Winter onions are cold-hardy, perennial members of the Allium genus, including varieties like Welsh onions (A. fistulosum) or walking onions (A. x proliferum). They are valued primarily for providing fresh, mild onion greens much earlier than standard bulb onions. Understanding the proper timing is necessary for maximizing the yield, whether harvesting greens, underground bulbs, or propagating the plant.
Timing for Continuous Green Harvest
The primary benefit of cultivating winter onions is the early and continuous availability of their scallion-like leaves. Harvest can commence as soon as the foliage reaches a usable size, typically about the diameter of a pencil, which occurs in early spring following the first flush of growth. Starting the harvest early encourages the plant to allocate energy toward producing new shoots throughout the season.
To ensure the plant’s regeneration and ongoing production, selectively remove only the outer leaves from the cluster. Make a clean, sharp cut about one inch above the basal plate, leaving the central, younger shoots intact to support the root system. Removing too many leaves or cutting too close to the base will deplete the plant’s carbohydrate reserves and slow its ability to recover for subsequent harvests.
Continuous harvesting can be sustained throughout spring and summer, slowing down only during periods of extreme heat or drought. Allow the plant a recovery period of three to four weeks between harvests for the foliage to regrow sufficiently. This regular trimming helps prevent the plant clump from becoming overly dense, which can reduce overall vigor and the quality of the green shoots.
The goal is to maintain a balance between consumption and plant health, ensuring enough green material remains to fuel regrowth. Regular trimming also helps delay or prevent the plant from initiating the flowering process. Once the scape, or flower stalk, begins to form, the leaves often become tougher and less palatable as the plant diverts energy toward reproduction.
Harvesting the Underground Bulbs
Harvesting the entire underground cluster of bulbs is typically done to thin an overgrown patch or to utilize the small, mild onion bulbs. Unlike standard bulb onions, winter onion bulbs are generally ready when the foliage begins to naturally senesce. This maturation process is signaled by the leaves starting to yellow and flop over, often occurring in late summer or early fall, depending on the variety and climate.
The bulbs are ready for extraction when approximately two-thirds of the foliage has died back and dried, indicating the plant has stored maximum energy in the subterranean structure. At this stage, the neck of the plant has softened, making it easier to separate the bulb from the stalk. Carefully lift the entire clump from the soil using a garden fork, working outside the base to minimize damage to the root system and the tight cluster of bulbs.
Once lifted, gently brush away the soil, and separate the individual bulblets from the main cluster by hand. These bulbs are smaller than traditional onions but offer a milder, sweeter flavor profile. If replanting, select the largest, most vigorous bulbs for immediate reinsertion into the soil; the remaining ones can be used or prepared for storage.
Collecting and Planting Aerial Bulbils
A unique characteristic of the walking onion (Allium x proliferum) is its reproduction through small, self-propagating aerial sets, or bulbils, which form at the top of the flower stalk. These bulbils replace the typical flower head and are the plant’s primary mechanism for “walking” or relocating across the garden. The optimal time for collection is when the bulbils are fully mature, dry, and have begun to weigh down the stalk toward the ground, usually occurring from mid-to-late summer.
When ready, the bulbils will have developed a papery, dry skin and detach easily from the stalk, indicating they are dormant and ready for planting. Harvesting them at this stage ensures they possess the highest concentration of stored energy necessary for successful germination and growth. The purpose of collecting these sets is purely for propagation, as they are too small and intensely flavored for practical culinary use.
Plant the collected bulbils immediately after harvest to ensure the highest rate of establishment. Separate and plant them individually about one inch deep, spacing them approximately six inches apart in well-drained soil. Alternatively, they can be stored briefly in a cool, dry place and planted in the fall, allowing them to establish roots before winter dormancy. Planting the bulbils starts new, vigorous plants that will produce greens the following spring and eventually develop underground bulbs.
Curing and Storing Winter Onions
Post-harvest handling varies based on the plant part harvested. Fresh greens, which are primarily water, should be treated like scallions and stored short-term in the refrigerator. They can be placed upright in a container with a small amount of water or wrapped loosely in a damp paper towel and kept in the crisper drawer for up to a week.
If underground bulbs were harvested in late summer or fall, they require curing to prepare them for long-term storage and prevent decay. Curing involves drying the bulbs and their attached foliage in a warm, low-humidity location with good air circulation. This process typically takes one to three weeks, depending on the ambient temperature and humidity.
Curing allows the outer layers of the bulb to dry and tighten, effectively sealing the bulb and concentrating the flavor. Once fully cured, trim the dried foliage. The bulbs should then be stored in a cool, dark environment, ideally between 32 and 40 degrees Fahrenheit, allowing them to remain viable throughout the winter.