"Earthing up
Potatoes can be 'earthed up' as they grow, bringing soil up around the shoots. This helps control weeds, prevents the tubers turning green and gives some protection against tuber blight. Do it first when plants are around 15cm (6in) tall, leaving a couple of inches of foliage showing. Earth up again just before the foliage meets across the rows. On a closer spacing, earthing up will not be possible, but the plants will shade themselves anyway.
Alternatively, the plants can be mulched with a thick layer of hay, straw, leaf-mould or grass mowings. This will have the added benefit of conserving moisture."
