I stared at my grocery receipt last Tuesday and realized I’d spent six dollars on three basic yellow onions. It wasn’t the first time I’d felt ripped off in the produce aisle, but it was definitely the last.
Turns out the fix was sitting right there in my kitchen recycling bin. One empty egg carton and a few leftover kitchen scraps completely ended my onion-buying days.
Here’s exactly how we grow endless onions in our own apartments, no expensive seed-starting kits required.
Why You Should Plant Onions in Egg Cartons
Don’t throw those cardboard cartons away. They’re basically free, perfectly sized rooting nurseries. When you’re trying to regrow vegetables from kitchen scraps, the biggest enemy is rot. If the soil stays too wet, the roots turn to mush before they can sprout.
Cardboard naturally breathes and wicks excess moisture away from the soil. This means your onion roots won’t sit in a stagnant puddle and rot (trust me, I learned the hard way using plastic yogurt cups). A foolproof system.
Honestly, those expensive plastic seed-starting trays are a total waste of money. The cheap cardboard carton works better, and it’s already in your house.
Everything You Need to Get Started
You only need three things for this project. Keep it simple.
- A cardboard egg carton: It must be cardboard. Plastic or styrofoam won’t breathe and will suffocate your roots.
- Standard potting mix: Don’t use heavy garden topsoil. You need something light and fluffy.
- Onion scraps: The hairy bottom end you usually throw in the compost bin. You need about half an inch of the actual onion bulb still attached to the roots.
Before you start planting, you need to prepare the carton. It’s a quick process, but don’t skip the drainage step.
Setting Up Your Onion Nursery
Start by cutting the lid off the carton. You won’t need it. Take a pen or a skewer and poke a tiny hole in the bottom of each egg cup. Drainage is critical here.
Fill each little cup about halfway with your potting soil. Don’t pack it down tight. The roots need loose soil to push through as they grow. If the soil is compacted, they’ll struggle to establish themselves.
Now, take your onion scrap. Look at the bottom where the dried, wiry roots are. That side goes down. Press it gently into the potting soil until the roots are covered, leaving the flat cut top exposed to the air.
Water it lightly. You want the soil damp, not soaking wet. I usually just use a small spray bottle to mist the surface for the first few days, so I don’t accidentally drown them.
Once you’ve got the soil right, the rest is mostly patience.
Where to Put Your Egg Carton
Onions need light to start pushing up those new green shoots. Place your egg carton on the sunniest windowsill you have. A south-facing window is ideal, but east or west will work too.
Since cardboard is porous, it’s going to leak water when you water your onions. You absolutely need to place the carton on a waterproof tray or a baking sheet, unless you want to ruin your windowsill.
Check the soil every two or three days. When the top feels dry to the touch, give it a light watering. The cardboard will also start to feel dry and slightly stiff when it needs water.
The Waiting Game and The Sprout
John tried this with a red onion scrap that was looking incredibly rough. For the first four days, nothing happened. We just stared at a piece of old onion sitting in dirt. Then, on day five, a tiny, bright green shoot pushed up from the center. Two weeks later, he had an eight-inch scallion ready to chop for tacos.
That’s the beauty of this method. It’s fast.
You can expect to see new green growth within a week. These green shoots are entirely edible. You can snip them off with scissors and use them exactly like scallions or green onions. The best part? The onion will just keep pushing up new shoots. You can harvest the greens three or four times from a single scrap before the plant finally exhausts itself.
If you’re interested in other ways to maximize your small space, you should check out our guide on 20 vegetables to grow from kitchen scraps. It pairs perfectly with this project.
Moving Them Outside
If you don’t just want green shoots and you actually want to grow a full, round onion bulb, you’ll need to transplant them.
The egg carton is a nursery, not a permanent home. Once the green shoots are about four inches tall and the roots have started to fill the little cardboard cup, it’s time to move them.
You can transplant them into a larger container on your patio or directly into a garden bed. Here’s the trick with cardboard egg cartons: you don’t even need to take the plant out of the cup. Just tear the individual cup away from the rest of the carton and plant the whole thing in the ground.
The wet cardboard will break down entirely in the soil within a few weeks, and the roots will push right through it. It completely eliminates transplant shock because you never disturb the roots. Zero stress for the plants.
Make sure your new container or garden bed gets at least six hours of direct sunlight a day. Onions are heavy feeders, so mix in some compost when you plant them. If you’re short on space and growing on a balcony, you might also like these 15 budget-friendly DIY raised garden beds made from easy-to-find materials.
Troubleshooting Common Issues
Sometimes things don’t go perfectly. If your onion scrap turns mushy and smells bad, you watered it too much. Throw it away and start over with a fresh scrap, using half as much water next time.
If the green shoots are pale yellow and falling over, they aren’t getting enough light. Move them closer to the window or supplement with a small desk lamp.
If you see tiny gnats flying around the soil, it’s a sign the potting mix is staying too wet. Let the top layer of soil dry out completely between waterings.
Frequently Asked Questions
Can I do this with garlic or shallots?
Yes. Garlic cloves and shallot bottoms root exactly the same way in an egg carton. Garlic will give you delicious garlic scapes (green shoots) in a few weeks.
Do I need to buy special seed-starting soil?
No, standard potting mix works perfectly fine. Don’t waste your money on the premium seed-starting bags for this. The onion scrap already has all the energy it needs stored in its bulb to push out the first flush of roots and leaves.
How long does it take to grow a full onion bulb?
If you transplant your sprouted scrap into a larger pot or garden bed, it will take about 90 to 120 days to form a mature, harvestable bulb, depending on the variety and your climate.
Why is my egg carton getting moldy?
A little white fuzz on the outside of the cardboard is normal and harmless. It just means the cardboard is damp. If it bothers you, you can wipe it off with a paper towel, but it won’t hurt the onions.
Stop Overpaying for Produce
Growing your own onions from scraps is one of those really satisfying garden projects that actually saves you money. Give it a try this weekend. You’ll wonder why you didn’t start saving your onion bottoms sooner.