How many adjacent squares of forest do I have to plant before they will begin to expand?

And is there a formula, such that the more adjacent forest squares, the greater chance of auto expansion?

1 Answer 1


I don't have an authoritative answer, but I believe that each turn, each forest square has a very small chance of expanding to a random adjacent square. So the more forest squares already on the map, the more random forest square expansions will occur per turn. I believe this expansion mechanic also applies to fungus, but is less noticeable to the player since the game doesn't notify you of fungus expansions like it does for forest expansions.

  • 1
    Note that this means that for the best effect, you should plant in a checkerboard pattern so that every tile of forest has the maximum possible free adjacent squares to expand into. Jun 12, 2019 at 11:43
  • Great suggestion, thanks! I have been planting in contiguous blocks.
    – Mawg
    Jul 6, 2021 at 6:08
  • @Mark "the game doesn't notify you of fungus expansions" - I have seen it do so
    – Mawg
    Jul 6, 2021 at 6:08

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