The Forest is created by putting Rosemary on Barren Land. Some Plants that spread on the Forest Biome include Sage, Heather, Tall Tree, Juniper Tree, Fern, Cedar Tree, Potato Plant and Acer Tree. Rosemary is the cheapest and easiest to spread and start off the Forest Biome with. An area that contains 5 out of the 8 plants that spread should give you 100% Forest. To get 100% there needs to be no plants that spread other biomes within it e.g. Grass Tuft, Daisy etc.