In the picture below, I have separated my trees with 2 horizontal spaces and 1 vertical space from the next tree. They are all non-native trees and were planted on the same day. (The holes are for spatial reference and were not there while the trees were left for one night)
Why did the trees in the middle region not grow? The trees on the edges advanced to the next growth stage while those in the middle of the plantation pattern did not. Is there a probability where they fail to advance? Or is there a maximum number of plants that will advance to the next stage in a day? (Because I did plant a whole lot of trees and maybe I exceeded some maximum number?)
2 Answers
If there at 12 or more other trees (stunted, growing, or fully grown) in the 9x9 grid surrounding the tree, the tree will not grow.
For example the stunted tree near your head has 12 other trees trying to grow around it: 
To get your trees to grow properly you need to space them out more.
Alternately you can grow them elsewhere and then move them into this pattern. Trees won't grow this packed together, but if placed fully grown into this configuration they will still produce fruit, wood, and other tree resources.
3It's not just the spacing you have to worry about, the trees in the middle section aren't growing because of an issue where they're not getting enough sunlight. New Leaf also had this quirk. Move the trees to a different area and plant only one row at a time to avoid this.
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