You need to cut away all green potatoes after harvest before you cook or eat them. The green color warns you that toxic compounds have formed in that part of the tuber. A generous trim with a sharp knife removes the risk. You can still eat the white parts that remain.
I found a whole bin of green-tinged potatoes last winter in my storage room. The problem was a small window that let light reach one corner of the shelf. The tubers closest to that window had turned bright green on one side. I thought the whole batch was ruined until my neighbor showed me how to salvage them. I just cut away the green layer plus about half an inch of flesh below it. The rest of each potato was fine.
Potato greening happens when tubers get exposed to light. Any light will trigger the process. Sunlight does it fastest. But even dim indoor light or fluorescent bulbs can turn potatoes green over time. The tubers sense the light and start making chlorophyll. That's the green color you see on the skin and flesh.
The real problem isn't the chlorophyll itself. The danger comes from solanine in potatoes and other compounds that form at the same time. These glycoalkaloids are the potato plant's natural defense against pests. They taste bitter and can make you sick if you eat too much. Michigan State University says to remove green areas before you cook. The toxins build up right where you see that green color.
Symptoms from eating too much solanine include nausea, stomach cramps, and headaches. Serious cases are rare because you would need to eat a lot of green potato flesh. But why risk it when trimming solves the problem? The bitter taste usually stops people from eating too much anyway.
Here's how I handle green spots now. I peel the potato first to see how deep the green goes. If just the skin is green, I peel it off with a bit of extra flesh. If the green goes deeper, I cut away that whole section until I see only white or yellow flesh. I always err on the side of cutting more rather than less.
Some potatoes get too green to save. My rule is to toss any potato where more than one-third of the flesh shows green color. At that point, you would be cutting away most of the tuber anyway. It's not worth the effort or the risk when that much solanine in potatoes has formed.
Preventing potato greening is easier than dealing with it after the fact. Store your harvested potatoes in complete darkness. Use bins with solid sides, cover crates with dark cloth, or keep them in a closed cabinet. Check your storage area for any light leaks. Even the glow from a pilot light or a crack under a door can cause problems over weeks of storage.
My current setup uses wooden crates lined with newspaper and topped with old towels. The potatoes stay in total darkness and I pull out just what I need for cooking. I check the bin once a month and rotate the potatoes so none sit near the edges too long. Zero green potatoes since I started this method.
Your harvest day habits matter too. Don't leave dug potatoes sitting in the sun while you work. Put them in a bucket or basket right away and move them to shade. The greening process can start within a few hours of strong light exposure. Keep your tubers out of direct sun from the moment they leave the soil.
Read the full article: When to Harvest Potatoes: 6 Key Signs
