Weeds. I understand that weeds mostly invade soils that need them (!). They provide biomass (humus when dead), their roots bring up moisture, they break up the hard pan, and convert rock to minerals that plants can use. So in theory once they have done their job, they would move on and the soil where they were will be more amenable to raising something else in the soil that they have improved.
Hmmm. So how do you get them to move on instead of taking over your place?
