Article and Photo by Gary Predoehl, UC Master Gardener of Placer County
“He who plants gardens plants happiness.” – Chinese Proverb
“Gardening is cheaper than therapy – and you get tomatoes!” – Unknown
Raw vegetables are an important part of a healthy diet. But many common garden vegetables contain natural toxins that gardeners should know about. In some cases, these compounds can cause skin rashes, nausea, digestive problems, fever, or weakness. Serious illness is rare, but a little knowledge can help keep your harvest safe and enjoyable.
One of the most common groups of garden vegetables is the nightshade family. This group includes tomatoes, potatoes, eggplants, bell peppers, and chili peppers. For centuries, some Europeans believed tomatoes were poisonous and grew them only as ornamental plants.
Today we know that the fruits of tomatoes, peppers, and eggplants are safe to eat. However, the green leaves and stems contain a natural toxin called solanine. Plants produce this compound to protect themselves from insects and other pests. (California Master Gardener Handbook, Second Edition, Dennis R. Pittenger, Editor, UCANR Pub. 3382, 2015, pp. 674-675)
Potatoes deserve special attention. If a potato has green skin, green spots, or has started sprouting, solanine may be present in the tuber itself. Cooking does not remove this toxin. Discard green or heavily sprouted potatoes. Otherwise, potatoes remain a nutritious food enjoyed around the world. (California Master Gardener Handbook, Second Edition, Dennis R. Pittenger, Editor, UCANR Pub. 3382, 2015, pp. 674-675)
Another important group of vegetables is legumes, or beans. Beans are nutritious, versatile, and widely eaten. However, some raw or undercooked beans contain a natural toxin called phytohaemagglutinin (PHA). Red kidney beans contain the highest levels. Eating only a few raw or improperly cooked beans can cause severe digestive distress. https://nutritionsource.hsph.harvard.edu/anti-nutrients/lectins/ A Publication of Harvard University School of Public Health
Fortunately, proper preparation makes beans safe to eat. Depending on the type of bean, this may include soaking, boiling, or both. Follow cooking instructions from reputable sources, and never eat raw beans. Also, avoid preparing dried beans in a slow cooker alone, since it may not reach temperatures high enough to destroy the toxin.
Finally, there is the cucurbit family. This group includes zucchini, summer squash, winter squash, pumpkins, cucumbers, melons, and gourds. These vegetables are generally very safe. However, under stressful growing conditions such as extreme heat, drought, poor soil, or inadequate nutrition, some plants can produce unusually high levels of a bitter compound called cucurbitacin. https://pnwhandbooks.org/plantdisease/host-disease/squash-cucurbita-spp-toxic-squash-toxic-zucchini A Publication of Oregon State University Extension Program
Plant breeders have largely reduced this compound in modern varieties, so problems are uncommon. Still, excessive levels can occasionally occur, especially in zucchini and other squash.
The warning sign is easy to recognize: an extremely bitter taste. If a zucchini or squash tastes unusually bitter, do not eat it. Throw it away. Cucurbitacin can cause serious illness, and cooking will not remove it.
The purpose of this article is to educate, not alarm. The vast majority of vegetables grown in home gardens are safe, nutritious, and delicious. By understanding a few basic precautions, you can confidently enjoy the bounty of your summer vegetable garden.