A potato onion is a type of multiplying onion that reproduces by dividing into a cluster of bulbs underground, similar to the way garlic grows. It belongs to the same species as common onions (Allium cepa) but sits in the Aggregatum Group alongside shallots. Despite the name, it has no relation to potatoes. The name likely comes from the way the bulbs multiply underground in a nest, resembling the way potatoes form.
How Potato Onions Differ From Regular Onions
Standard onions grow from seed, producing a single bulb per plant. Potato onions reproduce primarily by division: you plant one bulb, and it splits into a cluster of new bulbs over the growing season. This makes them functionally closer to garlic in how they propagate, even though they taste like a mild, rich onion.
Potato onions are also closely related to shallots, and the two share the same botanical classification. The key differences are size and shape. Shallots tend to be small and teardrop-shaped, while potato onions are rounder and noticeably larger. In flavor, potato onions lean more toward a standard yellow onion than the sharper, more complex taste of a shallot. Their skin color typically resembles a yellow onion as well, though some red and brown-skinned varieties exist.
A Long History in Home Gardens
Potato onions were once one of the most common onions in European and American home gardens. Research at Linköping University in Sweden found that when Nordic countries began inventorying heritage plants, potato onions turned up in kitchen gardens across the entire region, often with histories stretching back many generations. Families moving to new homesteads would bring their potato onion sets along. In the United States, they were a favored onion among settlers heading west because of their ease of growing and exceptional storage life.
The potato onion may actually be one of the oldest cultivated alliums in Northern Europe. Matti Leino, a researcher at Stockholm University, has suggested that potato onions, not common onions, were likely the alliums cultivated in prehistoric Nordic communities. Alliums appear in some of the oldest written sources from the region, including references on 6th-century gold coins and records of Viking trading journeys. Over 100 distinct potato onion varieties have been collected from kitchen gardens across the Nordic countries, many passed down through families for centuries.
How They Grow and Multiply
The growth cycle is simple. You plant a single bulb in the ground, and over the season it divides into a cluster of new bulbs held together inside the original skin. A large planted bulb typically produces several smaller bulbs, while a small planted bulb often grows into one or two larger bulbs. This inverse relationship is one of the quirks of potato onions and gives growers a natural system: plant the big ones to get lots of small ones, plant the small ones to get a few big ones.
Compared to shallots, potato onions are larger, divide into fewer individual bulbs, and stay enclosed within the parent bulb’s skin longer during the growing process. At harvest, the cluster can be separated by hand. Replanting is as straightforward as pulling one bulb from the nest and putting it back in the ground for next season. Because they rarely need to be started from seed, they’re one of the most low-maintenance alliums a home gardener can grow.
Planting and Growing Conditions
Potato onions prefer fertile, well-drained soil. Plant bulbs about 1 to 3 inches deep, spaced roughly 10 to 12 inches apart, with rows 24 to 36 inches apart. They can be planted in fall or early spring depending on your climate. Fall planting in mild-winter areas gives them a head start, producing larger clusters by summer. In colder regions, spring planting after the last hard frost works well.
They need consistent moisture during the growing season but don’t tolerate waterlogged soil. Once the tops begin to yellow and fall over in mid to late summer, it’s time to cut back on watering and prepare for harvest.
Harvesting and Curing
Harvest when about two-thirds of the green tops have fallen over naturally and the necks (where the leaves meet the bulb) have started to dry and become papery. Research has shown that optimum flavor and sweetness develop when onions reach about 80% foliage die-back. Once your onions hit that stage, don’t wait more than a week or two to pull them, or the bulbs may start to rot or push out new growth.
After harvesting, cure the bulbs in a warm, well-ventilated spot at 75 to 90°F for two to four weeks. This can be done right in the garden if the weather is dry, or in a garage or covered porch if rain is a concern. Leave them until the outer skins and necks are completely dry and papery. Properly cured potato onions store remarkably well, often lasting six months or longer in a cool, dry location. This exceptional keeping quality is one of the main reasons they were so valued by earlier generations of gardeners.
Disease Resistance and Companion Planting
Potato onions have a reputation for hardiness, and research supports their value as companion plants. A study published in Frontiers in Plant Science found that growing potato onions alongside tomatoes reduced the severity of Verticillium wilt, a common fungal disease in tomatoes. When tomatoes were companion-planted with potato onions, disease incidence dropped and symptoms were less severe. Interestingly, the effect came from the interaction between the two plants growing together rather than from the potato onion’s root chemistry alone. Root exudates from potato onions grown in isolation showed no significant antifungal activity.
In northeastern China, where potato onions are widely cultivated, farmers have long used them as companion plants for pest and disease management in mixed cropping systems. Their strong allium scent helps deter certain insect pests, and their general vigor means they rarely need fungicide or pesticide treatment themselves.
Why They Fell Out of Fashion
Despite their advantages, potato onions largely disappeared from commercial agriculture during the 20th century. Modern seed-grown onion varieties offered more uniform sizing, which made them easier to pack and sell. Potato onions, with their variable cluster sizes, didn’t fit neatly into industrial farming. But for home gardeners and small-scale growers, the traits that made them commercially awkward are exactly what makes them practical: they’re self-perpetuating, long-storing, cold-hardy, and rarely need purchased seed after the first year. You simply save a few bulbs from each harvest and replant them.
Interest has been growing steadily among heirloom gardeners and permaculture growers who value plants that sustain themselves year after year with minimal inputs. Several specialty seed companies now carry potato onion sets, and heritage plant networks in Scandinavia, the UK, and North America have been working to preserve the dozens of regional varieties that still survive in private gardens.