Why storing onions and potatoes together makes both go bad faster, food scientists say

The basket looked so practical: onions on one side, potatoes on the other, tucked under the kitchen counter like they were meant to live there. It felt sensible, even virtuous - no plastic, no fridge space wasted, just two “keep in a cool dark place” vegetables sharing a home. Then, a couple of weeks later, the onions had collapsed into mush and the potatoes were sprouting like mad.

Somewhere between the recipe blogs and the supermarket shelves, a quiet myth settled in: that “root veg” all belong together. Food scientists are now politely insisting the opposite. Put onions and potatoes in the same corner and you’re essentially speeding up their ageing process.

Why onions and potatoes seem like natural roommates

On paper, the pairing sounds reasonable. Both like darkness. Both dislike heat. Neither belongs in the fruit bowl. So they end up side by side in countless cupboards, crates and pantry drawers, usually without much thought.

Many of us grew up watching parents toss a net of onions and a sack of potatoes into the same under‑stairs cupboard. No one explained the logic; it just looked like good housekeeping. When a few potatoes sprouted or an onion went soft, it felt like normal waste rather than a consequence of the storage system itself.

“We treat them as one category - ‘things that last ages’ - and forget they’re living, breathing plant parts with their own chemistry,” notes one food technologist.

The problem is not the box or the darkness. It is what the vegetables quietly release into that shared air.

The invisible gas that makes them age in fast‑forward

Onions and potatoes communicate, in a sense, using gases. As they age, they release compounds that act like tiny signals for ripening, sprouting and decay. Put the wrong signals together and you get a feedback loop that shortens shelf life.

Onions, especially when stored warm or crowded, emit ethylene, a plant hormone that promotes ripening and senescence in many crops. Potatoes do not love ethylene. Expose them to it and they tend to:

• Sprout earlier and more vigorously.
• Develop softer textures faster.
• See certain storage disorders, like internal browning, appear sooner.

Potatoes, for their part, respire slowly and release moisture. In a confined container, that extra humidity wraps around onions, softening their dry outer skins and making them more vulnerable to moulds and bacteria. The crisp, papery jacket that should keep an onion safe becomes damp and patchy instead.

Two quiet processes - onion ethylene and potato moisture - collide in one small space and tip both vegetables out of their comfort zone.

The result is subtle at first: a few eyes on the potatoes, a faint smell from one onion. Leave them together and it turns into a full‑scale spoilage chain reaction.

What actually happens when you store them together

In storage trials, mixed onion–potato crates often show the same pattern. First, potatoes sprout sooner than identical batches kept away from onions. Sprouting is more than a cosmetic issue: it consumes the potato’s starch reserves, so the flesh becomes sweeter and less firm.

At the same time, onions exposed to the slightly damper conditions around potatoes are more likely to:

• Develop soft, watery spots.
• Grow green or black mould at the neck or base.
• Split or collapse from the inside out.

Because both crops are alive, their responses amplify each other. A rotting onion raises local humidity and may release more volatile compounds. Those compounds stress nearby potatoes, which sprout and sometimes develop small rot spots themselves. One failing veg becomes a catalyst rather than a lone casualty.

This is why a basket that looked fine last Sunday can smell sour by the next. The damage is not random bad luck; it is chemistry and biology doing exactly what they are wired to do, just in the wrong combination.

How to store them instead, according to food scientists

The fix is not complicated, but it does mean rethinking the classic “all in one tub” approach. Food scientists and post‑harvest specialists tend to repeat a short list of rules.

Give each crop its own zone

Keep onions and potatoes at least a few feet apart if you can, ideally in separate ventilated containers. They do not have to be in different rooms, but they should not share close, stagnant air.

• Store potatoes in a dark, cool, well‑ventilated spot, ideally between 7–10°C, in a breathable bag or crate.
• Store onions in a slightly drier place, also cool and dark, but with extra airflow - mesh bags, racks or hanging nets work well.

Avoid tightly sealed plastic for either crop. It traps moisture and accelerates rot, even if they are stored separately.

Watch for the chain‑reaction starters

One bruised onion or a cut potato can quietly ruin the whole batch. Check both regularly, take out anything soft, mouldy or visibly damaged, and use it straight away if it is still safe, or discard it if not.

This small habit matters more than the specific cupboard you choose. Break the chain at the first weak link and you extend the usable life of everything around it.

Think about light as well as temperature

Potatoes exposed to light turn green and produce solanine, a bitter, potentially toxic compound. Onions do not have the same problem, but they can sprout if kept too warm or in bright spots. Darkness slows both issues, but humidity and gas exchanges still differ, which is why separation remains key.

Crop	Likes	Hates
Potatoes	Cool, dark, slightly humid air	Ethylene from onions, strong light, sealed plastic
Onions	Cool, dark, dry and well‑ventilated air	Excess moisture, cramped containers, proximity to potatoes

Even a small flat can be organised around these preferences: potatoes in a covered box near the coolest floor area, onions hanging in a mesh bag higher up where air circulates more freely.

Why this tiny kitchen tweak matters more than it seems

For most households, waste hides in slow dribbles. A couple of sprouted potatoes here, a collapsed onion there. It never feels like much. Yet over a year, those small losses add up to kilos of food and a noticeable slice of your grocery budget.

Separating onions and potatoes does not feel glamorous. It will not go viral on social media in the way a clever leftover recipe might. But it sits in the same quiet category as labelling freezer tubs or rotating tins: a small, unshowy habit that reduces waste before you have to get creative.

It also shifts how we think about “long‑life” foods. Even sturdy crops are sensitive to the company they keep. Treating your cupboard like a mini‑storeroom rather than a catch‑all basket helps everything last closer to its full potential.

The reward is simple: fewer mystery smells, fewer slimy surprises, and more evenings where the onion and potatoes you thought you had are actually still usable.

In a cost‑of‑living squeeze, those calm, uneventful moments when food simply behaves as expected are worth more than they look.

Key points at a glance

Point	Detail
Do not mix onions and potatoes	Onions release ethylene; potatoes add humidity. Together they speed each other’s sprouting and rotting.
Separate, cool, dark storage works best	Give each crop its own ventilated container and keep them a short distance apart.
Early checks prevent chain reactions	Remove bruised or mouldy pieces quickly to protect the rest of the batch.

FAQ:

• Can I ever store onions and potatoes together for a short time? For a day or two after shopping, it is not catastrophic, especially in a cool, airy place. Problems arise with weeks‑long storage in the same confined basket or cupboard.
• Do red, white and yellow onions behave differently with potatoes? Their colours and flavours vary, but their storage biology is similar. All standard bulb onions are better kept away from potatoes.
• Is the fridge a safe compromise for both? Potatoes generally do poorly in the fridge; the cold can alter their starch and lead to off flavours when cooked. Onions can go in the fridge once cut, but whole bulbs usually keep better in a cool, dry cupboard.
• What about other vegetables - can they sit with onions or potatoes? Hardy roots like carrots or beetroot tolerate being near potatoes better than onions do, but strong ethylene producers, such as some fruits, are best kept away from both.
• My potatoes are already sprouting. Are they unsafe? Small, fresh sprouts can be cut off and discarded, and the firm flesh used promptly. If large areas are green, bitter or soft, it is safer to bin the potato.