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Wondering how to start seeds indoors in an egg carton? I’ve got you covered! This activity is a great way to use those cardboard egg cartons you have laying around. 

This DIY is an easy solution for seed starting when you don’t want to spend money on supplies and/or are trying to simply use what you have! This activity is a great option for kids, and this egg carton seed starter will show them how seeds germinate and how plants begin to grow! If you’re looking for more helps to get kids started gardening, check out my free Kids Gardening Printables!

But these seed trays made from egg cartons can be used by gardeners of all ages, and they’re a great first step if you’ve never started your own seeds before. 

DIY Seed Starters

Skip the peat pots at the hardware store, and plant your flower seeds or vegetable seeds in these small cups. This can be easily done at the kitchen table with a spoon and hardly any dirt contact at all. (Anyone have a dirt-phobe? We’ve got one!)

Another great thing about this activity, is you can use an egg carton instead of throwing it in the trash can. Reuse, reuse! Those egg cartons are also compostable, so find out How to Compost, too! Here’s what you’ll need to make this activity happen:

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Egg Carton Seed Cup Supplies

Here’s what you’ll need to get your seeds growing with just a little soil and just in time for spring planting or fall gardening! 

• 1 paper/cardboard egg carton
• potting mix (we used seed-starting mix)
• flower/plant seeds (zinnias and marigolds are great for this!)
• low container or dish (I used a pyrex dish)
• water spray bottle (optional)

Egg Carton Seed Starters

1. Cut the top off of the egg carton and discard (compost!). Cut down the center, creating two pieces with six cups each. You can choose to leave the “cups” together at this point, or you can cut each cup so they’re separate. That’s the option we chose.
2. Use a sharpie to write on the outside of each cup what will be growing inside. Better yet, let your child or grandchild do this. It’s super easy to copy the flower name from the seed packet right onto the cup, and it’s great writing practice!
3. Begin to fill each egg carton seed cup with soil. you can do this by scooping with the cup itself (dirtier) or with a spoon (cleaner). Putting newspaper down makes clean up a cinch, so I highly recommend this.

4. Place two or three seeds in each cup and lightly cover with soil. This is a great time to talk to your kids about how beautiful and wonderful things can start with just a tiny seed! It’s also a great time to read The Tiny Seed by Eric Carle, even if your kids are a bit older, they’ll still love it, and they can try to mimic Carle’s artwork. 

5. Place cups in a low container and water those babies! I did this at first with a water bottle, so I didn’t wash the seeds away. I also placed some water in the bottom of the dish itself, so the egg cartons would soak it up. This helps to “water” the seeds from the ground up. 
6. Place seed cartons in a sunny spot in the house, and keep them moist, but not soaking wet.

Indoor Seed Starting with Seed Cups

To create a mini greenhouse, you can cover your tray with the egg carton seed cups inside  with saran wrap, or an equivalent wrap. This will help trap in moisture, and create a small greenhouse environment. 

I find this cuts down on how often I need to water. Keeping the container near a warm spot (vent) or in a sunny place will also allow your seeds to germinate more quickly. 

You can also choose to store your seed cups in an old clamshell salad container. This created a perfect greenhouse environment for your growing seeds!

How long until seeds germinate?

Depending on what type of seeds you’re growing, you should see little seedlings popping through in a week or so. We grew marigolds, zinnias, and petunias, all things I love to have in the garden or in our window boxes.

The zinnias and marigolds came up pretty quickly, but we have to wait two weeks for the petunias… talk about an exercise in patience! I almost threw them out thinking they were duds. Don’t be like me; have patience… I hear it’s a virtue.

Remember, as your plants grow and you consider taking them outside to plant. You want to harden them off first (get them accustomed to the outside temperature). Read my full guide on how to harden off seedlings for detailed information.

You’ll do this by letting them sit outside during the day for a few days, and bringing them in at night. Then you should be able to safely plant them in your garden or container, like this DIY Self-Watering Planter!

Plant egg carton cups directly in the soil, or you can choose to break them apart to guarantee the root system is able to get through. 

What kind of seeds will you plant in your egg carton seed cups? I’d love to know what your kids think of this activity! Happy Gardening!