Green onions (scallions or spring onions) are a common source of confusion for gardeners regarding their life cycle. Whether they are perennial depends entirely on the specific plant species being grown. Many green onions found in grocery stores are immature versions of the common bulbing onion, Allium cepa, which is typically an annual or biennial plant. However, a distinct species exists that is a true perennial, capable of returning year after year, separating a one-time harvest from a continuously producing patch.
Identifying Perennial Varieties
The true perennial green onion belongs to the species Allium fistulosum, commonly referred to as the Welsh Onion, Bunching Onion, or Japanese Bunching Onion. This species is non-bulbing; it does not form the large storage bulb characteristic of its annual relatives. Instead, it features an elongated white base and hollow green foliage that grows in dense, slowly spreading clumps. These perennial varieties multiply through tillering, where new shoots continuously emerge from the base, creating an expanding cluster. Look for varieties explicitly labeled as “bunching” or “evergreen,” such as ‘Evergreen Hardy White’ or ‘White Lisbon’.
Cultivating Green Onions for Longevity
Harvesting and Division
Maintaining perennial green onions requires a specific harvesting technique that leaves the regenerative parts intact. To ensure regrowth, cut the greens one to two inches above the soil line, leaving the white base and root system undisturbed. This allows the remaining tissue to photosynthesize and draw energy into the underground structures for rapid new shoot development. Over time, a single plant will thicken into a dense clump, requiring division to maintain vigor and productivity. Gardeners should separate these crowded clumps every one to two years, ideally in early spring, and replant the individual divisions a short distance apart.
Cold Tolerance
Perennial bunching onions demonstrate significant cold tolerance, capable of surviving harsh winters, often down to USDA Hardiness Zone 3. In colder climates, the foliage may die back or go dormant after the first hard frost, but the underground root system remains alive. Applying a thick layer of mulch, such as straw or shredded leaves, over the dormant patch in late fall provides insulation, protecting the roots and stimulating earlier growth the following spring.
Life Cycle Differences in Onion Types
The fundamental difference between perennial and annual green onions lies in their genetic programming for reproduction and storage. Allium fistulosum is naturally a non-bulbing species, oriented toward continuous vegetative growth and clonal reproduction through the constant production of offsets, forming the characteristic clump. This perpetual clumping structure allows the plant to be repeatedly harvested without dying. In contrast, scallions derived from the common bulb onion, Allium cepa, are harvested before the plant completes its biennial life cycle. The A. cepa plant is focused on accumulating energy into a single, large storage organ (the bulb) to survive a dormant period and flower in its second year. When an immature A. cepa is pulled for its green stalks, the entire life-sustaining structure is removed, making it an annual harvest. Even if the base is replanted, the subsequent growth is temporary, as limited resources are quickly exhausted.