A potato plant is an herbaceous annual from the nightshade family that produces starchy, underground tubers (the potatoes we eat) at the ends of its stems. The plant grows leafy green shoots above ground, and as it matures, it forms tubers that are protected from sunlight by "hilling" – mounding soil or mulch around the stems to prevent them from turning green and toxic. The plant is ready to harvest when the green foliage starts to die back and turn brown.