The potato plant (Solanum tuberosum) is a staple crop worldwide, but it holds a critical secret: only the underground tuber is safe to eat. All other green parts of the plant—including the leaves, stems, sprouts, flowers, and any green-tinged skin on the tuber itself—contain a toxic compound called solanine. Solanine is a glycoalkaloid, a naturally occurring defense mechanism the plant produces to protect itself from pests and diseases.
The Dangers of Solanine
Solanine acts as a neurotoxin and can cause a range of serious health problems in humans and animals. The level of toxicity depends on the amount ingested and the individual's body weight. Symptoms typically appear 8 to 12 hours after consumption but can occur much faster, within minutes, with a high enough dose. Cooking does not effectively eliminate solanine, as the compound is heat-stable and only degrades at very high temperatures.
Why Green Means Danger
When a potato is exposed to sunlight during growth or storage, it starts producing chlorophyll, which turns the skin green. While chlorophyll itself is harmless, its presence is a clear indicator that the plant is also ramping up its production of toxic solanine. This is a natural defense response to perceived threats. Therefore, greening is a visual cue for high solanine levels, making the potato bitter-tasting and potentially hazardous. Any green spots on an edible tuber should be completely cut away before cooking.
Sweet Potato vs. White Potato: A Key Distinction
It is crucial to differentiate between the true potato (Solanum tuberosum) and the sweet potato (Ipomoea batatas). Despite the name, sweet potatoes are not in the nightshade family and belong to the morning glory family. The leaves of sweet potatoes are, in fact, edible and highly nutritious, often consumed as a leafy green vegetable in many parts of the world. This critical difference is a source of common confusion for gardeners and cooks.
Edible vs. Toxic Plant Parts: A Comparison
| Characteristic | Potato (Solanum tuberosum) | Sweet Potato (Ipomoea batatas) |
|---|---|---|
| Family | Nightshade (Solanaceae) | Morning Glory (Convolvulaceae) |
| Edible Parts | Underground tuber | Tuberous root and leaves |
| Toxic Parts | All green parts: leaves, stems, sprouts, flowers, green skin | None |
| Key Toxin | Solanine | None in leaves/stems |
| Taste of Leaves | Bitter and inedible | Mild, spinach-like |
| Storage | Cool, dark place to prevent solanine build-up | Cool, dark place for roots |
Proper Handling and Storage
To minimize the risk of solanine poisoning, always handle potatoes properly. Store potatoes in a cool, dark, and dry place, as exposure to light encourages solanine production. Avoid storing them in the refrigerator, which is too cold and can alter their flavor and increase solanine levels. If you notice a potato with a green hue or sprouts (eyes), you should cut away all affected areas. For very green potatoes or those with a bitter taste, it is safest to discard them entirely.
Composting and Disposal
For home gardeners, knowing how to safely dispose of potato leaves and stems is important. The best method is composting. Plowing them under the soil after harvest is a common practice among farmers to enrich the soil. While the composted material is safe, it is essential not to use un-composted leaves or stems as mulch or a top dressing in areas accessible to pets or children, who might be tempted to chew on them.
Recognizing Solanine Poisoning
If someone accidentally ingests toxic potato parts, they may experience symptoms that range from mild to severe, depending on the dose.
- Gastrointestinal Distress: The most common effects are nausea, vomiting, abdominal pain, and diarrhea.
- Neurological Symptoms: In more severe cases, neurological signs can include headache, dizziness, hallucinations, and confusion.
- Other Severe Effects: Serious poisonings can lead to paralysis, fever, dilated pupils, and in very rare, extreme instances, death from respiratory failure.
If you suspect solanine poisoning, seek immediate medical attention. Contact a poison control center or emergency services for guidance. The prognosis for full recovery is generally good with prompt treatment.
Conclusion
Ultimately, while the potato tuber is a safe and nutritious food, the rest of the plant is not. The leaves, stems, and sprouts of the potato plant are toxic due to the presence of solanine. Safe gardening practices, proper storage, and knowing the critical distinction between regular potatoes and sweet potatoes are the keys to avoiding accidental poisoning. By remaining vigilant and respecting the potato plant's dangerous parts, you can safely enjoy this popular crop for years to come.
Visit Poison Control for more information on solanine toxicity
