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What does it look like our potato plants are growing… tomatoes?

Potatoes are now the most important vegetable in the world, and, not surprisingly, America’s favorite vegetable. We eat 147.8 pounds per person per year — as baked potatoes, fries, hash browns and more. There’s hardly a food service menu that doesn’t feature potatoes. Washington state grows more than 20 percent of all of the potatoes in the U.S, leads the nation in French fry production and has the highest per-acre yield in the world.

Although the majority of our commercial potato crop is grown in the Columbia River basin, the Skagit Valley is also recognized for its commercial production of red, white, yellow and blue potatoes. In fact, many Western Washington counties, including Thurston, Grays Harbor and Lewis at one time or another, were famous for their potato crops. Grays Harbor continues to be recognized for its production of the prized yellow Finns grown on the Lubbe farm, just east of Montesano.

Home gardeners have long recognized that our coastal climate and fertile soils are ideal for growing potatoes. Botanically, potatoes are tubers, the thickened underground stem of the potato plant, especially designed by nature for the storage of starch. Spud, a familiar term for the tuber, actually comes from the name of a turning fork used to harvest potatoes.

Most of our vegetable plants that flower eventually produce seed, and this includes potatoes. Gardeners are often surprised to see tomato-like fruit developing on their potato plants and often think their potatoes have somehow crossed with their tomatoes. These green “tomatoes” are actually the fruit (seeds) of the potato plant.

It’s not surprising that they look like tomatoes, since both plants are in the nightshade family. The potato seeds that form inside this fruit can be used to grow potato plants in next year’s garden as a novelty. But, in general, it is much easier to raise a crop from tubers than from true seed. Also, the resulting plants may not be as desirable as those grown from the tubers this year. Be prepared to start seeds indoors in winter, as plants are much slower to develop from seed than from tubers.

Do keep in mind that potato fruit are likely to be high in solanine, a substance that is toxic to humans, particularly children. Potato fruit should not be eaten, no matter how much they look like tomatoes!

Having trouble with potato tubers turning green?

Green potato tubers are caused by exposure to light, either while growing in the garden or in storage. This green coloration, which is also called sunburning, can be as much as a half inch deep in severe cases.

The greening is a sign that there may be an increase in the presence of glycoalkaloids, especially the substance solanine. When the potato greens, solanine increases to potentially high levels. Increased solanine levels are responsible for the bitter taste after being cooked. Because glycoalkaloids are slightly toxic, you can become ill if you eat too much of a green potato. Since most of the solanine is in or under the skin, simply peeling the potato will remove most of it.

One of the easiest ways to prevent the greening of potato tubers is by simply hilling plants. Pulling loose soil up around the plants prevents tubers from emerging through the soil and becoming green from the sun. Hilling also buries and kills weeds around the plants before they become a serious and time-consuming problem.

Donald D. Tapio is a regional gardening and farming specialist for Southwest Washington, having retired from Washington State University’s Extension Office. This column expresses his personal opinions and tips after decades of research. Contact him with non-gardening questions by emailing the editor at editor@thevidette.com. Those with gardening questions should contact a WSU Master Gardener volunteer at pnwmg@yahoo.com.