I’ve always been fascinated by how much food you can actually regrow from kitchen scraps. Onions are one of those vegetables that seem to keep on giving, and for years I’d toss the root ends without a second thought. Then I started experimenting, and what I found was pretty interesting: you can absolutely grow new onions from an old one, and it’s a lot simpler than I thought.
It’s not quite as straightforward as just sticking it in the ground and hoping for the best. I made that mistake for years, wondering why I’d get a lot of green tops but no actual bulbs. There are a few tricks to it, especially if you’re aiming for a harvestable onion and not just green shoots.
The Simplest Start: Planting the Root End
This is where most people begin, and it’s a great way to get green onions quickly. I’ve done this countless times on my kitchen windowsill. When you chop an onion, save the bottom inch or so, making sure it has the little root plate attached.
- Find the Root Plate: Look for the flat, slightly discolored bottom where the roots emerge.
- Trim Carefully: Cut about 1 inch from the base, leaving some of the white onion flesh attached.
- Water First (Optional but Recommended): I usually suspend the root end in a shallow dish of water, just enough to cover the bottom, for a few days. This gets the roots actively growing before it goes into soil. You’ll see green shoots appear surprisingly fast.
- Into the Soil: Once you have a decent root system (even a few short roots are enough), plant it in a pot with good drainage, burying the root plate and just a little bit of the white onion flesh. Keep the soil consistently moist.
What you’ll get from this method are primarily green onions or scallions. The original piece of onion will sprout new green tops. You can snip these as needed, and they’ll often regrow several times. If you leave them long enough, sometimes a small new bulb will form, but it won’t be a large, storage-quality onion like the one you started with.
Growing Whole Onions from a Sprouted Bulb
Sometimes, you find an onion in your pantry that’s already started to sprout. Don’t toss it! This is a perfect candidate for growing new bulbs.
- Inspect the Sprout: Look at the green shoots emerging from the top. Often, a single onion will have multiple sprouts inside.
- Cut it Lengthwise: Instead of planting the whole sprouted onion, I’ve had much better luck cutting it in half or even quarters, making sure each section has a sprout and some of the root plate attached.
- Separate the Sprouts: If you gently peel back the layers, you might find individual small onion bulbs forming around the base of each sprout. Carefully separate these, ensuring each has its own root system.
- Planting: Plant these individual sprouts or sections directly into the soil, about 1 inch deep. Space them 4-6 inches apart if you’re planting multiple in a larger container or garden bed.
With this method, you’re essentially giving each sprout a chance to develop into its own onion. I’ve found that these often produce small to medium-sized bulbs that are great for cooking, though they might not be as uniform as those grown from sets or seeds.
The Multiplier Effect: Perennial Onions and Division
There are certain types of onions that are absolute workhorses in the garden, and these are the ones I really love. Varieties like Egyptian Walking Onions (also called tree onions) or potato onions are perennials. You plant them once, and they just keep on giving.
- Egyptian Walking Onions: These are fascinating. They grow small bulbs on top of their stalks, which then get heavy, bend over, and ‘walk’ to a new spot to root. I’ve got a patch that’s been going for years with minimal intervention. You just pick the bulbs off the top or dig up the ones at the base as you need them.
- Potato Onions (Multiplier Onions): You plant one bulb, and it divides into a cluster of several new bulbs underground. In the fall, I dig up the cluster, separate the individual onions, and then replant a few for the next season. It’s a self-sustaining cycle. I rarely buy shallots or small onions from the store anymore because of these.
If you’re planting these multiplier types, give them a bit more space – around 6-8 inches between individual bulbs – to allow for that division. They’re also quite hardy and can often overwinter in the ground, even in colder climates.
Planting and Care for Onion Scraps
Whether you’re planting a root end, a separated sprout, or a multiplier onion, the basic care is pretty similar.
Soil and Location
Onions need well-draining soil. I always amend my garden beds with plenty of compost, which helps with drainage and provides nutrients. They’re also sun-lovers, needing at least 6-8 hours of direct sunlight a day. If you’re growing in pots, make sure the pot is at least 6 inches deep and has good drainage holes.
Watering
Keep the soil consistently moist, especially when the plants are young and actively growing. Onions have shallow root systems, so they dry out quickly. Once the bulbs start to swell, you can ease up on watering a bit, which helps them cure properly.
Spacing
This is crucial for bulb development. For individual onions, aim for 4-6 inches between plants. If you’re planting in rows, 6-8 inches between rows gives them enough room. Too close, and you’ll end up with a lot of small, undeveloped bulbs.
When to Harvest
For green onions, you can start snipping the tops once they’re about 6 inches tall. For bulb onions, whether from sprouts or multipliers, they’re ready when the leaves start to turn yellow and fall over, usually in late summer or early fall.
- The ‘Neck’ Test: Once the tops fall, the neck of the onion (where the leaves meet the bulb) will start to soften. This is a good sign they’re ready.
- Curing: After pulling them from the ground, I leave them on the soil surface for a few days to dry in the sun, or in a warm, dry, protected spot if rain is expected. This ‘curing’ process helps them store longer. Then, I brush off any loose dirt and store them in a cool, dark, well-ventilated area.
My Takeaway
Growing onions from existing ones is a great way to reduce waste and get a continuous supply of green onions, and with multiplier varieties, even full-sized bulbs. It’s a bit of a different process than planting from seed or sets, but once you get the hang of it, it’s incredibly rewarding. I’ve found that paying attention to spacing and soil drainage makes all the difference in getting a good harvest. Start small, experiment with a few methods, and you’ll likely find yourself with a steady supply of fresh onions from your own garden.
