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

Are you growing onions from onion sets?  Do they send up seed stalks or do the tops fall over earlier than you think they should?  Do you get onions about pearl onion size, but want bigger ones?

With an understanding of how onions grow it’s possible to get better results.

Understanding What an Onion Set Is

Onion sets are small onion bulbs produced from seeds the previous year. Since they’re last years onions, their “job” this year is to make seed. That makes them very prone to stalking and setting seed.

Mainly Sets Offered in Local Feed and Seeds

When I first started gardening 33 years ago, sets and seed were the only way onions were offered by the local feed and seed stores.  Because of that, I thought they were the only ways onions were grown.  And since I thought of seed as being too difficult, sets seemed the easy way to go.

It was only after about 5 years of growing onions from sets that I discovered you get bigger and better onions with transplants. (Transplants are a small onion raised from seed the same year you plant them.)

What Accounts for Most of the Problems Gardeners Experience with Sets

I never remember seeing any information along with the onions in the store other than the price.  Most of the time seed catalogs give information about the sets they offer. But, if you don’t know much about onions you don’t pick up on the information you need.

And this lack of information (or knowledge) probably accounts for most of the problems that people have when growing sets.

Understand this Fundamental Onion Fact

To form bulbs, onions require a certain number of daylight hours.  Different varieties require different day lengths. And the North gets more daylight than the South.

A variety that takes 14 to 16 hours of daylight before it can start to bulb can only be grown to maturity by northern growers.  They are called Long Day Onions.

Intermediate-Day Onions start the bulbing process when daylight reaches 12 to 14 hours. These onions will perform well in most parts of the country except the extreme southern part.

Varieties of Short Day onions start bulbing when daylight reaches 10 to 12 hours.  These varieties are the ones that Southern gardeners must have to be successful.

A gardener in the South who never gets more than 10 to 12 hours of daylight will not be able to get large bulbed onions from varieties that require more than 12 hours of daylight to bulb.

Dixondale Farms in Texas, probably THE largest supplier of onion transplants, has a nice map on their website that shows this.

Now you know why it’s important to know if your sets are Long Day or Short Day Onions.  You want to make sure you have enough daylight hours to bring them to maturity.

The Size of the Onion Set is Important

When you buy your sets separate them into small and large.  The ones that will make the larger onions are about the size of a marble or a dime.  Anything larger than that will produce only spring onions.

Planting Depth is Important

Plant your onions about one inch deep.  This is true for sets and for transplants.  If you plant too deeply the onions won’t bulb and you’ll just get a straight stalk.


More space equals larger onions.  So if large is your goal you will want to space your onions at least 3 or 4 inches apart.

When to Harvest

  • Onions can be pulled and eaten anytime you want.
  • When onion tops fall over by themselves, they’re finished.  They won’t grow any more.  Harvest and eat or harvest and cure.
  • If the onion makes a hard/hollow stalk and forms the bulb which will become the seed head, they are finished and won’t grow much more.  Harvest and eat.  They will not cure.

Plant Early

Plant early enough to give your onions time to develop good roots and grow some before daylight hours trigger bulbing.  Otherwise, you’ll get very small onions.

If You Plan to Save Seed

If your onions are hybrid then the seed will not come back true.  In other words, you may get an entirely different onion than the one from which you harvested the seed.

Open pollinated and heirloom types breed true.

Know if your variety is hybrid or OP/heirloom.

Final Words

Weather and rain can also effect bulb size. You can’t control that. But armed with the information above you should be able to get much better results and some good sized onions from your sets.


More Posts about Onions:

Growing Onions

How to Have Garden Onions April Thru January

Onions – More Reasons to Plant

Bunching Onions – A Perennial Scallion Patch


All content including pictures is copyrighted by TendingMyGarden.com.  All rights are reserved.


  • Thanks for all your great advice on growing onions. I am very excited to be trying them this year.

    When are onions “spring onions”? I am in zone 5 so I can’t plant as early as you do so my onions haven’t gotten very big yet.

    I just reread your post on scallions and was wondering if you have ever grown Egyptian walking onions? I got a bunch from my aunt a few years ago. They develop new bulbs on the top of the green stalks which causes the stalk to fall over and then the bulbs take root. This causes the onion to “walk” across the garden. I prefer the more mature stalks to eat because it is less pungent than the smaller stalks. They taste like a scallion or geeen onion. It is an interesting plant to grow and has filled in at a moderate rate in my garden.

    I hope to use it more this year now that it is more established.

  • Hi Christine,

    Glad you’ve enjoyed the onion posts. You’ll love having onions from the garden.

    Onions are considered spring onions when they slightly bulb rather than just having a straight stalk like scallions. There’s a picture on the post https://tendingmygarden.com/onions-more-reasons-to-plant/.

    I had Egyptian walking onions years ago when I first started gardening. I didn’t really know what to do with them back then. I don’t remember now if I pulled them up or if they just “disappeared”. They really are something that is nice to have,

    Onions have so many wonderful health benefits too. So do use your onions as often as you can.

    Thanks for commenting Christine. Let me know how your onions do. And by the way, did you plant from sets?

    Warm regards,

  • I planted seedlings from Dioxandale Farms per your recommendation 🙂 Also hoping the onions will help deter striped cucumber beetles. I had a battle with them last summer and they won. I had to give up on zucchini and cucumbers earlier than I wanted too.

  • I think you went the right way with seedlings Christine. They make for better onions.

    I don’t know for sure if onions help deter the striped cucumber beetles or not. I had onions planted with squash last year in hopes of deterring the squash bug. Seemed like it was working for a while, but they finally came in numbers just like the cucumber beetles. And I do think that those beetles cause the cukes to give sooner than they ordinarily would.

    In past years when I just have not had time to check for squash bugs, I just didn’t grow squash. Of course they get on cucumber too. Oh well.

    Let me know if you think the onions help prevent them in your garden.


  • I planted onions last summer and left some in the ground over the winter. We live in Zone 4, so are these onions edible this spring? We weren’t sure because of the severe cold we experience during our winters. Thanks much.

  • Hi Shelli,

    Indeed they are edible. Leaving some onions in the ground over winter is what I call my backup onions. Some tiny transplants that I plant in the spring never fully mature. I leave them if they are small and some “hide” and I miss them anyway. I’m always so happy when I have them for spring onions in January and February.

    Of course, I don’t live in zone 4, but you can tell by looking if the onions are good. If they look like regular spring onions — they’re edible. 8)

    Let me know how delicious they are.


  • Question:
    I purchased what was marked Dill at Lowe’s and now I have a very tall bunch of onions bunched in one tight plant. The greens are not hollow like green onions but more like grass. I can break one off by itself and use in cooking although they don’t have the strong taste of onions. Can you tell me what these are called?

  • Hi Billie,

    From your description my guess is that you have chives. And you probably have regular chives which in my opinion look more like grass than garlic chives. The “grass-like” leaf is round. I have garlic chives. Their leaf is flat.

    Bunching onions would have met the description had you not pointed out that the greens are not hollow. (Bunching onions have hollow stems.( See my post on bunching onions. )

    Best regards,

  • I was wrong about the tag saying the plant was dill. It said chives. But the “chives” are as big as a regular green onion, maybe bigger. Is this size normal for garlic chives? Also,they are all connected at the bottom but easily can be pulled apart one by one and the others are still growing.
    Thanks for your help. We are in zone 9.

  • Billie, my next guess would definitely be bunching onions. Bunching onions do have the slightly hollow stem however.


  • Thanks Theresa – – the spring onions turned out beautifully! I plan on doing that again (purposely) this year.

  • Hi Shelli,

    I was delighted to hear how beautifully the spring onions turned out!

    The garden will show you lots of ways to get more treats like this.

    Thanks so much for letting me know — the rest of the story.


  • Hi Theresa,
    I’ve just come across your website and found so much information on onion growing it’s amazing, I guess that’s what you get with 35yrs “service”!
    I wondered if you could give me some advice, I’m a first time gardener this year and my onions (hercules) planted in Scotland UK in early April have started rising out of the soil and therefore falling over, the bulbs are not large (2inch), is this because they are ready for harvest or can I push them back into the soil and if so will they keep growing?
    Many thanks in advance.

  • Welcome to TMG Kirsty! And yes, I do have lots of information on growing onions and I think you will find it help to review all the various post on onions.

    Onions start to rise out of the soil as they bulb. The tops fall over when they’re finished growing. They will not grow anymore.

    Small bulbs can be caused by not enough time in the ground to grow before bulbing starts or planting too deeply. (One inch is the proper planting depth. No more.)

    If the bulbs are really small, you could cure them and replant to use for “spring” onions this fall and winter.
    Hope this helps.
    Good luck with you garden!

  • Hi, I am trying to understand if I can plant onions in the fall, in Ohio… And if I can, do I plant seeds or sets? I’m not sure if it is too late or not…

  • Hello Theresa,
    Thank you for a wonderful article on Onions!

    I am about to plant a bag of sets that i bought a quite a few weeks back now and “didn’t get round to planting”.

    I am in Zone 5 the date is May 21st – will i only get spring Onions or could I have caught things in time..



  • Jason,
    I’m not sure what conditions are in zone 5, but overall you’ll probably able to plant later than what gardeners in zones further south would plant. Even if you’re a little late for the ultimate best results, it’s still worth a try. My quess is that you will probably get some nice sized onions and some spring onions as well.
    Good luck!

  • Hi Theresa,
    Quick question on onions…you may remember I use row covers nearly all season. I try to squeeze in plants everywhere I can, so typically I’ll set my onions in along the sides of the beds to take up that narrow space between the frame of my raised bed and the neighboring plant.
    (in a neat row)

    In the bed where I have (tall) fava beans growing, I never had a cover on this bed and the onions are planted along the side. In other covered beds the onions did not get nearly as large as with the open bed. The row cover is a special breathable fabric for growers and allows 70% light through.

    I was so careful not to plant the transplants too deep (probably not even 1″ deep). So my question is I’m wondering if the onions would have done better in an area w/o the cover to receive more light? If I planted approx 300 transplants, I only got around 100 to bulb nicely.

    From all your experience, what do you think went wrong?

    Thank You


    Ps. also, would it have any effect on the onion if I trimmed some of the fallen greens back…would it stunt the plant for example?

  • Jim, I agree with you that the first thing to look to is definitely the lack of that 30% extra amount of light. Variables can be many in any growing situation, but my first bet would be the lack of light.

    The fact that you get such good results on most of your things using row cover consistently is rather amazing. Light and good air circulation are two of nature’s requirements that we all have to pay close attention to. Any kind of cover cuts back on both.

    You already have a good indication from the ones you planted with the fava beans. Every season that you conduct another experiment, you’ll be closer to learning more of what your onions want.

    Regarding trimming your fallen greens on the onions: If you plan to cure and store the onions, I would NOT trim back the green top; but rather allow it to die back and dry totally in the curing process before trimming. Your onions will cure better that way.


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