The overgrowth... it grows all on its own. (Inspired by @jonny0211 on the Factorio discord!)

The first tile of overgrowth is overwhelmingly expensive to create, but that one tile is all you need. Gleba's overgrowth will slowly spread and convert tiles of the matching terrain type to more overgrowth, impeded by native flora and pentapod nests. Walls can be used to stabilize the terrain around them and prevent overgrowth from spreading to places you don't want it to go. You can pick the new overgrowth up and relocate it elsewhere, but you can't recycle it back into its ingredients anymore.