Growing onions from store-bought items offers an accessible entry point into home gardening. This method leverages the regenerative capacity of the Allium genus, turning kitchen scraps into fresh produce. Onions can reactivate dormant growth points, allowing gardeners to utilize the root ends of greens or the entire bulb to initiate new growth cycles. This provides a sustainable way to maintain a continuous, small-scale harvest.
Regrowing Scallions and Green Onions
Regrowing the green tops from scallions is the quickest method for a continuous harvest. Cut the green stalks about one inch above the white root base, leaving the attached roots intact. Place this root end, with the roots submerged, into a small glass of water. Ensure the cut surface remains above the water line to prevent rot. New green shoots will emerge within a few days from the central growing point.
Alternatively, planting the root end directly into potting mix provides a more nutrient-rich environment for sustained production. Bury the white root base in the soil, leaving only the top quarter inch exposed, and keep the soil consistently moist. The soil method encourages a stronger plant structure and reduces the need for frequent water changes compared to the water glass method.
This technique relies on the plant’s stored energy reserves to quickly produce new leaf blades. Since the plant is focused on foliage production, it will not develop into a large, mature storage onion bulb. Instead, it offers a continuous supply of greens that can be snipped off repeatedly as they reach a usable height, often regenerating within a week.
Planting Sprouting Bulbs for New Onions
Producing a new storage onion bulb requires starting with a mature onion that has begun to sprout internally, identifiable by a hard, green shoot emerging from the center top. This sprouting indicates the bulb has broken dormancy. If the sprout is large, the bulb can be planted whole. To potentially yield multiple smaller onions, the bulb can be carefully sliced into two or four sections. Ensure each section retains a portion of the basal plate, the hard, flat area at the bottom where the roots emerge.
Each section containing a basal plate should be planted individually in prepared garden soil or a container. Place the section with the sprout facing upward, covering the bulb just beneath the soil surface, about one to two inches deep. Planting the sprouted bulb mimics the natural lifecycle, using stored energy to establish roots and foliage before initiating a new bulbing process.
Proper spacing is necessary to allow for the expansion of the new bulbs. Plant them at least four to six inches apart to prevent overcrowding, which can restrict subterranean development and lead to smaller bulbs that do not store well. This process takes several months, as the plant must first develop substantial foliage to photosynthesize the energy required to swell the new bulb tissue.
The developing plant utilizes the energy from the original bulb to grow new roots and leaves, eventually forming one or more new bulbs adjacent to the original structure. New bulb formation is triggered by photoperiod (day length) and is a much slower, more resource-intensive process than simply regrowing the tops.
Ensuring Proper Growing Conditions
Onions require a minimum of six to eight hours of direct sunlight daily for optimal growth, whether the goal is continuous greens or a new bulb. They are cool-season crops, thriving in temperatures between 55°F and 75°F. Excessively hot weather can stress the plant and may prematurely trigger flowering, which halts bulb development and changes the onion’s texture.
The planting medium must be well-draining to prevent the delicate root system from succumbing to fungal diseases, particularly Fusarium basal rot. A slightly sandy loam texture is ideal, allowing water to pass through while retaining moderate moisture. Heavy, compacted clay soil should be amended with compost or sand to improve aeration and facilitate unrestricted bulb expansion.
Consistent and regular watering is important, especially during the early stages of foliage growth and bulb swelling. The soil should be kept uniformly moist but never waterlogged. Cycles of extreme drought followed by heavy watering can cause the bulbs to split or crack, compromising the bulb’s structural integrity.
When and How to Harvest
The green tops from scallions can be harvested continuously once they reach about six inches in height. Use sharp shears to snip the outer leaves, leaving the central growing point intact to ensure regeneration. This selective cutting allows the plant to continue producing new foliage for weeks.
Harvesting a new mature bulb requires patience until the plant naturally signals it is ready, typically when the green tops yellow, weaken, and fall over. Once lifted from the soil, the new bulbs should be left to cure in a warm, dry, and well-ventilated area for one to two weeks. This allows the outer skin to dry and seal for long-term storage.