You can grow an onion from an onion, a popular experiment for home gardeners looking to reduce kitchen waste. Onions possess the biological mechanisms necessary to regenerate, allowing a new plant to emerge from a discarded portion of the original bulb. This process leverages the plant’s natural ability to produce new roots and foliage from its basal plate (the hardened tissue at the bottom of the bulb). While this method is straightforward and highly accessible, understanding the specific techniques used for different onion scraps helps manage the resulting harvest.
Starting a New Plant from the Base of an Onion
One of the most common methods involves planting the root end, or basal plate, of a standard bulb onion that would otherwise be composted. To start this process, you should slice off the bottom section of the onion, ensuring you keep approximately one to one-and-a-half inches of the bulb tissue attached to the root plate. This remaining tissue provides the initial energy reserves for the new plant to establish itself.
The cut base can be allowed to dry slightly for a few hours to form a protective callous, then placed root-side down in a small container of water until new white roots begin to emerge. Alternatively, you can plant the section directly into a pot filled with well-draining soil, covering it with about an inch of dirt. Successful growth requires a location that receives at least six hours of direct sunlight daily and soil that is kept consistently moist but never waterlogged.
Once planted, the existing root structure will anchor the piece, and new green shoots will soon push up through the soil surface. If the initial piece of onion was large enough, it may contain multiple growth points, and gardeners can later separate the newly established plants to give each one adequate space to develop. This technique mimics planting a small, immature bulb.
Utilizing an Onion That Has Already Sprouted
A different approach uses a whole onion bulb that has already begun to sprout with long green shoots. Sprouting indicates the onion is breaking dormancy and beginning its reproductive phase. Instead of planting the entire bulb, which can lead to rotting or crowding, the best practice is often to dissect the sprouted onion gently.
Peel away the layers of the old onion bulb to reveal individual growth points, or sprouts, each with a tiny root base. By separating these sprouts, you can effectively turn one sprouted onion into two or three distinct new plants. Each separated sprout should then be planted individually in soil, positioned just deep enough so the root base is covered and the green tip is above the surface. This separation prevents competition and allows each emerging plant to focus its energy on establishing its own root system and foliage.
Expectations: Growing Scallions Versus New Bulbs
The primary difference between growing onions from scraps and growing them from seeds or sets (small, dormant bulbs) lies in the final harvest. When you plant a scrap or a sprouted bulb, the plant’s immediate goal is to produce leaves, which are the green tops commonly known as scallions or green onions. These greens can be harvested continually by clipping them an inch or two above the base, allowing the plant to regrow new foliage repeatedly.
While the plant is growing greens, the energy stored in the original bulb scrap is gradually depleted. This method often results in the formation of multiple smaller, sometimes misshapen, bulblets or offsets rather than a single, large storage onion like the one you originally purchased. The plant is focused on division and leaf production, not the substantial storage bulb formation required for a lengthy shelf life.
For a harvest of large, storable onions, the standard method is to plant from seeds or onion sets. These methods ensure the plant has a full growing season to mature and concentrate its energy into developing a single, robust storage bulb. Regrowing from scraps produces a continuous supply of fresh onion greens for cooking, not mature bulbs for storage.