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How To Plant Onion Seedlings

I’m headed to the Seattle Tilth Early Spring Edible Plant Sale this Saturday, and ‘Walla Walla’ sweet onions and ‘Red Long of Tropea’ onions are on my list. I prefer to grow bulbing onions from seedlings because they bulb up more reliably than “sets” which are just small whole onions. Most gardening books recommend using a stick (sometimes called a dibble) to make an individual hole for each onion seedling. You then drop the onion into the hole and backfill soil around it. I find this incredibly tedious and instead plant my onions in a trench, which streamlines the planting process. Here’s how to do it:

Create a 3- to 4-inch deep V-shaped trench (also called a furrow) using a hoe or a trowel. Lay out the onions side by side against one bank of the furrow. I plant the seedlings only an inch or two apart. This spacing allows me to gradually thin out the onions and eat them at different stages. I thin out every other plant when they reach the scallion stage and again when the bulbs begin to form. I leave the remaining onions in the ground to grow into mature bulbs.

To plant the onions, simply draw the soil from one edge of the furrow over the seedlings roots, burying them and about the bottom 1/3 of the seedling. The seedlings will still be cockeyed at this stage.

Straighten out the seedlings by pushing the soil from the other side of the furrow in towards the middle. You want about two-thirds of each seedling to be above the soil line. This is not brain surgery or a precise science. If a seedling is buried too deeply, simply pull it up. If another needs to be buried deeper just hill a bit more soil around it.

Planting onions in a furrow also makes it easy to water them. Just put a bubbler attachment on the end of the hose and set it in the furrow. You can also water by hand by filling up the furrow repeatedly with water. Or, you can run a soaker hose or drip tape down the length of the furrow. The onions will push themselves up out of the soil as they grow (see top photo). Don’t hill soil up around the bulbs, as this prevents them from forming their papery protective outer layer. Onions, shallots, and leeks can all be planted this way.

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15 Responses to “How To Plant Onion Seedlings”

  1. 1
    Debbie Says:

    Great step by step … Thank you! I have always planted sets … your seedling plan looks good.
    Debbie :-)

  2. 2
    meemsnyc Says:

    This is such a great idea. Thanks for the tip!

  3. 3
    Gardener on Sherlock Street Says:

    What a nice sight. You make it look easy. Wish me luck!

  4. 4
    Jen Says:

    Awesome tute. I’m growing onions from seed for the first time this year and currently they aren’t looking to hot. We’ll see if they make it to the garden.

  5. 5
    Lindsey Says:

    Thank you Willi for awesome step by step advice. I have onions getting ready to plant and didn’t quite know how to tackle that! I agree with Jen, my seedlings look…sad. And anemic. I have followed directions to the tee and still, no dice.
    Maybe I’ll just get some seedlings and call the experiment done.
    I will be at the plant sale, too. All Hail Seattle Tilth!

  6. 6
    Wendy at Muck About Says:

    Great advice! Last year I planted sets, starts, and seeds at this time of year as an experiment. The starts outperformed the others. The sets bulbed-up small. The direct-planted seed made good green onions for summer, but didn’t make bulbs. I used to grow the starts myself, but I found I could buy good, inexpensive starts, so now I do that and save that room under the grow lights for other things. I like to grow Walla Wallas, and a storage variety like Copra or First Edition.

  7. 7
    Lorene Says:

    Hi Willi!!!
    Hope to see you at the Tilth Sale tomorrow… I’ve got my sights set on Purple Peacock Broccoli starts after tasting it in your Seattle garden last summer! Ummmmm…. come ON spring!

  8. 8
    Justine Says:

    Thanks Willi, I needed onion planting advice! I’ll be at the sale all day tomorrow, make sure to say hi!! If you can’t find me, send me a text.

  9. 9
    Andrea Says:

    Hi Willi!

    I attended your lectures in Boise a couple of weeks ago. Thanks for all the great information. With regard to this posting, can you plant leek starts in the same manner? Also, can they be considered scallions if harvested when young or are they quite different and not suitable for this type of harvesting? Thanks in advance for any info.

  10. 10
    Willi Says:

    Jen & Lindsey–Onion seedlings grow SO, SO slow. So don’t worry if you’re look pathetic. They’ll probably do just fine once you plant them. Just keep the soil moist. They have really shallow roots and dry soil sets them back.

    Wendy–I have done the same experiment and came to the exact same conclusions. I really need to do a storage variety. I love to grow Walla Wallas and Cippolinis and then I am out of space.

    Andrea–Thanks for coming to the Boise lecture! I thought that was a great event. You can plant leeks, onions, and shallots this way. Also, you can definitely harvest them when they are young as scallions. True scallions are Allium fistulosum and they don’t ever form bulbs, but you can always pull bulbing onions at any stage. That’s why I plant them close together. Then I can enjoy the onions at several stages.

  11. 11
    Elaine Says:

    I don’t have a lot of room left in my garden and would like to be able to interplant my leeks with other veggies. Do you have any suggestions? Maybe lettuces? I also have over-wintering garlic and onion that I was thinking of interplanting with greens. What do you think?

  12. 12
    Willi Says:

    Elaine–I often interplant my onions with lettuces and other lower growing greens. I use the onions to divide the beds into sections (i.e. last year I planted them crosswise across my beds on the ends and in the middle) and then plant the greens in the spaces in between.

  13. 13
    asebe Says:

    good idea

  14. 14 Says:

    Hello, just wanted to mention, I enjoyed this post. It was practical. Keep on posting!

  15. 15
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