Perennial onions make a beautiful addition to any vegetable garden. Not only are they easy to prepare, but once they get going you can harvest them at any size, at any time of year.
While most onions are known as annual vegetables, grown from bulb sets in spring or late fall, nearly all types of onion are in fact, perennial alliums. The difference here is the hardiness of these persistent bulbs, which will come back year after year, even through temperatures as low as -40°F.
What are perennial onions?
The most important thing to understand about perennial onions is that the title covers every species, cultivar, and type of onion there is. Onions are bulbous biennial plants, which, after their first year will spread by seed, bulblets, and by bulbs, just like any other layered bulb.
In their first growing year, onions produce small bulbs, packed full of energy, with the sole purpose of producing stunning flowers in their second year. After that, they will continue to flower in the garden like any other allium.
What are ‘hardy’ perennial onions?
The only difference between perennial onions and ‘hardy’ perennial onions is their tolerance to cold conditions. Hardy plants are defined by locations, rather than species, but as a general rule, they will survive prolonged frosts and temperatures below -20°F.
The alternative is growing tender onions (those that won’t survive cold temperatures) or treating your crop as an annual by harvesting every bulb and cutting off flower heads.
There are advantages and disadvantages of growing hardy perennial onions over those treated as annuals too:
How to grow perennial onions
Onion seeds are stunning up close, with a texture like cracked flint, and a deep black outer skin, but not all onions grow that way. Most of the onions usually referred to as perennial onions, or hardy perennial onions, actually develop bulblets instead of seeds.
The incredible adaptation means that, rather than setting seed, the flower spike, or scape, produces miniature bulbs, that instantly begin to sprout in fall when the stem droops into contact with soil. These tree onions, or walking onions, are becoming much more popular, particularly in no dig gardens, or as part of a permaculture growing plan.
The five different groups of hardy perennial onions to grow are listed below, with some simple details on hardiness, and growing methods. Later I’ll share some of my own favorite cultivars from within each family.
How to grow each type of perennial onion (by group):
|Walking Onions / Tree Onions / Egyptian Onions||Hardy to -40°F||Leave to flower, let bulblets droop and sprout in fall.|
|Spring Onions & Welsh Onions||Hardy to -20°F||Leave bulbs to multiply. Either remove flowers for bigger, milder bulbs or leave flowers and save seeds.|
|Chives||Hardy to -40°F||Leave to flower for self-seeding and divide clumps after the last spring frost.|
|Potato Onions||Hardy to -30°F||Leave bulbs to multiply in the ground. Remove spent flowers to discourage seeding.|
|Ramps||Hardy to -40°F||Divide clumps, or leave to self-seed. Will spread slowly.|
The 10 best perennial onion varieties to grow (and how)
1. Wild Onion/Meadow Garlic (Allium canadense)
Wild onions are a perennial weed native to Texas but can be controlled in garden settings. Their flowers, stems, and bulbs are edible.
2. Geyer’s Onions (Allium geyeri)
The mild flavor of Geyer’s onion makes its leaves and bulbs ideal for stews, casseroles, and soups, and its flowers can be used as a garnish for savory dishes too.
3. Ramp Onions (Allium tricoccum)
Ramps are a gorgeous wildflower to grow at home. They do spread but can be controlled with container planting or raised beds, and the whole bulb is edible, with wide leaves that wilt down into sauces like leek-flavored spinach.
4. Nodding Onion (Allium cernuum)
Nodding onion is used similarly to chives or spring onions, with small edible bulbs and mildly flavored stems.
5. Prairie Onion (Allium stellatum)
Prairie onions are perfect for permaculture planting, as they self-seed, and spread easily from bulbs, with gorgeous flowers topping off entirely edible plants with a reasonably strong onion flavor in all parts.
6. Small Yellow Onions (Allium flavum)
The leaves flowers and stems of this stunningly vivid yellow flower are all edible, but the real flavor is in the bulb. The small onion bulb can be used just like regular onions but doesn’t store very well.
7. Potato Onions (Allium cepa var. Aggregatum ‘Potato onion’)
Potato onions are the perfect example of a hardy onion, with a bold flavor and a traditional shape. As the bulbs develop, year after year, they form clumps from one root plate, eventually dividing themselves into a dense clump of edible bulbs.
8. French Red Shallots (Allium oschaninii)
French Red Shallots are one of the most valuable shallot varieties you can buy, and super easy to grow at home. They taste good, they look good and they store well. What’s not to love?
9. Egyptian Walking Onions (Allium proliferum)
Also called tree onions, walking onions, and topsetting onions for their impressive ability to create new bulbs at the top of stems. They need a lot of space to grow well but are an exciting addition to any vegetable garden.
10. Blue Globe Onions (Allium caeruleum)
The flowers of blue globe onions are beyond beautiful, so you’d be forgiven for grouping them in with the inedible alliums, but every part of this magical garden plant is edible.
Hardy perennial onions are worth growing if you’re short of time, or want to experiment with more sustainable gardening practices. They’re perfect for no dig gardens, and fit in beautifully to wild gardens too, with little to no need for fertilizers, soil amendment, or water.
As mostly native species, hardy onions are great for wildlife too, with a much wider range of flavors than the traditional yellow or white onions we grow mostly as annual crops. Whatever you do, don’t let the idea of growing something new intimidate you. Some hardy perennial onions are well-known varieties, and others less so, but all are worth a try.