How to Grow Onions from Seed

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Lynn Karlin

Janet Jemmott

Janet Jemmott

Photo: Lynn Karlin

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Like most gardeners, I started out growing onions from sets, which are small, immature onion bulbs. They were easy to grow, and I soon wanted to expand my variety horizons, but with onion sets, choices were limited. So I turned to seeds. Growing from seed let me pick varieties to suit my own needs or whims—such as the desire for an early-season sweet onion or a late-season keeper. Colors range from dashing purple to pure white and numerous shades of yellow. Shapes and sizes vary, too, from the bottle-shaped ‘Italian Torpedo’ to the plump perfection of ‘Ailsa Craig Exhibition’.

Most onion experts agree that, diversity aside, onions grown from seed perform better than those grown from sets. They are less prone to disease, they store better, and they bulb up faster.

I was convinced after my first year of growing onions from seed. The rewards were clear: a bin full of one of the most essential vegetables there is.

The long and short of day length
Onions need a long growing season, so place your seed orders early to get a head start. On a cold winter night, it’s great fun to browse through those seed catalogs piling up beside the sofa and choose a few new varieties.

When choosing seed, make sure to order types suited to your climate and zone. Onion varieties differ in the length of daylight and the temperature required to make a bulb. Short-day types are ideal for the South, where they grow through cool southern fall and winter months. They’re triggered to bulb by the 12 hours of sunlight that come with the return of warm, early summer weather.

Long-day onions are best grown in the North, where the summer daylight period is longer. These onions require at least 14 hours of light to bulb up. The plant grows foliage in cool spring weather, then forms bulbs during warm summer weather, triggered by the long days.

If short-day onions are grown in the North, they will bulb too early, then languish and never get to good size. (This, however, might be exactly what you want for pearl or pickling onions.) On the other hand, if long-day onions are grown in the South, they’ll produce lots of leaves, but no respectable bulbs.

Onions to cry for If you know your onions, your pantry can be well stocked with great varieties. Good storage bulbs are essential, and ‘Copra’ keeps well through the winter, even into mid-spring. Though ‘Sweet Sandwich’ and ‘Red Baron’ are good keepers, they are especially delicious eaten fresh. The portly bulbs of ‘Ailsa Craig Exhibition’ and ‘Lancastrian’ can be conversation starters and are just plain fun to grow.		Top row, from left: 'Red Baron', 'Copra'. Middle row: 'Sentinel', 'Evenezer', 'Sweet Sandwich'. Bottom row: 'Sweet Sandwich', 'Ailsa Craig Exhibition', 'Red Baron', 'Kelsae Sweet Giant'.
When choosing varieties, consider how you want to use onions in the kitchen, then pick the best for that purpose. For a good selection, try Johnny's Selected Seeds or Thompson & Morgan.
‘Copra’ – An early onion with medium-size, blocky globe bulbs and dark yellow skin. The rock hard bulb makes it unrivaled for storage. It also has the highest sugar content of the storage onions. 104 days to maturity. ‘Sweet Sandwich’ – Globe-shape and very sweet, especially after three months of storage. This onion is a long keeper and, as its name suggests, is excellent in sandwiches and cooking. 105 days to maturity.		‘Ailsa Craig Exhibition’ – A huge, round, snow-white, mild onion with straw-yellow skin. Matures well in northern gardens. Stores into late fall. 110 days to maturity. ‘Lancastrian’ – The foot­ball onion, averaging 5 lb. Crisp and sweet. Great for stuffing or onion rings. Short-term storage. 95 days to maturity. ‘Red Baron’ – A large, purple-red beauty. Also good for storage. 108 days to maturity. ‘First Edition’ – A medium-size onion with pungent flavor. It’s good for storage. 105 days to maturity.

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Comments (9)

chuck50 writes: I have successfully grown onions from sets, with this drought not many producers in our area are planting for sets. I am planting seeds for the first time, both in the garden and in a flat to use as sets. I will see which works best here in central Texas! Thanks for the article

Posted: 4:16 pm on November 5th

AmandaMomRoss writes: My onion starts shot up quickly and then flopped over and the foliage disintegrated away. I read that the planting depth could have been to shallow or its possible I overwatered. Any thoughts? BTW: thanks for the article! This is my 4th year gardening and I still feel like I know next to nothing! Glad to have found a website with decent articles.
Posted: 10:25 am on April 2nd

Ruth writes: Good one, myseasons. I haven't exactly flunked Onions 101, but I've never gotten higher than a C-. Onions are one of those tricky crops for me (along with eggplant and melons). But I keep trying, and I hope you will, too. Even undersized onions have a lot of flavor.
Posted: 9:11 am on January 20th

myseasons writes: I have failed Onions 101 three times now. With this instruction sheet I will try one more time. Wish me luck.
Posted: 11:03 am on January 19th

gardengrower writes: Thanks for the great information. I'm going to link to your article on my gardening blog. Can't wait to try my onions from seed this year, last year even my sets didn't do well.
Posted: 10:56 am on January 19th

HunkieDorie23 writes: I am starting my onions from seed this year and appreciate the pic. I already started with individual seed trays but will try the trays next year. I planted my onions in rows of two last year and it worked great. Planning to do it again this year.
Posted: 9:52 am on March 30th

maybee writes: We live in Mississippi and last early summer planted onion seeds. Went out today to start cleaning the old beds and we have about 20 green onions growing. What a surprise!
Posted: 4:55 pm on March 16th

lettucegrow writes: The best article on growing onions yet. I have done ok. A little less than ok actually. Small bulbs but still tasty. I want big bulbs! I'll be using your tips this year. Thank you.
Posted: 2:47 am on October 18th

Lorithyme writes: This is a great article - so complete. Thanks
Posted: 12:47 pm on March 14th

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