Volunteer potato

Potatoes are often seen growing as casuals on tips and waste ground but it is the volunteer potatoes found in arable fields that are the weed problem. These arise from seeds, tubers and tuber pieces that remain in the soil following an earlier potato crop. After potato harvest there may be as many tubers left in the soil as were planted originally. Volunteers that grow from missed or ground-keeper tubers develop vigorously and are difficult to eliminate in poorly competitive crops like leeks and onions, particularly from within the crop row. 
Once shed, potato seeds can remain viable in soil for 3-9 years. The seeds will also remain viable for long periods in dry-storage at low temperatures.