Most people buy potatoes from the supermarket ready packed in those plastic bags. And before they've finished the bag, they have to throw it out because the potatoes have either gone green and sprouted, or they've started to rot.
Here is how to store potatoes so they keep safely for much longer.
Potatoes need dark dry conditions to keep well. All fruit and veg expirate water vapour, and potatoes are no exception - and if they're stored in a plastic bag, the water vapour condenses on the side on the bag, and the water then drips onto the potatoes. This is a signal for bacteria and fungi to get to work and rot the potatoes.
The other mistake people make is to put them in the refrigerator - again the slightly wet conditions of the fridge will cause water to condense on the skin of the potatoes and start the rotting process.
Don't keep them in a bright corner of your kitchen either - light will turn the potatoes green and cause them to sprout.
So the first thing to do is remove them from their plastic bag. Get a cardboard shoe box (or any other type of cardboard box with a lid), and punch holes all over it (in the sides, the bottom and in the lid). The holes are there to let the air circulate and keep the box dry. Just use a screwdriver or ball-point pen and make the holes in the cardboard from the inside out.
Then place your potatoes in the box after inspecting them - throw away any that have a soft spot as these have already started to rot, and throw away any that have mold. Then keep the box in a cool dry part of your house - a garage or a dark shelf that doesn't get any sunlight.
Keep the potatoes away from other produce - for some unknown reason, the presence of onions, bananas and other veg seems to trigger the potatoes into spouting.
As long as you keep them cool, dry and dark the potatoes should keep for about four months.