Cool, dark, dry and airy for both, but never in the same bin. It is not about gases, it is about damp: potatoes want humid air and onions want dry air, so stored together the potatoes' moisture rots the onions while the onions' dryness shrivels the potatoes.
What to check
🌱
Keep potatoes out of the fridge. Cold turns their starch to sugar, which makes them taste oddly sweet and brown too dark when roasted or fried. That is a quality problem, not a safety one.
🌱
Store both in something that breathes: a paper bag, a basket, a slatted crate. Never a sealed plastic bag.
📦
Check the boxon onions, squeeze the neck rather than the body. A properly cured onion has a tight, thin, dry neck and papery skin that rustles. A thick, soft or damp neck means it was not cured well and it will rot from the top down, usually inside the skin where you cannot see it.
⚠️
Green patchesthe green itself is chlorophyll and is harmless, but it forms under the same light that raises solanine, a bitter compound that can upset your stomach in quantity. Solanine sits in the skin, just under it, and in the sprouts and eyes, and cooking does not destroy it. Peel the green away generously and cut out the eyes, or bin the potato if the green runs deep. If a cooked potato tastes bitter or burns the back of your throat, stop eating it.
📝
Notesweet onions like Vidalia and Walla Walla are high-water and do not store. Weeks, not months. They are the one onion worth keeping cool and spread out so they are not touching.
📝
Notesweet potatoes are a different vegetable and want it warmer, around 55 to 60F. The fridge ruins them faster than it does regular potatoes.
Common mistakekeeping potatoes somewhere bright. Light is what turns them green, and it does it faster than age does.
Two things worth knowing at the shelf. For most of the year the potato you are buying was dug the previous fall and held in climate-controlled storage, which is normal. New potatoes are the exception: freshly dug, with skin that scuffs off under your thumb. They do not store, so eat them within a week, and they are the best boiling and salad potato of the year. And variety decides the job: russets are floury, so they bake, mash and fry, while red and white are waxy and hold their shape for boiling and roasting. Gluey mashed potato is almost always a waxy potato in a starchy job.
Buying the big bag: it is cheaper per pound but you cannot inspect it, so hold it up, look at the bottom corners for damp or a dark stain, and smell it. One rotten potato in there will take the bag inside a week.
Written by the team behind RIPE, a free app that reads a photo of the whole produce pile and rings the ripest ones. Every cue above is one you can check with your own hands, and it all works with no app at all.
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The whole bin, in one photo.
You just read the cue for one piece. RIPE reads a photo of the entire display, draws numbered rings on the ones worth taking, and tells you why in the same plain words these guides use. Then it remembers what you brought home and nudges you before it turns.
It claims only what a camera can actually see. Every verdict ends by handing the last check back to your hands, which is the part these guides just taught you.
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