How to grow onions from seed indoors?

Home gardeners may easily produce enough onions for the whole year. The most convenient method is to plant “sets” (little onions) in the spring. Seed catalogs, garden centers, and hardware shops all sell sets. In late April or early May, place the small bulbs about an inch deep in the garden, with four bulbs together, touching each other, and each bunch of four onion sets about 6 inches apart within rows. Eliot Coleman’s system simplifies planting, watering, weeding, and harvesting. In late winter/early spring, here’s how to grow onions from seed.


Types of Onions

Onions may also be started from seed inside in February or early March. The advantage to using seeds is that you have a greater selection of varieties, such as the big, sweet ‘Ailsa Craig’ and ‘Walla Walla’ cultivars. Checkerberry Farm in Parkman, Maine, organic gardener Jason Kafka, reportedly stated that his 3 1/2 ounces of ‘Ailsa Craig’ seed produced 8,000 pounds of onions on 0.4 acres.

‘Copra,’ for example, is a favorite hybrid among some growers, and it stores well. (‘Ailsa Craig’ and ‘Walla Walla’ have a limited shelf life.) ‘Marsi’ is a lovely red hybrid that stores till April. There are also an abundance of onion types that you can start indoors and plant in your garden when the time is right.

Starting Indoors

One way to start onions from seed indoors is to sow the seed in two rows, about a quarter-inch deep, in 4- x 6-inch containers filled nearly to the top with a seed starting mix. Keep the containers warm (near, but not too close to, the wood stove, or on top of the refrigerator, for example) and the seed starting mix wet. Don’t give up if the seeds take a few weeks to germinate.

Then in late April or early May, transplant the seedlings to a fertile, well-drained spot in the garden. Place four plants in each planting hole, as with sets, and distance each cluster of four onions approximately 6 inches apart.

During the growing season, keep the onion plot weeded and watered. Onions are shallow-rooted plants that benefit from an even supply of soil moisture. Their tops do not compete well with weeds, hence the importance of weeding—shallowly, to prevent injuring the shallow roots.

What number of onions should you grow? How many do you consume in a year? Most onions planted in a well-tended plot grow into large bulbs. Consider planting 400 or more seedlings or sets if you consume one onion per day (or some combination of the two). That much will need 50 row feet of garden area. Plant a little more than 100 seedlings or sets if you consume two onions every week.

Growing your own onions from seed is a terrific way to “think spring” in February, and the payback by July may be enormous and delicious.

How to Start Onions From Seed in Late Winter/Early Spring: Photos


To start onion seedlings indoors in February or March, fill a container nearly to the top with a seed starting mix and then make two furrows, about 1/2-inch deep, for the onion seeds. Put seeds into the furrows and gently cover with soil mix. Mark the container with the onion variety’s name. Place the container in a warm location.


Keep the young onion plants in a bright south window after the seeds germinate.

The seedlings might grow so tall that they flip over and make transplanting difficult.

Make a furrow in the garden in late April or early May.

Remove the onion seedlings from their container. (Newspaper on the bottom of this container kept the seed starting mix from being washed out the drainage holes.)

Separate groups of four seedlings carefully and, holding them lightly enough not to crush the tops, transplant them into the prepared trench, immediately covering the exposed roots with dirt.

Weeding is made simpler by planting onions in groups of four.

Onions may also be started from bought sets (little onions) that are planted in a furrow in groups of four, approximately 6 inches apart.

In the spring, onions grow. Keep weeds hoed when they are small, like those in this photo, because onions don’t compete well with weeds, and removing larger weeds can disrupt the shallow root systems of onions.

Related Questions

  • When should I start onion seeds indoors?

    Start onion seeds indoors around 8 to 10 weeks before your area’s final spring frost date. Follow the common best practices for indoor seed-starting: use a sterile seedling potting medium, keep the soil damp but not soggy, and provide at least 12 hours of bright light per day after germination.

  • Can I plant onion seeds indoors?

    When and How to Begin Within. Plant onion seeds indoors 8–10 weeks before transplanting them outside just before the average last frost date in your area. Seeds should be planted 14 inch deep. Onions require an open and sunny site, fertile soil, and good drainage.

  • Should I soak onion seeds before planting?

    While you may plant onion sets without soaking them, wet onions grow faster. To increase germination, moisten onion seed before planting. Soaking the sets in compost tea will provide additional nutrients and disease protection.

  • Is it better to grow onion from seed or bulb?

    Raising onions from seed is certainly the most cost-effective method. It’s also the sole method to develop rare or odd kinds. As soon as the soil can be worked in April or early May, seeds may be planted directly in the garden.

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