You say tomato, I say to-mah-to; you say potato, I say po-tah-to! The poisonous potato myth runs along the same lines as the poisonous tomato myth—somewhat true in the 1500s, but by the time the English were colonizing the North American coast, the fear had gone.
When the potato first came to Europe in 1562, it was variously thought to cause leprosy, to be associated with devil, to be an aphrodisiac, to protect against rheumatism, and to be poisonous. Quite a list of side effects, huh? (Propitious Esculent: The Potato in World History, John Reader, 2008, an excellent book, by the way.) How did this last myth get started? According to legend, Sir Walter Raleigh (or Sir Francis Drake, depending upon your legend) ate the poisonous potato berries, not realizing that the edible part is the part that grows underground, and got sick. He demanded the plant be destroyed. In burning the plant, the servant inadvertently cooked the underground potato, tasted it, and found it delicious. But the tale is impossible, since Raleigh never visited a potato-producing region in his life. Drake did, (western coast of South America in 1578) but he never mentioned eating or even seeing a potato in his journals.
One part of that myth rings true—the potato does contain a natural toxin called solanine that exists in the leaves, the stem, and green spots on the skin. It is certainly possible that someone, not Raleigh but some European, ate the wrong part and got sick. Others spurned it because it wasn’t mentioned in the Bible or because it resembled a leper’s deformed fingers and toes.
By the 1700s, potatoes had become part of the European diet for three main reasons. One, it is so nutritious that people can survive on nothing but potatoes (not happily, maybe, but it is supposed to be possible). Two, because potatoes grow underground, they can be left there until needed. That kept them safe from foraging armies in an era when Europe was engulfed in war. For peasants, potatoes acted as a food bank account, protecting them from starvation in times when other crops failed or were looted. And three, the plant grows well in the northern European climate.
By the 1560s, the potato was in Spain; by 1610 it had reached English Bermuda from England, and by 1620, it was in Virginia. By the middle 1600s, the potato was well established in northern Europe, Ireland, England, and Scotland.