Onion

The kitchen's foundation crop - and the one where day length is everything: match long-, intermediate-, or short-day varieties to your latitude or you'll harvest scallions instead of bulbs.

Choose the right day-length type for your latitude, start from seed indoors or transplants/sets, and get them in early for a long leaf-building season.

First choose the day-length type for your latitude - this is the single most important onion decision (see Climate). Then pick a starting method. From seed (the widest variety choice and best storage) sow indoors 8-12 weeks before transplanting; onions are slow. Transplants (bareroot bunches) are the easy middle path. Sets (little dormant bulbs) are the simplest but offer fewer varieties and bolt more readily.

Get onions out early - they're cold-tolerant and every day of cool-season leaf growth before bulbing means a bigger bulb, because each leaf becomes a bulb ring. Space 4 inches apart in rich, loose, well-drained soil in full sun; plant transplants shallow (about an inch deep). Keep the bed weeded from day one - onions have weak roots and won't out-compete weeds.

Feed nitrogen and weed hard through leaf growth, then stop feeding and taper water once bulbs swell.

An onion's whole life is a race to build leaves before day length triggers bulbing, so the leaf-growth phase is where care counts. Feed nitrogen regularly (blood meal, fish emulsion, or a balanced fertilizer) from establishment until bulbing begins - more leaves mean more, larger rings. Keep the bed relentlessly and shallowly weeded, and water evenly, about an inch a week; onions can't make up for growth lost to weeds, drought, or hunger.

Then flip the switch. Once bulbs start to swell, stop feeding - late nitrogen delays maturity, thickens necks, and ruins storage. Taper off watering as the tops begin to soften and fall, so the bulbs cure dry in the ground. Don't fold the tops over by hand to hasten harvest (an old myth that just bruises them); let them flop on their own.

Lift when half the tops have fallen, then cure 2-4 weeks in a dry airy place until the necks are papery.

Onions tell you when they're ready: when about half or more of the tops have naturally bent and flopped over at the neck, bulbing is finished. On a dry day, loosen the soil with a fork and lift the bulbs (don't yank by the tops). Any that bolted - sent up a flower stalk - won't store, so eat those first.

Then cure, the step that determines whether they keep for weeks or months. Spread the whole plants, tops on, in a single layer somewhere warm, dry, shaded, and breezy for two to four weeks, until the necks are completely papery-dry and tight and the outer skins are crackly. Only then trim the tops to an inch and the roots close, brush off soil (don't wash), and store. A soft or thick neck is the sign a bulb won't keep.

Cool, dark, dry, and airy: well-cured storage onions keep 3-8 months; sweet onions only weeks. Never a sealed bag.

Storage life depends on both the variety and the cure. Well-cured storage onions (pungent yellow and red keepers like Copra, Patterson, Yellow Globe) hold 3-8 months in a cool, dark, dry place with airflow - mesh bags, slatted crates, or braided tops hung up. Sweet onions (Vidalia/Granex types, Walla Walla) have high water and sugar and keep only a few weeks to a couple of months; eat those first.

Never store onions in a sealed plastic bag (trapped moisture rots them) or next to potatoes (each hastens the other's spoilage). Keep them cool but not in the fridge unless already cut. Sprouting, soft spots, a strong smell, or mold at the neck mean a bulb is going - use it now. Chop-and-freeze or dehydrate the surplus.

Day length is the whole game: long-day onions north of the 36th parallel, short-day in the South (fall-planted), intermediate in between.

Everything about growing onions comes down to matching the variety to your latitude, because day length triggers bulbing. North of about the 36th parallel (roughly zones 3-6, the northern US and Canada): grow long-day onions, which bulb when days reach 14-16 hours in early-mid summer; start them early for maximum leaf growth first. South of the 36th parallel (roughly zones 8-11, the southern US): grow short-day onions, which bulb at just 10-12 hours - plant them in fall to grow over the mild winter and bulb in spring (spring-planted short-days bulb too soon to size up). The transition band around the 36th parallel (roughly zone 7): intermediate/day-neutral types are safest and adapt across the widest range. Plant a long-day onion in the Deep South and it never gets enough daylight to bulb; plant a short-day onion up north and it bulbs while still tiny. This one choice makes or breaks the crop.

Tiny bulbs usually mean the wrong day-length type or weed/nutrient starvation; thick necks and rot mean poor curing; bolting follows a cold spell.

Big tops but tiny bulbs (or no bulb): most often the wrong day-length type for your latitude, or the plant never built enough leaves - weeds, drought, poor soil, or too-late planting. Match the variety and grow leaves hard early. Bolting (a flower stalk): triggered when young plants hit a cold spell after warmth (common with oversized sets); pull and use those bulbs first, they won't store. Thick, soft necks and bulbs rotting in storage: under-curing, or too much late nitrogen and water - cure fully and stop feeding at bulbing. Silvery streaks and stippling on leaves: thrips in hot dry weather. Bulbs rotting in wet ground: poor drainage; onions demand it. Yellowing, wilting plants that pull up easily with white fungus: white rot, a permanent soil problem - see Threats.

Small servings, real chemistry: vitamin C, B6, and the organosulfur and quercetin compounds behind the health research.

Nobody eats onions by the bowlful, but they carry real nutrition at seasoning quantities: vitamin C, vitamin B6, folate, potassium, and fiber, especially the prebiotic fibers (inulin and fructans) that feed beneficial gut bacteria. Their signature compounds are the organosulfur molecules released when you cut them (the same ones that make you cry) and the flavonoid quercetin, concentrated in red and yellow skins.

Those compounds are why onions show up in cardiovascular, anti-inflammatory, and blood-sugar research - as part of a diet, not as a drug. Red onions carry the most quercetin and anthocyanins; sweet onions the least pungency and sulfur. Cooking mellows the sharp compounds but keeps most of the quercetin. Grow them for flavor; the health benefits ride along.

The universal base - sweated for foundation, caramelized for sweetness, raw for bite, grilled or pickled - plus green tops as scallions.

The onion is the most-used aromatic on earth, and it's really several ingredients depending on treatment. Sweated gently in fat, it's the soft, savory foundation under countless soups, sauces, and braises. Caramelized slowly to deep brown, it turns jammy-sweet for burgers, tarts, and French onion soup. Raw (best from sweet or red onions, or soaked in cold water to tame the bite), it's the crunch in salads, salsas, and sandwiches. Grilled or roasted whole, it mellows into sweetness.

Match the type to the job: pungent yellow storage onions for cooking, mild sweet onions (Vidalia, Walla Walla) for raw and roasting, red onions for color and salads and pickling (quick-pickled red onion is a bright universal topping). And don't forget the green tops - thinnings and young plants are scallions, and even a bolted onion's hollow stalk can be snipped as garnish.

Biennial like garlic's cousin: let a bulb overwinter and flower in year two for seed, or multiply the easy way from sets.

Onions flower and set seed in their second year, so seed-saving means replanting a few of your best cured bulbs the following spring (or leaving them in the ground in mild zones). In year two each bulb sends up a tall stalk topped with a globe of small white flowers that yields hundreds of black seeds. Cut the heads when the seed shows, dry them, and rub the seed out - but note the catch: onion seed is short-lived, viable only about a year, so save it fresh and sow it the next season, never stockpile it.

Onions are insect-pollinated and cross with other flowering onions nearby, so isolate for pure seed, and save from open-pollinated (not hybrid) types. The easier multiplication route is sets - small bulbs grown from a dense seeding one year and replanted the next - which is how sets are commercially produced and how you can perpetuate a variety without the two-year seed cycle.

A long, respectable folk-medicine record with modern support for modest cardiovascular and anti-inflammatory effects - as food.

This section records how people have traditionally used this plant, and what is known about the risks. It is history and general information — not medical advice, and not a recommendation to treat anything. Plants are not dosed like medicines, some interact with prescriptions, and some are harmful in ways that are not obvious. Talk to a clinician before using any plant medicinally.

Onions, like their cousin garlic, have one of the oldest and best-documented places in traditional medicine - used across ancient Egypt, Greece, India, and China for infections, coughs, wounds, and heart complaints, and the folk 'onion poultice' or onion-and-honey cough syrup persists to this day. The modern evidence is respectable if modest: the organosulfur compounds and quercetin show anti-inflammatory, antioxidant, and mild cardiovascular effects in studies, and the prebiotic fibers genuinely support gut health.

As with most kitchen medicine, keep it honest - these are the gentle benefits of eating onions regularly, not a treatment, and the strongest effects come from raw or lightly cooked onion where the sulfur compounds survive. The onion earns its folklore better than most: a food that quietly supports health, best taken by the plateful in cooking rather than the spoonful as a remedy.

One of humanity's oldest crops - a pyramid-builder ration and a symbol of eternity in Egypt - now grown on every inhabited continent.

The onion is among the oldest cultivated plants, grown for at least 5,000 years and probably domesticated in Central Asia. It was central to ancient Egypt, where its concentric rings symbolized eternity, onions were painted in tombs and buried with pharaohs, and (with garlic and radishes) they reportedly fed the laborers who built the pyramids. Greeks, Romans, and every civilization since prized the onion for keeping well, traveling far, and flavoring everything.

Because it stores and ships so well, the onion spread across the entire world early and became a base ingredient of virtually every cuisine - one of the few crops with no regional cuisine that doesn't use it. Today it's grown on every inhabited continent, in the same day-length-matched way home gardeners still puzzle over: long-day in the north, short-day in the south, an ancient crop still governed by the sun.