Last year I took my trusty pruning saw and cut down a couple small (2″—3 ½”) diameter trees growing where I didn’t want them to. I left quite a bit of the stumps remaining. Wanting to ease the job of killing the stumps I poured ordinary table salt in holes or defects in the stumps. Given time, the table salt will eat away at the stumps and they will rot away.
Although this method is slow it is effective for places where time is not a major issue. There are no toxic chemicals involved, and the cost is very low.