Whether an onion plant returns to the garden each year depends entirely on the specific Allium variety. Most onions grown for large, storable bulbs, such as common yellow or red globe types, are not designed to survive and regrow over multiple seasons. However, the diverse Allium family contains many members that are true perennials, offering a continuous harvest of greens or small bulbs year after year. Understanding the natural life cycle of each type clarifies why some onions “come back” and others do not.
The Standard Bulb Onion Life Cycle
The large, globe-shaped onions grown for cooking and storage are typically treated as annuals, meaning they are planted and harvested within a single growing season. Botanically, these onions are biennials, meaning their complete life cycle naturally spans two years. In the first year, the plant grows leaves, which gather energy to form the large, fleshy underground bulb. This bulb is a food storage unit the plant uses to survive a dormant period.
Gardeners intentionally interrupt this two-year cycle by harvesting the bulb at the end of the first growing season, once the foliage begins to dry and fall over. Once this primary bulb is removed from the soil, the individual plant is finished and will not regenerate the following spring. The goal of cultivating this type is the single, large, concentrated bulb, not continuous perennial growth.
Allium Varieties That Return Annually
While the common storage onion is harvested after one year, many other members of the Allium genus are true perennials and return season after season. These varieties have a different growth habit, focusing on clump formation and division rather than a single massive bulb.
- Chives (Allium schoenoprasum) form dense clumps that can be harvested for their mild, hollow green leaves from early spring onward.
- Multiplier onions (potato onions) return by dividing underground; a single planted bulb splits into a cluster of smaller bulbs that can be separated and replanted.
- Welsh onions (Allium fistulosum), or perennial scallions, spread through small offsets and provide a continuous supply of green tops without forming a prominent bulb.
- The unique Egyptian Walking Onion (Allium x proliferum) propagates itself by forming small bulbils at the top of its flowering stalk, which fall over to “walk” the plant to a new location.
When a Leftover Bulb Sprouts
Confusion often arises when a common bulb onion is accidentally or intentionally left in the ground past the first harvest. If a bulb survives a mild winter, it uses its stored energy the following spring to complete its biennial life cycle. This second-year growth involves “bolting,” where the plant rapidly sends up a thick, central flower stalk.
The plant’s energy is entirely redirected to producing flowers and seeds, a reproductive effort that depletes the bulb’s reserves. The resulting bulb from this second-year growth is often woody, tough, and may have split into several smaller, low-quality sections. While the original bulb has indeed “come back,” it has done so to reproduce, not to provide another edible, storable bulb, marking the end of that specific plant’s life.