Can potatoes and onions be stored together?

Potatoes and onions are the two items most often put side by side in the kitchen, yet kept together they shorten each other's life. Both want somewhere cool and dark, but they are not suited to sharing the same box.

What happens when they sit side by side?

Onions release moisture and gas while they are stored; potatoes release moisture in the same way. When the two items are together in a closed box, that moisture cannot get out and both stay in an environment damper than it should be.

The result advances in the same direction for both. Potatoes sprout and soften earlier; onions start to soften and smell, beginning with their outer layers. Stored separately, both keep noticeably longer.

This is one of the storage mistakes most easily put right in a kitchen. Two separate boxes or two separate shelves cost nothing extra, and once set up they work on their own.

Where should potatoes sit?

Potatoes should sit somewhere cool, dark and ventilated. A potato exposed to light turns green; it is not enough to cut the greened parts away and be done with it, this change means the potato has to be gone over completely.

A closed plastic bag is the least suitable way of storing them. The moisture building up inside cannot escape, and the potato both sprouts quickly and starts softening at the surface. A perforated box, a net or a cloth bag is far more suitable.

The fridge is not a preferred place for potatoes either. The starch structure inside a potato kept in the cold changes; when cooked, its taste and color come out different from what you expect, and that change cannot be undone.

Where should onions sit?

Onions want somewhere cool but dry, and ventilation matters for them even more than for potatoes. A hanging net or an open basket are the ways onions keep longest.

Onions do not keep well in the fridge either. The damp of the fridge softens the outer layers of the onion and a wetness forms on the surface; that wetness turns into spoilage before long and the smell spreads through the whole fridge.

Cut onion is the exception to this. Once cut, an onion must be stored in a closed container and in the fridge; a cut onion left out both dries and passes its smell to everything around it.

Where else does the same logic hold?

Some fruits and vegetables release a gas that speeds up ripening while they are stored. So when certain items sit side by side, one speeds up the ripening of the other and both have shorter lives.

Bananas, apples and pears are the most common items in this group. Keeping them in a separate bowl from the other fruit keeps both them and their neighbors usable for longer.

Garlic should sit apart from potatoes and onions too. All three are usually gathered in the same corner, but each wants a different level of humidity; kept in separate containers, all three last longer.

How do you set the kitchen up?

The most practical answer is to set aside a single shelf for these items and use separate containers on that shelf. Whether the containers are open or perforated is the single most decisive detail.

The position of the shelf is worth thinking about too. The cupboard above the stove and the oven is the hottest place in the kitchen; potatoes and onions put there spoil far earlier than the ones on a cool shelf in the same house.

Being visible is what gets them used. A potato in a closed box at the bottom of a cupboard is forgotten; a potato in an open basket enters the week's cooking decisions on its own.

What about the ones starting to spoil?

The sprouts on a slightly sprouted potato can be picked off and the potato used; but ones that have softened, shrivelled or greened fall outside that and are not used.

With onions, the outer layers drying is not a problem; these are peeled off and thrown away and the inside is used. But an onion that has softened, become wet or changed in smell is not judged the same way.

Making that distinction regularly extends the life of the remaining items too. A single onion starting to spoil speeds up the spoiling of the others in the same basket, and a weekly check prevents that.