The staple crop of the highlands was the potato, which unlike maize regularly grows at altitudes of 14,000 feet; the tubers, cultivated in hundreds of varieties, can be left in the ground for as long as a year (as long as the soil stays above 27degF), to be dug up and cooked when needed. Even frozen potatoes could be used. After letting freezing night temperatures break down the tubers' cell walls, Andean farmers stomped out the water content to make dried chuno, a nigh-indestructible foodstuff that could be stored for years.