Time

4 to 6 weeks.

Complexity

Beginner

Cost

$5-$30

Introduction

Many gardeners purchase small onion bulbs, aka onion sets, in early spring to plant directly in the ground. But growing onions from seeds is just as easy and gives you a lot more choices.

Once you've grown one variety, use the same method for other kinds, like red, white, yellow and bunching onions, and even shallots.

While you can sow onion seeds directly in the garden, starting them indoors permits a faster start in the spring. It doesn't take long and doesn't require expensive equipment.

For the cost of the seeds, plus a seed-starting mix and a grow light, you can do it for less than $30, a little more if you purchase reusable flats instead of reusing containers you might already have. Your grow light is a one-time investment, and you can re-use flats for seed sowing. So once you start sowing seeds indoors regularly, your costs are the price of the seeds plus the seed-starting mix.

onion seed packets
Carol J. Michel For Family Handyman

Tools Required

  • Clear cover
  • Container for seed sowing
  • Indoor grow light
  • Scissors
  • Spray bottle (optional)

Materials Required

  • Onion seeds
  • Plant labels
  • Seed-starting soil mix

Project step-by-step (6)

Step 1

Prep the soil for seed sowing

  • Fill your container with the seed-starting mix and wet it down thoroughly.
    • Seed-starting mixes are usually dry out of the package. I often put some in a plastic tub, add water and stir the soil so it absorbs water faster.
  • Add moistened soil to the container. You don’t need a lot — 1-1/2- to 2-inches of soil will work just fine.
    • The best option for growing onions indoors is to use a sturdy container with adequate draining holes. If reusing a plastic container without drainage holes, carefully cut or punch small holes in the bottom.
Step 2

Scatter onion seeds on top of the soil

  • Onion seeds barely need to be covered, so scatter them across the surface of the soil, then gently press them into it.
  • Sprinkle more seed starting mix on top and lightly spray the surface with water, using a spray bottle or a sink spray nozzle.

seeds scatter on soil
Carol J. Michel For Family Handyman

Step 3

Add a label and cover the container

  • Write the variety of onions on a label and stick it in the container.
  • Cover the container with a clear plastic lid and place it under the grow lights.
    • If using a recycled plastic container with no lid, put it inside a plastic bag. You don’t want the surface of the soil to dry out.

onion seedlings just coming up
Carol J. Michel For Family Handyman

Step 4

Remove cover when seeds germinate

  • Once the onion seeds begin to germinate, remove the cover while keeping the seedlings under the grow lights.
  • Water gently as needed to avoid washing out the seedlings.

Onion seedlings, a little bigger.
Carol J. Michel For Family Handyman

Step 5

Trim back seedlings, as needed

  • Once seedlings are four to five inches tall, cut them back to two to three inches.
    • Those cuttings are edible! Use them the same way you would chives.
  • Continue to water your seedlings, as needed.

onion seedlings with trimmings next to them.
Carol J. Michel For Family Handyman

Step 6

Harden off seedlings, then plant them in the garden

  • Plant onion seedlings in the garden once you’re about four weeks away from your predicted frost-free date or later. Be sure to harden them off first. Hardening off seedlings is when you gradually acclimate them to the outdoors. The process usually takes around two weeks and helps to prevent shock while the seedlings get used to sunlight, wind, and temperature changes.
  • Gently remove and separate the seedlings, then plant about one inch deep in a sunny location. Space them according to the directions on the seed packet.
    • Bunching onions can be spaced one inch apart. Bulb-forming onions generally need to be three inches apart.

some onion seedlings ready to plant
Carol J. Michel For Family Handyman

FAQ

How do I know when onions are ready to harvest?

When the tops of onions are yellowing or start to dry out, it’s typically a sign that they are ready to harvest.

How much time does it take to grow onions from seed?

Onions usually take around 100 days or about four months to mature from seeds.

Author
Carol J. Michel
Carol J. Michel is an award-winning author of five gardening humor books and two children's book. She has a degree in horticulture from Purdue University. Carol began writing about gardening on her eponymous website, which led to numerous magazine articles, her books and a podcast called The Gardenangelists. She started gardening as a toddler follo...
Read More
Carol J. Michel