Weeds

 are a food crop generated in a ring around other types of crops at the start of the game. They can be harvested with a spade to produce Weeds (Loose), but must be replanted in soil using after each harvest to continue producing more. They take 20 seconds to fully grow.

How to use
To avoid a situation where your farming bots run out of loose weeds to replant, they can be programmed to handle planting first and only store the remainder: