How to plant onions, scallions, and leeks | The Old Farmer's Almanac

Crying for Onions

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George and Becky Lohmiller
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Follow this advice on planting onions in different regions and different types of soil. Also, see our gardening tips on the aromatic leek!

Planting Onions

Onions are one of the most widely cultivated vegetables in the world. In ancient times, they were a dietary staple because they are easy to grow and can be stored for a long time.

  • Onions do best when started in cool (not cold) weather. In cold-winter areas, plant onions in spring. In mild areas, you can plant them in fall or winter. See Best Planting Dates chart.
  • Onions can be raised from seeds in areas with a long growing season, but most gardeners prefer to plant onion sets—tiny onions that were started from seeds the previous season.
  • To grow large onions, plant the sets four to five inches apart in a row or bed.
  • If you love scallions, or green onions, plant the sets closer together and harvest these immature onions as you thin the plants. See our Plant Companions article and  our Plant Companions chart to find out where to plant onions in your garden.
  • Onions grow best in rich, loamy, well-drained soil. Improve sandy or clay soil with compost or peat moss, and add a standard application of fertilizer before planting. A light application of mulch will help keep the weeds down and conserve soil moisture.

Why the crying? The pungent odor released when onions are cut is caused by allyl, a natural sulfurous oil that quickly vaporizes and can bring a person to tears. Plunging an onion into boiling water for a few seconds before you peel it will neutralize the allyl, or you can peel it under running water to dilute the irritant—with wet hands and dry eyes.

For more details and advice on planting onions, visit our Onions page!

Planting Leeks

Leeks are closely related to onions, but they don’t have a bulb. Instead, leeks form a thick, fleshy stem at the base of their coarse leaves. Leeks have a more subtle, slightly sweet flavor versus the more pungent onion—and they're also packed with nutrients and health benefits. Here's how to plant:

  • The cultural requirements for leeks are the same as for onions. In northern areas, start leeks indoors in flats.
  • Start leek seeds indoors 12 weeks before the last frost. See Best Planting Dates chart, based on your last spring frost date.
  • Plant the seedlings as soon as the ground can be worked.
  • Dig a trench 1 foot deep and 1 foot wide. Fill the bottom with a 5-inch layer of compost and transplant seedlings into holes 6 inches apart.
  • As leeks grow, gradually fill in the trench with more soil, keeping the tips of the plants exposed.
  • When the plants are six to eight inches tall, cut them back to three inches and transplant them to the garden.
  • Mound the soil as they grow, so the lower five inches of stem will become blanched; or plant the leeks in a trench five inches deep and fill it as the plants mature.
  • As with onions, leeks can be harvested when they are young, or you can leave them in the ground until frost. If mulched with a heavy cover of hay, leeks can be harvested well into the winter.

Wondering what to cook with leeks? Leeks are an appetizing and healthy addition to many meals, but if you wish to really taste the leek flavor, try Cock-a-Leekie Soup. We also love this Leek and Herb Quiche.

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