Strawberry onion is a perennial vegetable known by several names, including the Tree Onion, Topset Onion, or Egyptian Walking Onion (\(Allium\) \(x\) \(proliferum\)). This variety is distinct from common onions because it does not produce flowers or true seeds. Instead, it develops clusters of miniature bulbs, called bulbils or topsets, at the top of its tall, hollow stalks. These bulbils are small, edible, and serve as the plant’s unique method of propagation. The perennial nature of this onion makes it an easy-to-grow, low-maintenance garden staple, providing harvests year after year.
Establishing the Planting Site
Tree onions perform best when planted in a site that receives full sun exposure throughout the day. While they can tolerate some partial shade, maximum yield and vigor are achieved when they receive at least six to eight hours of direct sunlight daily.
The soil must be well-drained, as excessive moisture can quickly lead to the rot of the underground bulbs. Incorporating organic matter, such as compost or well-rotted manure, improves the soil structure and drainage. The ideal soil pH for these onions is slightly acidic to neutral, typically ranging from 6.0 to 7.0. If the soil is highly acidic, a light application of lime several months before planting can help adjust the pH level.
Planting can successfully occur in either the early spring or the fall, with fall planting allowing the roots to establish before winter dormancy. The bulbils or small base bulbs should be planted shallowly, only about one to two inches deep, with the tip just barely covered with soil. Setting the plants six to eight inches apart allows for good air circulation, or about one square foot per plant if you plan to let the clumps expand significantly.
Routine Maintenance and Seasonal Care
Once established, the perennial onion patch requires minimal ongoing attention to flourish. They benefit from consistent moisture, especially during prolonged dry periods. The soil should be kept consistently moist but never waterlogged, a common cause of failure in all \(Allium\) varieties. Applying a layer of organic mulch around the plants helps to regulate soil temperature, retain moisture, and suppress competing weeds.
These onions are not heavy feeders, and excessive nitrogen can encourage leafy growth at the expense of bulb development. Instead of synthetic fertilizer, an annual application of a one-to-two-inch layer of finished compost in the fall or early spring provides sufficient nutrients. Some growers utilize trench composting around the patch to provide a slow, steady release of organic matter and nutrients.
Pest and disease issues are generally minor, but common onion pests like thrips can occasionally appear during hot, dry summers. Damage from thrips is mostly cosmetic, though severe infestations can reduce plant vigor. In early spring, the application of floating row covers can help prevent onion maggot flies from laying eggs near the base of the plants, protecting the developing root systems.
Harvesting and Culinary Use
The entire strawberry onion plant is edible, offering three distinct harvests throughout the growing season. The most consistent yield comes from the green tops, which can be used like scallions or chives from early spring until the first heavy frost. It is advisable to limit harvesting the greens in the first year to allow the plant to establish a strong root system.
The topsets, the miniature bulbs that form at the top of the stalks, are ready for harvest in late summer, typically between July and September. These bulbils have a mild onion flavor and can be eaten raw, cooked, or pickled like pearl onions. Harvesting the topsets before they become too large will encourage the plant to put more energy into the underground bulb.
The underground bulbs can be harvested in late summer or fall, usually starting in the second year of growth. These base bulbs are more pungent than the topsets or greens and can be substituted for regular onions. When harvesting the underground bulb, the entire plant is removed, so it is necessary to leave some base bulbs in the ground to ensure perennial regrowth.
Managing the Perennial Patch
The unique growth habit of the strawberry onion is what gives it the name “Walking Onion.” As the topsets mature in late summer, their weight causes the tall, rigid stalks to bend over toward the ground. When the bulbils touch the soil, they take root and establish new plants a short distance from the parent clump. This process causes the patch to slowly “walk” or migrate across the garden, potentially spreading up to 18 to 24 inches per year.
Gardeners who wish to control the spread of the patch should harvest the topsets before the stalks flop over. Removing the bulbils redirects the plant’s energy and keeps the patch contained to its original location. Conversely, allowing the stalks to fall naturally is the easiest way to propagate and expand the onion patch into a larger area.
To maintain plant vigor and prevent overcrowding, established clumps of perennial onions should be divided every three to five years. This process is best done in the spring or fall by digging up the entire cluster and gently pulling the bulbs apart. The separated bulbs can then be replanted in a new location, ensuring the continuous productivity of the perennial patch.