Potatoes grow from seed potatoes, which are small tubers with "eyes" or buds. When planted in the soil, the eyes sprout stems that grow upwards above ground to form leaves and stems, while underground stems (called stolons) grow horizontally. Tubers (the potatoes) develop at the ends of these underground stolons. The growing plant produces starch that accumulates in these tubers, which thicken and mature near the soil surface. As the plant matures, the leaves and stems die back, and the mature tubers detach from the stolons, ready for harvest. Farmers and gardeners typically plant seed potatoes in trenches or containers, covering them with soil. As the plants grow, they "hill" or mound soil around the stems to keep developing tubers covered and out of sunlight because exposure to light turns potatoes green and toxic. The tubers store energy and can produce new plants from their buds in the next season.