Where do you get weeds in the first place
In the old Autonauts (version 21.2) as shown below and similarly in the new Autonauts (version 125), the weeds appear naturally. In 21.2 they continue to grow again where they were dug from until you put fertilizer on the ground. In the new version, you must treat them as a crop because they are used in several foods such as Spiced Mushrooms.