You’ve probably done it. Most people do. You come home from the grocery store with a heavy five-pound bag of russets and a mesh sack of yellow onions, and you shove them both into that dark, cool cabinet under the sink or into a single wicker basket in the pantry. It feels right. They’re both root-adjacent vegetables, they both like the dark, and they’re the twin pillars of almost every savory meal you’ll cook this week. But honestly? You’re accidentally sabotaging your dinner.
If you’ve ever reached into your pantry only to find your potatoes have sprouted weird, alien-looking green limbs or your onions have turned into a mushy, weeping mess, you’ve seen the consequences firsthand. The question of can you store onions and potatoes together isn't just a matter of kitchen organization; it’s a matter of chemistry.
The Science of Why They Hate Each Other
It comes down to gas. Ethylene gas, specifically. Onions are high producers of this naturally occurring ripening agent. While ethylene is great when you want to ripen a hard avocado in a paper bag, it’s a nightmare for a potato. When potatoes are exposed to the ethylene emitted by onions, they wake up. Their internal clock starts ticking faster, signaling the eyes of the potato to sprout.
Once a potato sprouts, it starts converting its starches into sugars. This makes the texture grainy and the flavor off. Even worse, onions release a significant amount of moisture. Potatoes are essentially dormant organisms that are very sensitive to humidity. When you trap that onion-moisture in a confined space with a potato, you aren't just encouraging sprouts; you’re inviting rot.
According to various agricultural extensions, including experts at the University of Idaho (the literal capital of potato knowledge), the ideal storage for these two items is worlds apart. Potatoes need high humidity but plenty of airflow to prevent "damp-off." Onions, conversely, need very low humidity—they want to stay dry and breezy to keep their outer skins papery. Putting them together creates a microclimate that serves neither. The onion gets too damp from the potato's respiration, and the potato gets gassed by the onion. It’s a lose-lose situation.
The Ethylene Factor: A Closer Look
Ethylene is a tiny hydrocarbon gas. $C_{2}H_{4}$. It's invisible, but its effects are dramatic. Most "climacteric" fruits and vegetables use it as a hormone to coordinate ripening. Think about a bunch of bananas—they all turn yellow at roughly the same time because they are signaling to each other.
Onions aren't the only culprits, but they are the most common kitchen roommates for spuds. If you throw an apple or a ripening tomato into that same bin, you’re just pouring gasoline on the fire. Some people think the "onion smell" is what ruins the potatoes, but it’s actually the silent, odorless gas doing the heavy lifting. Interestingly, the University of Maine's Potato Program notes that while cold storage can slow down some of this, the average home pantry is far too warm to mitigate the ethylene effect. Most of us keep our kitchens at 68-72 degrees. At that temperature, the chemical reaction is basically on fast-forward.
Proper Storage: Give Them Some Space
So, if you can’t keep them together, what do you do? You don't need a massive cellar. You just need a bit of distance and the right containers.
The Potato Strategy
Potatoes crave darkness. If they see light, they produce chlorophyll, which turns the skin green. That green isn't just ugly; it’s a sign of solanine, a bitter toxin that can cause an upset stomach in high amounts. You want a cool, dark, well-ventilated spot. A cardboard box with holes poked in it is actually better than a plastic bag. Never, ever store them in the fridge. The cold turns the starch to sugar immediately, which is why "refrigerated" potatoes often turn dark brown or black when you fry them. It's called the Maillard reaction gone wrong.
The Onion Strategy
Onions need to breathe even more than potatoes. They love a hanging mesh bag or a wire basket. They want to be bone-dry. If you keep them in a drawer, make sure it’s not crowded. The only exception to this is "spring onions" or scallions—those belong in the fridge in a jar of water. But for your standard yellow, red, or white cooking onions? Keep them on the opposite side of the kitchen from your potato stash.
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What Most People Get Wrong About the Pantry
We have this mental image of a "root cellar" where everything is tossed together in wooden bins. But old-school cellars were huge. They had natural ventilation and enough cubic footage that the gases couldn't reach high concentrations. Our modern kitchen cabinets are tiny, sealed boxes. In a 2-foot-wide cabinet, the ethylene concentration becomes a concentrated cloud.
I’ve seen people try to use those "dual-chamber" baskets where the onions sit on top and potatoes on the bottom. It looks cute on Pinterest. It’s a disaster in practice. The gas rises. The moisture settles. You're basically building a laboratory for decomposition.
What About Other Roommates?
If you can't put onions and potatoes together, what can they live with?
- Potatoes and Garlic: Generally okay. Garlic doesn't pump out ethylene like onions do, and they both appreciate the same dark, dry-ish conditions.
- Onions and Shallots: Perfect. They are family. They share the same needs.
- Onions and Squash: Bad idea. Most winter squashes (like butternut or acorn) are very sensitive to ethylene and will go soft and mealy if stored near onions.
- Potatoes and Bananas: Absolute catastrophe. Your potatoes will have 3-inch sprouts within a week.
There is one weird trick, though. Some studies suggest that storing potatoes with dried herbs like lavender or even specific essential oils can inhibit sprouting, but for the average home cook, simple separation is the best tool in the shed.
How to Save Sprouting Spuds
If you’ve already messed up and stored them together, don't panic. If the potatoes are still firm and the sprouts are small, just flick them off with your thumb. They are still fine to eat. However, if the potato feels soft, shriveled, or has significant greening under the skin, it’s time for the compost bin.
For the onions, check the neck. If the top of the onion where the stem was feels soft or "squishy," it’s starting to rot from the inside out because of the moisture trapped in the shared bin. A good onion should be hard as a rock.
Actionable Steps for a Better Pantry
Stop the cycle of food waste right now. It's easy.
- Audit your current storage. Take everything out. If they are in the same cupboard, move one of them today. Even moving the onions to a bowl on the counter and keeping potatoes in the dark cupboard is a massive improvement.
- Ditch the plastic. Grocery store bags are the enemy. They trap moisture and gas. Transfer potatoes to a paper bag (leave it open at the top) or a wooden crate.
- Check your temperatures. Avoid storing either near the dishwasher or oven. The heat from these appliances will trigger sprouting and decay faster than anything else. A pantry wall that shares an exterior house wall is usually the coolest spot.
- The "One-Week" Rule. If you absolutely must store them near each other because you live in a tiny studio apartment, only buy what you can eat in seven days. The ethylene damage takes a few days to really kick in; if you cycle through your stock fast enough, the chemistry doesn't have time to ruin your food.
- Use a dedicated bin for onions. A wire mesh basket hanging under a shelf is ideal. It keeps them away from other produce and ensures 360-degree airflow.
By simply separating these two kitchen staples, you'll likely double the shelf life of your produce. You’ll save money, reduce waste, and your roasted potatoes will actually taste like potatoes instead of sweet, grainy disappointment.