Loosen soil between the rows using a garden fork. Use a rake or spade to draw the soil into a ridge along the length of the row around the emerging stems of the potatoes. Leave a shallow trough along the row at the top of the ridge to channel any water down to the developing tubers.
When growing potatoes in large pots or sacks, the tubers will have been planted into 10cm of compost at the base of the container. As the shoots emerge, add more compost at regular intervals, 5cm at a time, until the container is almost full.