Onion Planting Choices – Seed vs. Set vs. Plants

Onions are a mainstay in vegetable production at all levels of  backyard growing,  community gardening and urban farming.  A producer has several choices of different forms that onions can be started from including seed, set or transplant.

Onion seed can be purchased from multiple suppliers and onions grow readily and easily from seed.  It is important to note that the onion (Allium) family seed is generally only viable for the year it is purchased and new seed should be purchased each year to ensure satisfactory germination rates.  Seed can be started in the ground early in the spring as well as under lights in a seed start grow station then transplanted in the ground in early spring when the soil is workable.  Seeds should be started under lights about 6-8 weeks prior to the transplant date and please note that onions are notoriously slow to germinate.

A common form of onion varieties that growers use for planting is onion sets.  An onion set is a live dormant onion bulb that was started from seed the previous year.  They are planted in the ground in early spring as soon as the soil is workable.

A third form of onion to plant is a purchased transplant.  These onion plants were grown the the prior year and come in banded bundles of 40-60 plants per bundle.  They are usually planted around early April in central Ohio.  They are a little harder to source than onion sets but generally will come labelled with what onion variety they are.  They may appear to be dried out but they are dormant live plants and need to be planted soon after purchase.


Each of these ways to plant onions can result in a good harvest and should be selected according to the management style and preferred variety of the grower.  The critical component for success is to know what day-length the onion variety is.  Onion size development depends to a great deal on the amount of day light they receive during the growing season.  The amount of day light needed by an onion variety to form a bulb is known as its day-length, and this varies depending upon what part of the country you grow in.  Central Ohio is a long-day onion location as we have a longer period of day light during the growing season as compared to the southern part of the United States.  Long-day onion varieties perform better here compared to short day varieties.  This is important when you make a choice of what form of onion you wish to plant whether it is seed, set or transplant,  that you pick a long-day onion variety.



Be careful when selecting what form of onion you wish to plant that you can verify if it is long-day vs. short-day to maximize production.

Illinois Extension Factsheet on Growing Onions


3 thoughts on “Onion Planting Choices – Seed vs. Set vs. Plants

  1. I realize this posting is nearly a year old, but it’s the latest post on onion sets I have found on your site.

    I am curious if there has been a study of the viability of onion sets, if stored in proper conditions. Would it only be 1 year, like seeds..?? Although I have had pretty decent luck with 2-3 year old onion seeds germinating.

    I’m just thinking of all of the sets that may possibly be thrown out at places like Rural King, that are sold in bulk. If a person would buy some at the end of the season, when they reduce prices to get rid of them, and select the one’s that have not started to grow, (Yeah, I screw my socks on in the morning, that’s how cheap I am,LOL…) then store somewhere cool until the following Spring, would they survive, or would a person just have a bag of mush somewhere along the line.

    Another question… Has anyone ever experimented starting onion sets in a green house environment, then, transplanting that onion set transplant into a garden..?? I’m just trying to find ways to get ahead of the game on weed pressure, and growing season. I have set onion plants from seed, then a few days later mulched them with leaves ran through a chipper/shredder, pretty much eliminating any weeds to contend with throughout the growing season, sans and occasional dressing up of the mulch. You just have to be pretty careful not to damage the small onion plants, when mulching. I’m thinking if started by sets, they may be a bit bigger, and not so likely to be damaged. I plan on experimenting with this, this Spring, as for starting transplants from sets, and see how it works.

    My big question is how long an onion set is viable. IF they would survive over the winter, it would make it possible to get a big jump on the growing season,in my mind.

    Dave Johnson
    Carroll, Ohio

    • Dave, I did some research and could not find an answer on viability of sets. I suspect it is not too long as once they have been put out into the store, and out of controlled storage, they start to degrade. I would be curious to see what your research on the topic leads to. Keep me in the loop on what you find if you give this technique a try.

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