over the place regardless of what may be planted around them. They are particularly good at straddling the line between top soil and gravel underneath just bellow the grass root area.
We have an overabundance of water here. I wouldn’t plan a high density orchard because I find them unsightly and they are probably too much work for me. I’m lazy