Planting Onion Plants

Now that you’ve done all the hard work, it’s time to plant! Be sure to remove all weeds from the soil bed before planting and have some straw ready for mulching after you plant.

NOTE: This is part 4 in a series of 9 articles. For a complete background on how to grow onion plants, we recommend starting from the beginning.

When to Plant

Plant your onions 4 to 6 weeks before the last estimated spring freeze. (Your agricultural extension service can tell you when that is.) You can also plant onion sets in the fall to get a head start on the spring season. They will go dormant over the winter and reemerge in the spring.

Fertilize First!

As mentioned in the Soil Preparation section, fertilizer goes in first—before planting. Do not sprinkle additional fertilizer over the top of the trench at planting time.

Depth/Spacing

Plant the onions 6 inches from the edge of the trench on both sides of the trench (see the Soil Preparation article for trench details). DO NOT plant the onions in the trench! Leave a 2-inch margin between the onions and the outside edge of the "hill."

Plant the onions 1 inch deep but no deeper—doing so will inhibit their ability to bulb.

If you want the onions to grow to maturity, space them 4 inches apart. If you prefer to harvest some earlier as green onions, space them 2 inches apart and pull every other onion during the growing season, leaving the rest to grow to full size.

When planting several rows of onions, leave 16? between the outside edge of one bed and the outside edge of the next. The spacing from the center of one fertilizer trench to the center of the next should be 36 inches.

Planting Tips

  • Plant the transplants with the root side down and cover with 1 inch of soil, no more.
  • Water thoroughly but not often, as onions are somewhat susceptible to rot.
  • If desired, mulch with just 2-4 inches of straw (or untreated grass clippings) and be sure to keep the mulch away from the emerging onions. When your onions begin to sprout, pull the mulch away a little further and increase the depth of the mulch layer to 4-5 inches to keep the weeds out.

In as few as 4 weeks, you can harvest green onions; in about two to four months, you will have full-grown onions!

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Tools & Supplies for Onion Plants