Of course, all foods last for a shorter period of time if they are not stored properly. But remember, potatoes, unlike a lot of other fresh vegetables, may have a sell by date if they are sold in a plastic bag. This is the last day they may be sold, not consumed. Because of this distinction, you may safely use potatoes to compliment your favorite meals even after the sell by date has lapsed. If there is no date, like most fresh vegetables, then the date to use for the table is the purchased date.
How to tell if Potatoes are bad, rotten or spoiled?
Practicing proper hygiene and food safety techniques will help prevent foodborne illness.
Some common traits of bad potatoes are discoloration and growths through the skin. The potatoes will begin to get soft and wither. Potatoes are still alive when picked, so if potatoes are kept too long in a humid climate they will eventually begin to form new white sprouts. These can be cut off and the potato still used, but the quality of the potato is diminished and you're better off planting the new sprout!
They can also develop green spots is they are exposed to direct light for an extended amount of time, in which case the green spot may be cut off and the rest of the potato may be used.
If the potatoes get wet at all they can also grow mold, in which case they must be thrown out. So, do not wash them prior to storage.
For mashed potatoes, they are starting to get old when the liquid begins to separate from the solid. At first the liquid is fairly clear and can be mixed back in and used, but then the liquid will form a white haze and the potatoes will smell sour - at which point you need to toss the mashed potatoes.
There are, of course, certain health risks associated with spoiled foods, so always remember to practice food safety and enjoy your foods before their shelf life has expired.
How to store Potatoes to extend their shelf life?
Proper food storage is key to extending the expiration date of food.
Potatoes are best stored in a cool dark place. Ideally, potatoes should be stored in a cellar, where they can remain for several months at a temperature of 45°F to 50°F. Keeping them at a higher temperature will cause them to shrink and sprout, especially if there is also low humidity. This is because the potato is composed of 80% water, so it evaporates in a hot, dry climate.
Keeping them at a lower temperature, like the fridge, will cause the potato starch to convert to sugar which makes a sweet taste but also causes them to darken very fast when frying. This process can be reversed by leaving them out of the fridge for 7-10 days. 
Once raw potatoes are cut open they oxidize rather quickly, this can be temporarily eliminated by putting them directly into a pan of salted water as they are cut.
Once prepared, potatoes should be stored in a tightly closed container to keep out moisture and other contaminants.
Raw potatoes do not freeze well, but french fries are made for the freezer. The best form to freeze is the partially cooked french fry. Although freezing is an indefinite form of storage, potatoes are moist and form ice crystals that eventually take over the bag of french fries.
Some benefits of proper food storage include eating healthier, cutting food costs and helping the environment by avoiding waste.
Interesting facts about Potatoes:
How to use extra before your Potatoes go bad?
Last nights dinner can easily become todays breakfast and leftover mashed potatoes are the perfect ingredient for potato pancakes. Add an egg or two (depending on how many mashed potatoes you have left over), salt and pepper and maybe a splash of milk if your potatoes are too thick. Whip the mixture up with a fork and then, when your pan is hot and oiled on medium high heat, put a scoop of potato mixture into the pan and flatten with a spatula. Turn when browned, brown the other side and you've got easy potato pancakes.
How long are Potatoes good for when prepared in a dish?
How long do potatoes last? That depends. How long does butter last? In general, potatoes last only as long as the quickest expiring ingredient in the dish.
What are our shelf life resources?
In determining how long Potatoes lasts, our content incorporates research from multiple resources, including the United States Department of Agriculture and the United States Food & Drug Administration. In addition, we scoured the web for informative articles and reports related to food safety, food storage and the shelf life of Potatoes.
*An important note about expiration dates...
Although the Potatoes shelf life information on Eat By Date is generally reliable, please remember that individual cases will vary and that our advice should only be taken as an opinion and not a replacement for your health care prefessional. Please eat responsibly!