Potato Onion

The onion you never buy twice: plant one bulb, harvest a nest of six, and replant from your own stock forever. Grown on the garlic calendar and the best-keeping onion in the garden.

Plant bulbs shallow in fall on the garlic calendar. The one rule that decides your crop: small bulbs make a few big onions, large bulbs make a nest of many small ones.

Learn the size rule first, because it governs everything. A small bulb — under about an inch and a half across — puts its energy into growing, and gives you a few large onions. A large bulb divides hard and gives you a nest of many small ones. Neither result is a failure; they are two different jobs. Most gardeners deliberately plant a mix: small bulbs for the kitchen crop, large bulbs to multiply their planting stock.

Plant in fall, on the same calendar as garlic, in full sun and loose, well-drained ground. Set each bulb root-end down with the tip at or just under the surface — about an inch deep, a little deeper in the coldest zones — and space them 6 to 8 inches apart so the cluster has room to swell. Water in once, then mulch four to six inches deep with straw or shredded leaves. In zones 3 and 4, fall planting is a gamble even under mulch, so plant in earliest spring instead, or split your stock and try both. That is the whole establishment job; the rest of the year is weeding.

Feed nitrogen and weed hard through spring leaf growth, then stop feeding and taper water as the cluster sizes up. Do not disturb the nest while it divides.

Spring is where the crop is made. Pull the mulch back a little as growth starts, then feed lightly with nitrogen two or three times through leaf growth — every leaf the plant builds becomes bulb. Weed shallowly and relentlessly, because onions of every kind lose badly to competition and cannot make the growth up later, and water around an inch a week. Underground, the mother bulb is quietly splitting into a cluster; leave it alone, do not thin it, and resist scraping the soil away to check on it.

Then flip the switch, exactly as with a common onion. Once the bulbs start to swell, stop feeding. Late nitrogen gives you thick, soft necks, and a thick neck is the surest sign of a bulb that will rot in the basket rather than keep until spring. Taper the water off as the necks soften and the tops begin to lean, so the nest finishes dry in the ground. If a cluster throws a flower stalk (uncommon, and usually after a cold snap), mark it — it will not store, so eat it first.

Lift the whole nest when most tops have fallen, cure it 2-3 weeks until the necks are papery, and set next year's planting stock aside before you start eating.

The plants tell you when: once about half to three-quarters of the tops have bent over at the neck, the cluster has finished sizing. Pick a dry day, loosen underneath with a fork, and lift each nest whole rather than pulling by the tops. Do not fold the tops over by hand to force the issue — that old trick just bruises necks and costs you storage life.

Then cure, which is the step that decides whether these keep for weeks or for most of a year. Spread the clusters in a single layer with the tops still attached, somewhere warm, dry, shaded and breezy, for two to three weeks — until necks are completely papery and tight and the outer skins crackle. Only then break the nest apart, trim tops to an inch and roots close, and brush off the soil without washing. Do one more thing before the basket reaches the kitchen: set your planting stock aside and label it. There is no packet to reorder from, and the best bulbs are always the ones you most want to eat.

Cool, dark, dry and airy: well-cured potato onions keep 8-12 months, the longest of any onion. Never a sealed bag, never beside potatoes.

This is what the crop is for. Properly cured potato onions are the best keepers in the onion family — commonly eight months, often a full twelve, which carries a household from one harvest to the next. Store them cool, dark, dry and with airflow: mesh bags, slatted crates, open baskets, or braided tops hung in a cool room. Check the basket every few weeks and pull anything soft.

The rules are the same as for any onion and worth repeating. Never seal them in plastic — trapped moisture is the fastest route to rot. Do not store them next to potatoes, since each speeds the other's spoilage. Keep them out of the fridge unless already cut. Sprouting, soft shoulders, a strong smell or mold at the neck all mean a bulb is going — use it now. And remember that some of what is in the basket is next year's crop, so keep the planting stock in its own labeled container where nobody grabs it for dinner.

A true onion, not a shallot: pungent, firm, and used anywhere a yellow onion goes. Small bulbs roast whole beautifully.

Despite sharing a botanical group with the shallot, a potato onion cooks like an onion. It is firm, dense and pungent — often sharper raw than a supermarket yellow — and it goes anywhere a cooking onion goes: sweated as the base of a soup or braise, caramelized slowly to jam, sliced into a stew, or fried. The pungency mellows completely with cooking, and the dense flesh holds its shape better than a watery sweet onion does.

The small bulbs from a large mother are their own treat. Peel them and roast them whole alongside meat or potatoes, where they go soft and sweet; drop them into a stew or a boeuf bourguignon in place of pearl onions; or pickle them. The green tops in spring can be snipped like scallions, though every leaf you take costs you bulb size, so take them only from a cluster you have already decided to eat young. Being an heirloom kept for storage rather than for the shelf, the flavor is stronger and more onion-like than most modern hybrids, which is exactly why cooks who find it tend to keep it.

Bulb to bulb, forever: replant from your own cured harvest. Potato onions almost never flower, so there is no seed and no seed packet - your stock is the variety.

Propagation is the crop. Potato onions almost never flower and set little or no viable seed, so every bulb in existence is a division of another bulb, and the way you keep a variety is simply by replanting it. Each fall, take a share of your cured harvest and put it back in the ground: small bulbs if you want big onions next year, large bulbs if you want to multiply your stock fastest. A modest first-year purchase of a pound or two of bulbs, replanted faithfully, becomes a self-sustaining supply within a couple of seasons.

That also means the health of your stock is entirely your responsibility. Only replant firm, clean, well-cured bulbs from clusters that grew well; never replant from a plant that wilted, rotted or bolted. Buy new stock only from a reputable source, and be cautious about accepting bulbs from a garden where alliums have collapsed — white rot travels on planting stock and stays in soil for decades. Keep the replant bulbs labeled and stored separately from the kitchen basket, because the temptation to eat the best ones is real and there is no packet to fall back on.

Zones 3-10 with the calendar shifted: fall-planted across most of the country, spring-planted in the far north, and winter-grown in the warm South.

The potato onion sidesteps most of the day-length trap that governs seed onions. Because you plant a bulb that already carries its own energy, and grow it over the cool season on the garlic calendar rather than raising it from seed through summer, the classic long-day / short-day disaster is far less likely — the standard yellow potato onion has a long record of performing from the upper Midwest to the Gulf. What changes by region is the calendar. Zones 3-4: plant in earliest spring; fall planting works only under a heavy mulch and still loses bulbs in an open winter, so split your stock the first year and see which suits your ground. Zones 5-8: the sweet spot — fall plant on the garlic calendar, mulch, and harvest in early to midsummer. Zones 9-10: plant in late fall and grow through the mild winter for a late-spring harvest; drainage matters far more than cold, and summer heat is the off-season. Everywhere, well-drained ground matters more than anything else on this list.

Nothing but small bulbs usually means you planted a large mother bulb; one or two big ones means you planted a small one. Both are the size rule working.

A nest of nothing but small bulbs: most often you planted a large mother bulb, which is exactly what large bulbs do — plant smaller ones next time. If the bulbs are also thin and pale, suspect crowding, weeds, or hunger in spring instead. Only one or two bulbs, but big: you planted a small bulb, and that is the rule working correctly. Whole crop small: weed competition, drought during spring leaf growth, or too-late planting — the crop is made before bulbing starts. A flower stalk (bolting): triggered by a cold spell after warmth; those clusters will not store, so eat them first. Thick soft necks and bulbs rotting in the basket: under-curing, or too much late nitrogen and water. Nothing came up after fall planting: either winter kill in a cold zone with too little mulch, or bulbs set upside down — the root end goes down. Yellowing, wilting plants that lift out easily with white fuzz and black specks at the base: white rot — see Threats, and do not move bulbs or soil out of that bed.

An heirloom that nearly disappeared: a staple of nineteenth-century American kitchen gardens, kept alive by seed savers after commerce abandoned a crop that comes with no seed to sell.

Multiplier onions are very old — bulb-propagated onions were grown across Europe and the Near East long before graded seed existed — and the potato onion arrived in North America with European settlers. Through the nineteenth century it was a fixture of American kitchen gardens, valued precisely because it needed no seed and stored until the next harvest. Nineteenth-century seed catalogs listed it routinely, and in the Appalachian and Southern gardens where it was best loved it was known simply as the hill onion or mother onion.

Then it nearly vanished. A crop propagated by bulb offers a seed company almost nothing to sell, and as commercial hybrid onion seed took over in the twentieth century the potato onion fell out of catalogs and out of memory. What saved it was exactly the habit that made it uncommercial: gardeners kept replanting their own stock and passing bulbs along. Heirloom seed-saver organizations — the Seed Savers Exchange and Southern Exposure Seed Exchange among them — gathered the surviving strains and put the yellow potato onion back into circulation. The bulbs you plant descend directly from that rescue.