Translated from the Polish forum of Gamedesire:
Plants grow like real plants. So next to the tree there is a chance that there will be a small tree or grass, bush, mushroom, etc. Near the grass there is a chance that you will see grass or mushrooms and herbs. Next to other herbs there is better chance that there will be other herbs, etc. so mechanic is quite realistic. Suddenly there is no chance that something has grown in the middle of an empty board. In addition, the increase iterations are calculated from the period of inactivity in the game. You have to be inactive 12h. For your eyes nothing will grow 🙂
Source: link (Polish).