You collect them stirckly yourself? No carbon-consuming tech involved?
I do not want to descend into some kind of “but there is always some carbon” point, I just want to point out that a robot powered by, say, solar electricity can be more green than a human-powered broom, production costs included.
Neither of the two is perfectly green, but a solar-powered robot is more efficient in leveraging solar power than human growing and eating plants.