Why are some of my potato tubers green?
Potato tubers are actually enlarged underground stems. When potato tubers are exposed to light (either in the garden or storage), their skin turns green due to the formation of chlorophyll. The chlorophyll itself is not a problem. However, higher levels of glycoalkaloids also develop in the green tissue. Green tubers have a bitter taste when eaten. They may also cause an upset stomach and more serious health problems.
Tubers with small green areas can be safely eaten if the green portions are cut off and discarded. It would be best to discard potatoes that are largely green.
When growing potatoes in the garden, hill soil around the base of the potato plants to prevent the tubers from being exposed to light. After harvesting, store potatoes in a dark location.