I never pull out old plants, just make new rows every three years. Use the new plants created by the runners. The crowns of old plants will be woody.
To clarify, after using new runners for new row, the old row is tilled under. We keep three rows going at a time, then each year one row gets tilled under (you would need space for four rows, three to use and one to till under.) i don't know if this makes sense to you or not.
