Growing food from kitchen scraps is a simple, sustainable way to reduce waste and keep a fresh supply of produce on hand. Yellow onions are a common staple that can be easily regenerated. The process primarily focuses on regrowing the green, scallion-like tops, which can be harvested multiple times, offering a quick and rewarding experience.
Selecting and Preparing the Onion Base
A successful regrowth project begins with selecting the correct part of the yellow onion: the basal plate. This plate is the firm, slightly woody disc at the bottom of the bulb where the roots and new shoots originate. When cutting the onion for cooking, retain a piece that is at least 1/2 inch to 1 inch thick, ensuring the basal plate remains intact. Keeping this small portion provides the stored energy and nutrients necessary to fuel the initial root and shoot development. Before attempting to grow the scrap, inspect it carefully to confirm the base is firm and shows no signs of rot or mold, which would prevent successful regeneration.
Methods for Initiating Root Growth
Once the onion base is prepared, there are two common methods to stimulate new growth: water or soil. The water method is often the fastest way to see initial results, requiring a glass or jar with just enough water to cover the root end. You can use toothpicks inserted around the circumference of the onion piece to suspend it over a narrow glass, allowing only the base to touch the water. This allows you to visually monitor root development, with new white roots often emerging within a week. The water must be changed every two to three days to prevent the growth of bacteria and mold, which can cause the scrap to deteriorate quickly.
The soil method is ideal for long-term growth. Plant the scrap root-side down in a small container with a well-draining potting mix, covering it with about one inch of soil. Keep the soil uniformly moist but never waterlogged, as excessive moisture can lead to rot. The stored energy in the bulb provides the initial fuel for growth, and new green shoots can be seen emerging from the soil surface within two to three weeks.
Ongoing Care and Long-Term Maintenance
After the initial roots and shoots appear, the ongoing environment plays a large role in the plant’s continued productivity. The onion plant requires sufficient light to photosynthesize and generate energy for new growth, so a sunny windowsill, particularly one facing south or west, is an optimal location indoors. The ideal temperature for growth is room temperature, avoiding extreme cold or excessive heat sources.
If you began the process in water, transplant the base into soil after one to two weeks, or once a substantial network of roots has formed. Continuing to grow in water will lead to thinner, weaker shoots because the water lacks the necessary nutrients that soil provides. When transplanting, use a container with drainage holes and a standard potting mix, burying the base deep enough so the top of the scrap is just covered by the soil.
For soil-based plants, managing moisture is important to prevent the onion from rotting. Allow the top layer of soil to dry slightly between waterings, ensuring the pot drains completely. Over time, usually after several harvests, the original onion base will begin to diminish and eventually exhaust its stored energy. When the new growth becomes noticeably thinner or the base softens, it indicates the plant has reached the end of its productive cycle and should be replaced with a fresh scrap.
Harvesting the New Onion Greens
The primary purpose of regrowing yellow onions from scraps is to harvest the fresh, mild-flavored green tops, which can be used similarly to scallions. This is achieved through the “cut-and-come-again” technique, allowing the plant to regenerate new greens repeatedly. When harvesting, use sharp scissors to snip the green shoots, leaving about one to two inches of growth above the base.
Leaving a small portion ensures the plant can continue to capture sunlight and photosynthesize, which allows it to continue producing new foliage. These regenerated greens offer a milder, more delicate onion flavor than the original bulb and are perfect for garnishing salads, soups, and omelets. While developing a full, new yellow onion bulb is possible, this process is lengthy, taking three to four months, and requires specific environmental conditions and consistent soil nutrients that are difficult to maintain indoors.