Allium Cepa
Onion / Ui / Zwiebel / Oignon
When to buy // How to store // Impact // What's in it for you // Best way to prepare // Grow your own // Origin & History // Sources
When to buy
Onions are available year-round in the Netherlands, but there's a seasonal split worth knowing.
The main harvest, from seed-grown bulb onions (zaaiuien), happens in August and September, with the outer skin drying into the papery layer that protects the bulb through months of storage, which is what makes onions a practical, low-food-miles choice through most of the year.
A smaller, earlier crop (winteruien) is sown the previous autumn and harvested from mid-June, giving a genuinely fresh onion well before the main harvest comes in, though it doesn't store as long. (source)
Either way, imported onions are the exception for most of the year rather than the rule.
The main harvest, from seed-grown bulb onions (zaaiuien), happens in August and September, with the outer skin drying into the papery layer that protects the bulb through months of storage, which is what makes onions a practical, low-food-miles choice through most of the year.
A smaller, earlier crop (winteruien) is sown the previous autumn and harvested from mid-June, giving a genuinely fresh onion well before the main harvest comes in, though it doesn't store as long. (source)
Either way, imported onions are the exception for most of the year rather than the rule.
How to store
|
For everyday use, Keep onions dark specifically, since light exposure triggers greening of the outer scales. And keep them ventilated: avoid sealed plastic bags or airtight containers, which trap moisture and speed up mould and softening; a paper bag, mesh bag, or open bowl works far better.
Bought in normal supermarket quantities and used within a week or two, this is genuinely enough: onions don't need cellar-level cold to get you through a typical week of cooking, they just need air circulation and to be out of direct light and heat. Skip the fridge's crisper drawer for whole onions. It's more humid than onions like, and that humidity works against them rather than for them, encouraging softness and mould rather than preventing it. A cool, dry spot outside the fridge holds up better. (source) Keep onions away from other produce. Even whole, uncut onions continuously release volatile sulfur compounds (source), these compounds are absorbed by nearby fruits and vegetables, especially anything porous or fatty, so storing onions in their own separate spot protects their neighbours' flavour. |
Stockpiling a larger quantity
If you're storing a whole harvest, a bulk buy, or want onions to last through winter rather than a couple of weeks, the calculus changes and genuinely cold storage starts to matter. Onions kept close to 0°C with 60-70% humidity can last 6-9 months for pungent storage varieties, compared to just weeks at room temperature. If you're storing onions with their tops still on, from your own harvest or bought directly from a grower, braiding them together before hanging is a traditional way to get excellent airflow around every bulb at once, and it lets you grab one onion at a time without disturbing the rest. This only works if the onions are properly cured first, dried until the necks and outer skins are papery, since skipping that step is the main cause of storage rot regardless of temperature. At home, an unheated garage, shed, or cellar gets closest to these conditions; a heated house rarely does. |
Historical storageBefore refrigeration, onions were typically braided or strung together by their dried leaves and hung, in a barn, cellar, attic, or from rafters indoors, a technique tracing back to pioneer-era farming and still practiced today.
Hanging kept onions off the ground, gave every bulb full airflow on all sides, and kept them out of the damp that caused rot, all without a single piece of equipment. Curing came first and mattered as much as the storage method itself: bulbs were pulled once the tops began to yellow and flop over, then left to dry in a shaded, ventilated spot for one to three weeks, until the outer skins turned papery and the neck tightened. Only cured onions kept well; anything stored too moist rotted quickly regardless of how it was hung. The technique carried real, practical logic that modern food science later confirmed: less moisture at storage time directly extends shelf life, since it's respiration rate, not just temperature, that drives spoilage.
Braiding and stringing weren't just decorative farmhouse tradition, they solved the airflow and moisture problem before anyone had a word for "relative humidity." |
|
Impact at a glance
|
Carbon footprint
Onions carry a genuinely low environmental footprint, among the lighter vegetables you can grow. One life-cycle study put the carbon footprint of growing onions at roughly 0.05kg CO2e per pound at the farm-gate stage, rising to around 0.11kg CO2e per pound once harvesting, processing, and packaging are included, still low compared to most vegetables. (via impactful Ninja) Water footprint Studies (like this one) for onions show a wide variations by region, irrigation method, and season. Dutch production is generally water-efficient and needs less irrigation than warmer, drier growing regions, though supplemental irrigation is still common on sandy Dutch soils during dry spells. Worth noting: some early-season onions sold in Europe are grown in drier growing regions overseas, where the water footprint is much larger. Checking the label with this in mind is well worth it. |
Pesticide Use
Onions consistently rank among the lowest-residue produce available, appearing on the EWG's Clean Fifteen list year after year, with close to 60% of samples showing no detectable pesticide at all. This isn't because little is applied during growing, commercial onion production commonly relies on repeated insecticide and fungicide applications throughout the season to manage pests like thrips and diseases like botrytis leaf blight (source), but most residue breaks down before harvest or stays concentrated in the papery outer skin, which gets peeled away before eating. Within the EU, onions are regularly monitored by EFSA as part of its pesticide control programme, with compliance consistently around 99% in recent years. Food Miles The Netherlands is the world's largest onion exporter by a wide margin: in the 2025-2026 season, Dutch growers exported nearly 1.4 million tonnes to over 130 countries, despite using only 1-2% of the world's onion-growing area (source). For a domestically sold onion, food miles are typically very low. One exception: late-season imports, particularly from the Southern Hemisphere (New Zealand, Chile, Australia), bridge the gap before the new Dutch harvest, so "very low food miles" depends somewhat on when in the season an onion is bought. (WUR) |
What's in it for you
Nutrients
According to FoodData, onions are low in calories and mostly water, around 89% by weight. What's left is mostly carbohydrate, roughly 9g per 100g, largely simple sugars plus fibre, with only trace fat and protein. Nutrient density is moderate to low on standard vitamin/mineral measures (modest vitamin C, B6, folate, potassium), but onions make up for it elsewhere: they're one of the richest everyday sources of quercetin, an antioxidant not captured by those scores at all. Fiber is modest but useful, around 1.7-1.9g per 100g, with a meaningful share as fructans, a prebiotic fibre that feeds gut bacteria. Protein is negligible, under 1g per 100g, and largely missing methionine, one of the essential amino acids. |
BenefitsOnion's most researched benefit is prebiotic: fructans feed beneficial gut bacteria, producing short-chain fatty acids like butyrate through fermentation. A recent lab study confirmed this isn't just theoretical, onion extracts measurably reshape gut microbial communities and boost these beneficial metabolites. Onions are considered a significant everyday source of these fibres, alongside garlic and Jerusalem artichoke, making gut health the clearest, most direct benefit of eating them regularly. Quercetin, the antioxidant onions are best known for, has been studied for cardiovascular and anti-inflammatory effects, with observational studies linking regular allium intake to modest reductions in blood pressure and LDL oxidation. This is a softer claim, though: the strongest clinical evidence comes from concentrated extracts rather than typical servings, and content itself varies by cultivar, growing environment, and storage duration, so two onions can differ meaningfully before they even reach the kitchen. Onions are best described as potentially supportive of heart health rather than proven to lower blood pressure on their own. |
Best way to prepareRaw onion keeps the sulfur compounds linked to anti-platelet effects at their highest, since any cooking leaches them out, and it also protects fructans, the prebiotic fibre behind onion's gut health benefit, which is heat-stable anyway and holds up fine either way. (source) Sautéing or roasting is the winner for quercetin, increasing availability by 7-25% as heat breaks down plant tissue and makes the antioxidant more accessible, while causing only modest loss to the sulfur compounds compared to boiling (source). Boiling loses the most across the board, an 18-30% drop in quercetin and the bulk of the sulfur compounds leach straight into the water. If you do boil, keep the liquid, in soup or stock, most of what's lost ends up there instead of down the drain. |
A note on tearsCutting an onion ruptures cells and releases an enzyme that converts sulfur compounds into a gas called syn-propanethial-S-oxide, its exact biochemical origin only correctly identified in 2002 after decades of assuming a simpler mechanism (source). It's the same class of chemistry that gives onions their pungency, so there's a genuine trade-off between a milder, tear-free onion and a more flavourful one. A 2008 study successfully suppressed the relevant gene in a lab setting, reducing tear-inducing compound activity by up to 1,544-fold and virtually eliminating the tearing response, at some cost to pungency. Separately, commercially available "tearless" onions like Sunions reached the same result through decades of traditional crossbreeding rather than gene suppression, selecting for naturally low volatile-compound levels. |
Stopping yourself from tearing upThe most reliable combination is a sharp knife, a chilled onion, and good ventilation. Enzyme activity, including the one responsible for producing the tear-inducing gas, slows down at lower temperatures, so refrigerating an onion for 30 minutes (or freezing it for 10-15 minutes) genuinely reduces the effect, this follows basic, well-established enzyme kinetics rather than kitchen folklore.
A sharp knife causes less cell rupture than a dull one, so it releases less of the enzyme and irritant compound to begin with, and working near an open window, fan, or extractor hood disperses the gas before it reaches your eyes. Other popular tricks, cutting the root end last, running water, a wet paper towel nearby, are plausible in principle but not well-documented with hard evidence, so treat them as optional extras rather than reliable fixes. |
And the best fix of all? Wearing Goggles. They work through simple physical barrier rather than chemistry, no gas reaching your eyes means no reaction.
Swim goggles tend to seal more tightly than dedicated "onion goggles," for better protection, though at some cost to comfort during longer prep. 
|
Grow your own
Planting & harvestingOnions can be started from seed, sets (small dormant bulbs from the previous year), or transplants; sets are the easiest and most forgiving route for a first-time grower. Plant sets 2-5cm deep and 5-10cm apart, pointy end up, as soon as soil is workable in spring; seeds go slightly shallower, around 0.5-1cm deep. Don't mound soil around the stems the way you would with potatoes, onions push their bulbs upward naturally as they grow, and hilling them can actually encourage stem rot.
Harvest when roughly half the tops have fallen over and dried naturally, this is the reliable maturity signal, not calendar timing. After lifting, cure the bulbs for two to four weeks in a warm, well-ventilated spot until the outer skins are papery and the neck is tight, this step determines how well they'll keep. |
|
Space needed
Rows should sit 30-45cm apart, with bulbs spaced 5-10cm apart within the row for full-size onions (closer, around 5cm, if you're planning to harvest some early as green onions). A modest 2m x 2m bed can comfortably hold several dozen plants. Difficulty: low Onions are genuinely easy and low-maintenance once planted, no hilling, no complex pruning. The main risks are poor drainage (onions dislike wet feet) and inconsistent watering, since water stress directly reduces bulb size. They're also poor competitors against weeds early on, so the first six to eight weeks after planting need reasonably diligent weeding. Want to know more? Here is the complete RHS guide to growing Onions |
Origin & Botanical background
|
The onion, Allium cepa, belongs to the Amaryllidaceae family, forming sub-family Alloideae alongside garlic, leeks, chives, and shallots.
Its origin is genuinely uncertain, the presumed wild ancestor is now extinct or unidentified, so historians and geneticists rely on archaeological and textual evidence rather than a living wild relative. Genetic evidence increasingly points to a gradual, hybridized domestication process across multiple regional lineages rather than a single clean origin point, a pattern that still shows up today in how strongly onion varieties are tied to the day-length and climate of where they were bred (source). Most evidence points to Central Asia, likely in the region spanning modern Iran and western Pakistan, with cultivation stretching back at least 5,000-7,000 years, making it one of humanity's oldest domesticated vegetables. Onions appear extensively in ancient Egyptian iconography, where their concentric rings were seen as a symbol of eternity, and in Mesopotamian cuneiform recipes. |
Variations and sub-species
|
Onions are grouped primarily by colour and pungency rather than starch content the way potatoes are. Yellow onions are the most common all-purpose type, sharp raw, sweet when cooked slowly. Red onions are milder and often eaten raw in salads. White onions are sharper and more pungent, common in Mexican and Southeast Asian cooking.
|
|
Sweet onions (like Vidalia or Walla Walla) are bred and grown for low pungency, but store poorly compared to standard yellow storage onions, precisely because the compounds that make onions pungent are largely the same ones that help them keep. Day-length also matters for growing: onion varieties are split into long-day and short-day types, and planting the wrong type for your latitude results in poor bulb formation regardless of care.
|
