Growing onions without starting from seeds offers significant advantages in speed and reliability for home gardeners. These methods rely on the plant’s natural ability to regenerate from existing structures, such as small bulbs or root plates, bypassing the slow germination phase. Using a non-seed method, like a pre-sprouted bulb or a kitchen scrap, provides a quicker path to harvest and simplifies the cultivation of both full-sized bulbs and continuous green onion harvests.
Growing Onions from Sets
Onion sets are miniature, immature bulbs grown from seed the previous year and dried for storage. This is the most reliable non-seed method for producing mature, full-sized bulbs in a single season. The small bulbs are past the fragile seedling stage and possess stored energy for vigorous initial growth. Choose sets smaller than three-quarters of an inch in diameter, as larger bulbs are more likely to “bolt,” or prematurely send up a flower stalk, halting bulb development.
Planting should occur in early spring when the soil is workable, maximizing the growing season before bulbing is triggered. Onions thrive in loose, well-draining soil with a pH between 6.0 and 7.0. Gently press the sets into the soil so the pointed tip is just visible above the surface. Avoid burying them deeper than two inches, as deep planting restricts the outward swelling of the bulb.
Spacing determines the final size of the mature onions. Space sets four to six inches apart for large storage bulbs. If harvesting some as thinner green onions, plant them closer, around two inches apart, and thin them out later. Apply a light complete fertilizer (e.g., 10-10-10) immediately after planting to encourage strong root development and ensure consistent moisture during the initial rooting phase.
Regrowing Scallions and Green Onions
Regrowing scallions provides a fast and continuous harvest, often yielding new growth within days. This process utilizes the white root end of a store-bought scallion, which contains the basal plate where new leaves emerge. The technique involves cutting the green stalks one to two inches above the root section, leaving the white bulb and roots intact.
The simplest method is the water glass technique, placing the root ends in a shallow glass of water on a sunny windowsill. New shoots often appear within 24 to 48 hours, growing rapidly. While water allows for immediate regrowth, the plant’s vigor and flavor diminish without external nutrients. For a longer-lasting, healthier supply, transfer the rooted cuttings into a small pot filled with moist potting soil.
When planting in soil, bury the root end so the white bulb is covered, with the cut top just above the soil line. This provides access to nutrients, resulting in thicker, more flavorful regrowth. Continuous harvesting is achieved by snipping the green leaves about an inch above the soil surface, prompting regeneration.
Propagating New Onions from Kitchen Scraps
Mature storage onions (yellow or red varieties) can generate new plants from their root plate. This method involves saving the bottom one to two inches of the bulb, ensuring the root end is fully intact. This section provides the necessary energy reserves to initiate new growth.
Before planting, leave the cut piece exposed in a dry area until the surface forms a callous. This drying process prevents the tissue from rotting once placed in the soil. Plant the calloused root section in a container or garden bed, covered with a thin layer of soil, ensuring the roots face down.
The original bulb material will decompose, but the basal plate will sprout new shoots, often producing multiple stems. Each emerging shoot can develop into a separate, smaller onion bulb. To encourage bulb formation, separate and replant the emerging shoots a few inches apart once they are robust.
Ongoing Care and Harvesting Non-Seed Onions
Once established, all non-seed onions require full sun, ideally 8 to 10 hours of direct light daily, especially as bulbs begin to form. Because onions have shallow root systems, they are sensitive to drought and require consistent moisture, typically about one inch of water per week.
During the main growing season, onions benefit from regular applications of a high-nitrogen fertilizer every two to three weeks, which promotes the foliage growth that fuels bulb expansion. Stop both fertilizing and watering once the bulbs begin to swell and the leaves start to soften, about a month before the expected harvest. This cessation helps the bulb mature and cure properly for storage.
For mature bulb onions, readiness is indicated when the green tops begin to yellow and fall over naturally. Once about half of the tops have collapsed, the neck can be bent over to speed up the final drying process. Gently lift the bulbs from the soil a week later. Green onions can be harvested continuously once the leaves are six to eight inches tall by simply snipping the tops as needed.