Dead spots

[midnightpavo]

Across everyones' towns there are seemingly random spots that nothing will grow on. I have noticed that there are different types of "growing potentials" for each square. For example, a tree can grow on one spot, but a bush may or may not be able to grow on that same square.

What are everyone's thoughts on how things can grow in the tows? I would like to learn more on this aspect of landscaping that is rather annoying...