How to Keep Potatoes from Turning Green | Light Is the Enemy

To prevent potatoes from turning green, store them in a cool, dark place away from any light source, including fluorescent lighting.

You reach into the pantry and pull out a paper bag of potatoes you bought ten days ago. Under the kitchen light you notice green patches near the eyes and along the skin. The color looks unappetizing, and you wonder if the whole batch is ruined.

Those green patches aren’t just a cosmetic issue — they signal that the potato has started producing solanine, a natural defense compound that can cause digestive upset at higher levels. The good news is that with a few simple storage habits you can stop the greening before it starts, keeping your potatoes fresh and safe.

Why Do Potatoes Turn Green

Potato tubers turn green when exposed to light during growth or storage. The green color comes from chlorophyll, a harmless plant pigment. But chlorophyll appears alongside solanine, a toxic glycoalkaloid the potato produces as a chemical defense.

Research shows that as potatoes turn green under light, both chlorophyll and solanine increase sharply due to the upregulation of specific genes. This means the green color is an effective visual warning — where you see green, solanine is likely present.

Light exposure is the main trigger, but the process can happen even under low-light conditions. Fluorescent lights in a grocery or kitchen are enough to start greening within a few days. The speed depends on light intensity and duration.

The Real Worry Isn’t the Color — It’s the Solanine

Many people assume green potatoes are simply unripe or sunburned. The real concern is the chemical that comes along for the ride. Understanding what solanine does explains why proper storage matters.

• Chlorophyll is harmless: The green pigment itself has no taste or health risk. It’s just a marker that the potato has been exposed to light.
• Solanine is the problem: This glycoalkaloid is a natural toxin concentrated in the skin and the green layers just beneath it. In sufficient quantities it can cause nausea, vomiting, diarrhea, and abdominal pain.
• Acute poisoning is rare but real: Medical literature notes that ingesting heavily green or sprouted potatoes can lead to gastrointestinal disturbances. Most cases are mild, but severe poisoning has been reported.
• Greening is a storage warning: If you see green, the potato has already started producing solanine. Adjusting storage conditions prevents further buildup in the rest of your batch.

So the green itself isn’t dangerous — but it’s a reliable sign that light has triggered the potato’s defense system. The solution is to keep that system from turning on in the first place.

How to Store Potatoes to Prevent Greening

Protecting potatoes from light is the single most effective step you can take. A dark pantry, a paper bag folded closed, or a cupboard away from the oven all work well. The ideal temperature range is around 45 to 50°F — cooler than room temperature but not as cold as a refrigerator.

University extension services stress that even fluorescent light can cause greening in a matter of days. The University of Alaska Fairbanks notes that greening occurs whenever tubers are exposed, whether during growth or in storage. Their to keep potatoes from guide recommends checking regularly and trimming any green patches before cooking.

Do not wash potatoes before storing them. The thin layer of dirt helps block light and keeps the skin dry, which discourages decay. Wash just before cooking instead.

Keep potatoes away from onions, which release ethylene gas that encourages sprouting. Sprouted potatoes also contain elevated solanine levels, so controlling sprouting helps control solanine risk.

Other Tips to Keep Potatoes Fresh and Safe

Darkness does most of the heavy lifting, but a few additional habits help extend your potato supply’s quality and safety.

1. Choose the right container: Use a paper bag or a perforated plastic bag to allow airflow. A sealed plastic bag traps moisture and promotes rot.
2. Store in a consistent cool spot: Avoid areas near the stove, radiator, or sunny window. Temperature swings can trigger sprouting and decay.
3. Inspect and rotate: Check your potatoes every week. Use the oldest ones first and remove any that show soft spots, heavy greening, or extensive sprouting.
4. Don’t store with apples or bananas: These fruits emit ethylene gas that accelerates ripening and sprouting in neighboring potatoes.

Following these steps reduces waste and ensures you’re eating potatoes at their best. The minimal effort of a proper storage setup pays off in longer shelf life and peace of mind.

What to Do If Potatoes Turn Green

If you find green patches on a potato, the first step is to assess how deep the color goes. Solanine is concentrated in the skin and the layer directly beneath it, so small, shallow green areas can be trimmed away safely.

The North Dakota State University Extension service advises peeling until no green remains and discarding any potato that tastes bitter. Their store potatoes in dark guide also recommends throwing out potatoes that are entirely green or have a strong bitter flavor, as these may contain unsafe solanine levels.

For heavily green or sprouted potatoes, the safest choice is to toss the whole tuber. The symptoms of solanine poisoning — nausea, vomiting, diarrhea — are unpleasant but usually resolve on their own. If symptoms are severe or persist, seek medical advice.

When in doubt, err on the side of caution. Solanine levels vary from potato to potato, and there is no home test to measure the exact amount. If a potato looks suspicious or tastes off, it’s better to replace it.

The Bottom Line

Keeping potatoes from turning green comes down to one simple rule: block the light. Store them in a cool, dark place, don’t wash them before storage, and check periodically for any greening. If you catch green patches early, trimming them away is generally safe. For heavily green or bitter potatoes, discard them.

If you’re ever uncertain about a specific batch, your county extension service or a food safety expert can offer guidance — the NDSU Extension’s online resources are a good place to start for practical, research-based advice.