Bava Batra 26 - Tree Roots in the Neighbor's Field
The previous ruling dealt with planting a tree in a location where its roots might damage a neighbor's pit. This one discusses a field with plants but without a pit.
One must not plant a tree near his neighbor's field unless he distances the tree four amot (6 feet) from his neighbor's boundary. This distance is needed to provide sufficient space for the cultivation of his planting without encroachment on his neighbor's property. If there is a fence, no distance is required.
If the roots of the tree extended into the neighbor's property, the neighbor may excavate three hand-breadths deep and remove the roots, to facilitate his plowing. If the neighbor was digging a pit and came upon roots, he may cut downwards to whatever depth he finds necessary.