Onion Sets – Reasons to Grow Them and How

Ever order too many onion transplants and wonder where in the world you were going to plant them all?

Ever start onion seeds and have a lot more come up than what you anticipated and wonder how you’ll use that many onions.

Or maybe you’re like me and just want another way to add to your strategy to insure having some form of home grown onions all year.

Here’s a way to use your excess seedlings or to use as part of your strategy to have onions all year.

Grow your own onion sets.

Chose the method that’s most convenient for you:

  • Direct seed into a small area of the garden at the time you would usually plant. Sow thickly so that the bulbs will not be able to expand. They’ll “finish” as very small bulbs.
  • Or start your seed in a jug bottom or flat about 6 to 8 weeks before you would plant onions outside. When transplanting to the garden plant close together.
  • If you buy transplants, use the smaller ones in the bundle to plant as you would your own seedlings as mentioned above.

Why They’ll Make Sets

When you plant onions really close together is stops their development. They’re unable to expand and they’ll mature earlier in the season. You can cure them just like large onions, hold, and replant again at the appropriate time in your area.

Here in zone 7, I replant again in August or September for spring onions in the fall and sometimes through the winter. (Yes, even when we have snow!)

Since Virginia is just about in the middle of the continent, I can grow long day onions (usually grown in the North) and short day onions (usually grown in the south).

Thus, if I’m growing a long day onion that’s a storage onion, like Copra, I could hold these sets over until next March and plant out in the garden.

If I were growing short day onions, they’d have to be planted in the fall since they wouldn’t keep through the winter for spring planting.

How Close is Close?

Good question.

I’m going to plant some onions especially to produce sets in a small area of the garden this year. I’ll try two spacings for each type of onion.

Long day onions that are considered good for storage, I’ll plant 1/4 inch apart and some 1/2 inch apart. These are the sets that will store well. I’ll hold them over until next spring. I want these to be very small; about dime size. That small size will produce the biggest onions when planted the following spring.

Short day onions: I’ll plant some 1/2 inch apart and some 1 inch apart. I have a feeling that might be a waste of space, but I want to see what they’ll do.  And since I want them for fall-planted spring onions, it won’t matter if they get too big.

Testing various spacings this year should give me a good idea of how I can be even more successful growing sets in possibly even less space in future years.

How I Came By Sets Previously

Out of about 1500 onions, I always get a couple of dozen that don’t mature properly.  So they end up as sets which I replant in the fall.

Final Thoughts

If you have an excess of onion seedlings and know you can’t use that many onions when they mature, growing sets is a great way to make them last to a time in the future that you can use them.

Or, if you’re an onion lover like me, and the goal is to have some form of home grown onions during every month of the year. Growing sets for replanting is just one more way.


A Few Other Onion Posts:

Onions- Starting Seed – Planting to the Garden – Leeks

Onions – Tip – What to do with the Small Ones

Onions Plants – A Bonus Can be Green onions in Winter

Onions – Why Grow A Lot?

Onions – Starting from Seed is Easy and Economical

Onion Sets – What You Need to Know to Get Better Results

Growing Onions

Bunching Onions – A Perennial Scallion Patch

Onions – More Reasons to Plant

How to Have Garden Onions April thru January


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  • Thanks, Theresa, this came just in time! I’m going to start some wintersown onions this morning and yes, have more seed than I need and some left over seed. I will try to make some of my own sets for next fall (can never find them in the fall) and winter.

    I wondered how sets were made? How do you store them? Same as regular onions?

  • So, you plant your sets close together, to keep them little then just space them out in the fall to produce full size onions, or are you harvesting them as little “sets” in June-ish, then replanting them in the fall?

  • Thank you Theresa!

    I had been buying onion sets online for the past couple of years, and have never had any luck — they really did absolutely nothing. The bulbs I had been receiving definitely were not near dime-sized – more like needles, and they looked pretty dead on arrival (although the seed company assured that that was normal.)

    After having read your related articles on growing onions, I also may have been planting too deep.

    I do not recall seeing onion transplants available at any garden centers or growers around here, but I’m interested in trying the transplants. Would you recommend the Dixondale Farms that you referenced in another article?

    As always, many thanks!

  • Betty, store your sets like you would your regular onions. Cool and dry.

    When you plant the onions (seeds or seedlings a/k/a transplants) they will not yet be sets. The end result at harvest will be sets.

    You plant the onion seed or seedlings close together so they will not develop into full size onions, but rather into small bulbs called sets.

    When the seed or seedlings “finish” it will be about June. (It could be before because they should finish up more quickly than your full sized onions.) Depends on when you plant. When you harvest them they will be “sets”.

    We (in Virginia and North Carolina) will not get full sized onions when we plant those sets in the fall. We’ll get “spring onions”.
    (Not enough light in the fall.)

    Picture an imaginary line from San Francisco and Washington DC. Most folks north of that line grow long day onions because they require 14 to 15 hours of daylight before they can start to bulb. In other words, in general those South of that line are not going to get storage onions like Copra to maturity because there is not enough light. Most storage onions are long day onions.

    Thus, most folks south of the line grow short day onions which only require 10 to 12 hours to bulb. It just so happens that short day onions usually are not storage onions. In general they keep about 3 months. I’ve had some keep 5 months.

    There is also an intermediate Day onion that starts bulbing when daylight reaches 12 to 14 hours.

    If you could find a good storage onion that is an intermediate day onion (I don’t know one), then you (in North Carolina) may be able to grow sets and then hold them over until the following spring, plant, and get full sized onions.

    I hope this answers your questions. It’s easy once you “get it”, but until then it can be a bit daunting. I’m writing a book (or maybe an ebook) that will give a lot more detail.
    In the meantime, ask again if I have not clarified for you.

    Anne, when you buy sets online or in the local seed store, there will always be ones that are not any good. Usually those are hollow and dry rather than firm.

    Dixondale Farms folks are good people. Keep in mind they are conventional; not organic. Some of their advice is off key for folks like me, but they’re good to deal with.

    Also, you can ask in advance what varieties come from Monsanto (in any shape, form, or fashion) and they’ll tell you. That way you can plan your order accordingly.

    In addition to getting off to a good start with transplants from Dixondale, why not buy a package of onion seed and make this an experimental year for onions. Once you get the hang of growing from seed, you’ll have your own transplants.

    Let me know if you need more help.

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