Green in the garden is a good sign of healthy, happy plants, unless you are a potato. Potatoes that are exposed to the sun will start to produce the green pigment, chlorophyll, at the surface of the potato. This process is called “greening”. The problem is not the chlorophyll but the other compound that is produced along with chlorophyll, solanine.
Solanine is good for the potato
Solanine is produced in the skin and not much deeper than about an 1/8”. It gives a bitter taste to the potato and is thought to cause avoidance by insects and animals. So producing this compound is great if you are a potato, but not good to eat. If eaten it can cause gastrointestinal irritation and if enough is consumed, vomiting and diarrhea.
What to do with a green potato
The good news is that most of the solanine can be removed by simply peeling away the green skin. If there is a lot of green under the skin, the potato should be tossed into the compost pile.
Preventing “Greening” during storage
Potatoes can develop the solanine when growing in the garden and also during storage. Store in a cool dark place like a cellar or basement. Other stresses can cause solanine production like cold, heat or injury, so handle and store your potatoes away safely.
Preventing “Greening” during growth
Greening can be prevented if the potatoes are covered with soil or something like straw to prevent sunlight from reaching the precious tubers. Continue to hill the potatoes as they grow and additional mulching with straw will not only help conserve water but help keep the light out from the potatoes that grow close to the surface.