One St. Patrick’s Day when I was a kid, my mother decided to surprise us at dinner by serving mashed potatoes that she had colored green.

My siblings and I managed to get one forkful down but it was challenging. There was something very unappetizing about green mashed potatoes.


Occasionally we find an area of greenish skin on a potato that we purchased or grew ourselves. This area of green skin indicates a substance forming in the potato called solanine, which forms when a potato is exposed to light for an extended period of time.

Solanine is a toxic substance formed to protect the tater tuber from insects and other creatures that may want to eat it. It has a bitter taste and is present in greater concentration in the sprouts. That makes sense since the sprout needs to provide for the growing plant.

There are things we’ve done for years without thinking about why we do them. Do you store potatoes in the dark? Do you remove sprouts from potatoes before cooking? Do you peel or cut out the green spots?

Did you ever stop to think why you do that? I knew the green spots were not good for you but didn’t know why. It’s always a good day when we learn something new.

Note: Don’t give potato peels with green areas to pets either!


Have you ever boiled potatoes and had them turn black? There are very specific reasons for this. If you boil potatoes in an aluminum pan or iron pot, don’t be surprised if they turn black. This is due to a chemical reaction between the pan and the chemicals in the potatoes. Stainless steel, glass, or ceramic are not reactive and your potatoes will not change color.

If a cooked potato is exposed to air while it cools, a blue-gray area that’s about as appetizing as my mother’s green mashed potatoes, may occur. Although it may not look harmless, it is. It’s the exposure to air while the potatoes cool that is responsible. Who thought potatoes could be so complicated?

There is another reason a potato may discolor and blacken when cooked: It might just be the chemical makeup of the potato. Or it may have been dropped while it was cold. (I’m not making this stuff up).

According to the American Journal of Potato Research Jan/Feb 2004: “After-cooking darkening occurs when potatoes are exposed to air after cooking, including boiling, baking, frying, or dehydration. After-cooking darkening has been reported from every potato-growing area in the world and is one of the most widespread, undesirable tuber traits, even though ACD does not affect the flavor or nutritional value of the potatoes.” Who knew?


You might want to start thinking about garlic planting. I am seeing hard neck garlic in nurseries and garden centers. You can use garlic purchased at the market to plant, but be aware it may have been treated to delay sprouting for a longer shelf life.

Where ever you get your garlic, look for strong, healthy cloves to plant. October will be here before you know it. I wasn’t going to mention that, but I had to let folks know when we plant the garlic. My apologies.

Last chance to register for our trip to Montreal Botanical Gardens on September 10. Call us or email me for information.

Jolene Wallace is the consumer horticulture educator for Cornell Cooperative Extension in Clinton County. Contact her at 518-561-7450 or


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