Growing onions doesn’t need to be complicated – and it certainly doesn’t require expensive equipment.
One of the simplest and most beginner-friendly ways to start onions is by using something you already have at home: a cardboard egg carton.
This clever method has been used by gardeners for years, and it’s now becoming popular again thanks to how easy, inexpensive, and effective it is.
If you’ve ever struggled with onion seeds drying out, sprouting unevenly, or becoming tangled in big seed trays, this method is a game-changer.
Cardboard egg cartons create the perfect mini-growing chambers for each onion seed or set, keeping them moist, aerated, and organized.
They’re biodegradable, easy to handle, and surprisingly ideal for forming strong, well-rooted onion seedlings.
Why Egg Cartons Are Perfect for Starting Onions
Egg cartons might look flimsy, but their structure is almost tailor-made for sprouting onions. Each cup acts like a mini cell, holding the seed in place, preventing overcrowding, and encouraging downward root growth.
Here’s why they work so well:
They Maintain Moisture
Cardboard absorbs water and slowly releases it back to the soil. This keeps onion seedlings consistently moist – crucial for germination.
They Allow Good Drainage
Unlike plastic containers, cardboard naturally drains excess water so roots never sit soggy.
They’re Biodegradable
You can plant the whole thing directly in the ground when your onions are ready, reducing transplant shock.
They Save Space
Egg cartons fit neatly on windowsills, shelves, or small inside-growing stations.
They Encourage Strong Root Development
The porous material allows oxygen flow, helping roots grow stronger and healthier.
They’re Free
No need for fancy seed trays when one of the best seed-starting containers comes straight from your recycling bin.
In short, egg cartons create ideal growing conditions for onions – especially for beginners who want simplicity.
What You’ll Need to Get Started
You only need a few basic materials:
- A cardboard egg carton (not plastic or styrofoam)
- Potting mix or seed-starting mix
- Onion seeds, onion sets, or sprouting onion bottoms
- Water spray bottle
- A tray to set the carton on
- Plastic wrap or humidity dome (optional)
This method works for all onion types:
- Yellow onions
- Red onions
- White onions
- Sweet onions
- Green onions (scallions)
- Shallots
You can even use it to sprout store-bought onion bottoms before transferring them to the garden.
Step-by-Step Guide: How to Plant Onions in Cardboard Egg Cartons
Step 1: Prepare the Egg Carton
Open the carton and remove the top lid. You’ll only use the bottom portion with the twelve small cups.
Make a small hole in the bottom of each cup if the cardboard has no natural drainage break. Most cartons drain well by themselves.
Place the carton on a plate, tray, or shallow container to catch water.
Step 2: Fill Each Cup With Soil
Fill each carton cup with potting mix, lightly pressing it down so the soil is compact but not tightly packed.
Leave a little space at the top so you can easily cover the seed.
Step 3: Plant the Onion Seeds or Sets
Depending on what type of onions you’re growing, choose the right planting depth:
Onion Seeds: Plant one seed per cup, about ¼ inch deep.
Onion Sets (the small bulbs): Place each set pointy side up in the cup and gently push it halfway into the soil.
Onion Bottoms (cut from store-bought onions): Cut a 1-inch thick bottom from an onion, place it flat side down on the soil, and sprinkle soil lightly around the edges.
Step 4: Water Gently
Use a spray bottle to mist the soil until it is evenly moist. Avoid pouring water directly onto seeds, as this may wash them out or compact the soil too much.
Cardboard naturally absorbs excess moisture and prevents waterlogging – one of its biggest advantages.
Step 5: Provide Warmth and Light
Place the carton in a bright, warm location such as:
- A sunny windowsill
- Under grow lights
- On a kitchen counter where it receives indirect light
Onion seeds germinate best at 65–75°F (18–24°C).
If the air in your home is dry, loosely cover the carton with plastic wrap until seeds sprout. Remove the cover once green shoots appear.
Step 6: Water and Care for Seedlings
Keep the soil lightly moist. Water by misting or by adding water to the tray underneath and letting the carton absorb it.
Rotate the carton every few days to prevent seedlings from leaning toward the light.
Within 10–14 days, your onion seedlings should emerge strong and upright.
When to Move Onions Out of the Egg Carton
Onion seedlings can stay in the carton until they reach 4–6 inches tall. At that point:
- Roots have filled their cup
- The soil may dry faster
- Seedlings need more nutrients
- It’s time to harden them off
The beauty of egg cartons is their easy transplantability.
You can:
Option 1: Plant Each Cup Directly Into the Soil
Cut the cups apart and transplant them individually. The cardboard will decompose naturally.
This prevents transplant shock and allows roots to push through.
Option 2: Remove the Seedlings and Plant Bare-Root
This works well for bunching onions and scallions. Simply tear away the cardboard and plant seedlings directly into prepared garden rows.
Option 3: Transfer to Bigger Pots Before the Garden
If outdoor conditions aren’t ready yet, move each cup to a larger container for continued growth.
This method ensures strong, healthy, well-spaced onion starts – something beginner gardeners often struggle with.
Why This Method Works So Well for Beginners
Onions are forgiving, but they have one downside: very tiny seeds that dry out fast and seedlings that tangle easily. The egg carton solves these issues naturally.
Beginners love this method because:
- It’s clean and organized
- It prevents overcrowding
- Each onion has its own growing cell
- Water retention is perfect for seed starting
- It supports strong, straight sprout development
- It reduces transplant shock drastically
Even kids learning to garden get excellent results using this approach.
Tips to Make Your Onion Carton Garden Even More Successful
Trim Seedlings
If seedlings grow floppy or too tall, trim the tops to 3–4 inches. This encourages stronger bulbs later.
Fertilize Lightly After Sprouting
Use a diluted liquid fertilizer once seedlings reach 2–3 inches.
Avoid Overwatering
The cardboard will break down faster if consistently soaked.
Keep Temperatures Steady
Cold drafts may stunt growth.
Label Your Cartons
If using multiple onion varieties, keep track of which is which.
Yes – and many gardeners actually prefer this method for onion sets.
Because each set is contained, it stays upright, hydrated, and evenly spaced. When you move them into the garden later, the roots are already established.
When to Transplant Onions Outdoors
Onions prefer cool weather and can be planted outdoors even before the last frost in many regions. Once your seedlings are established in their cartons, transplant them when:
- They are at least 4 inches tall
- The soil can be worked
- Nights are consistently above freezing (for most varieties)
Plant onions 4–6 inches apart with rows spaced 12–18 inches apart.
Planting onions in cardboard egg cartons is one of the smartest, simplest, and most cost-effective methods for starting onions at home.
