Understanding the facts when it comes to onion seeds vs onion sets can help you succeed this season
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If you are wanting to start growing onions, you will be confronted with two options. Do you grow them by using onion seeds or onion sets? It is beneficial to understand the differences involved in growing onions in each of these ways. Both offer their own pros and cons to the home grower and one may be more suited to your garden, your budget, or what you want from your onion harvest.
Even if you are an experienced hand at growing onions, it could help to consider trying things a bit different. Whether through mere curiosity or a strive to grow bigger onions, there are new techniques to try.
From a personal perspective, I have grown different varieties of onions for several years. The locations and final goals for these have ranged from cultivating them on an allotment for personal use to growing them in a productive walled garden in large numbers to be used by chefs. I have used both onion seeds and onion sets over the years and found that each does have their advantages and disadvantages.
Drew is a former professional gardener who specialized in growing vegetables and fruit. He worked in kitchen gardens for the National Trust in the UK for several years and then ran a productive walled garden growing vegetables, fruit, herbs, microgreens, and flowers for a high-caliber restaurant in England.
Onion sets are a popular way for home gardeners to grow onions, but what exactly are onion sets and how are they different from seeds or transplants? In this complete guide, we’ll explain everything you need to know about onion sets – what they are, how they’re grown, their pros and cons, and tips for planting them successfully.
What is an Onion Set?
An onion set is a miniature onion bulb that was grown the previous season. They are typically around the size of a nickel in diameter Onion sets form when onion seeds are planted more thickly than normal, resulting in crowded growing conditions. This crowding inhibits full size bulb development, so the onions stop growing early and form sets instead of large bulbs
The sets are harvested in late summer and then dried and stored in a dormant state over the winter. In spring, gardeners can purchase bags of onion sets from garden centers, hardware stores, seed catalogs, and websites. The sets wake up from dormancy when replanted and are ready to resume growing.
Onion sets are most commonly available in a few popular storage varieties like Yellow, White and Red. Shallot sets are also sometimes available. When planted in spring onion sets grow into mature, full size bulbs ready for harvest by mid-summer.
How are Onion Sets Grown?
Onion sets are produced commercially by growers who sow onion seeds very thickly in late summer, often in wide beds or rows. The crowded growing conditions trigger the onions to stop enlarging and form small bulbs in just 8-10 weeks.
In late summer or early fall when the foliage dies back, the sets are harvested from the soil After drying and curing, the sets are sorted by size, bagged up, and stored in cool, dry conditions over winter Larger sets may be replanted by the grower to produce seed. The smaller sets, around 1/2 inch in size, are sold the following spring for planting in home gardens.
Pros and Cons of Planting Onion Sets
Pros:
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Ease and convenience – No need to start seeds indoors, just plant the sets directly in the garden
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Earlier harvest – Sets form bulbs 4-6 weeks faster than plants grown from seeds
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More reliable crop – Sets practically guarantee a harvest, even for beginners
Cons:
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Limited variety options – Only the most popular storage varieties like yellow, white and red available as sets
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Smaller bulbs – Crowding as sets limits full size bulb development
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Tendency to bolt – Some sets prematurely form flower stalks instead of bulbs
Tips for Planting Onion Sets Successfully
Follow these tips to get the best results from your onion sets:
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Pick small sets – The smallest sets, about 1/2 inch wide, produce bigger bulbs than large sets. Avoid sets with green shoots emerging.
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Plant early – Get sets in the ground 3-4 weeks before last frost. Onions tolerate cool weather.
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Space properly – Allow 3-6 inches between sets depending on desired final bulb size.
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Plant shallow – Bury sets just 1-2 inches deep with tops slightly exposed.
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Fertilize lightly – Too much nitrogen causes excessive leaf growth rather than bulb growth.
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Weed diligently – Onions grow slowly at first and can easily become overwhelmed by weeds.
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Water thoroughly – Give 1-2 inches of water per week. Avoid waterlogging the soil.
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Cure well – Allow tops to die down completely before harvesting. Cure bulbs for long term storage.
Should You Buy Sets or Transplants?
Onion transplants offer another option, besides sets and seeds, for an early start on the onion growing season. Transplants are young onion seedlings started ahead of the season and sold in bundles.
Compared to transplants, sets allow earlier planting because there’s no threat of cold damage to the sets like there is with tender young seedlings. However, transplants generally grow bigger due to less crowding than sets experience.
For most beginner gardeners, sets are quicker and easier to plant directly without any advance preparation. So sets are great for beginners. But transplants offer more variety choices and potentially larger yields if properly handled and planted at the right time.
Storing Leftover Onion Sets
Don’t worry about leftover onion sets. Place any unused sets in a paper bag or stocking and keep in a cool, dry spot. Stored properly, sets can remain viable for several months. Replant leftover sets in late summer or fall for a second onion harvest.
Enjoy the Convenience of Onion Sets
Onion sets offer gardeners an easy, low effort way to grow a crop of onions. Just poke them into the ground in early spring and wait for the delicious bulbs to size up. Though limited in variety, their convenience makes sets a great choice for the impatient or busy gardener. With the right planting and care, onion sets will provide a bountiful harvest.
Sowing onion seeds = more options and bigger bulbs
Onion seeds can be started early in the year, or even at the end of the year. It has become a tradition for many growers to sow their onion seeds straight after Christmas ready for the seedlings to be planted out in spring when the soil warms up. This is often only an option if you have a good heated greenhouse.
Onion seeds can be sown indoors in late winter, sown in trays or modules at temperatures of 50-61˚F, and then planted out mid-to-late spring after a period of hardening off. Onion seeds can also be sown directly outdoors into a finely raked bed in the spring.
Pros of growing onions from seed:
- There is a wide variety of cultivars available to choose from.
- Onions grown from seeds are less prone to bolting.
- Seeds are a lot cheaper to buy than sets, so a more budget-friendly option
- The sowing times are more flexible.
- Growing from seed tends to result in large onions.
Cons of growing onions from seeds:
- Growing onions from seed is more labor intensive.
- Requires focused sowing, watering, and planting out.
- Needs materials – compost, pots, and a heated indoor space or propagator.
- Onions grown from seed can be more susceptible to disease.
The experts at Amateur Gardening recommend: Sow large varieties in cells, thinning down to one seedling per cell. Onions can be sown cold, but a temperature of around 50˚F will move growth along more quickly.
Onion seeds should be sown indoors in winter in trays or modules( credit: Future/Amateur Gardening)
The simplicity of planting onion sets
Onion sets are part-grown onions that have been started into growth from seed and not allowed to grow to full size. Its first-year development has been stopped and the small, immature bulbs dried off and stored through winter. Planting onion sets is commonly done in early spring, though there are some varieties that can be planted in fall. To plant onion sets, simply push them into the soil 4in apart in your veg patch or raised garden bed so their tips are just showing.
Graham Rice, expert for Amateur Gardening, claims the main benefit of onion sets is that they’re very easy.
It’s hard to mess up and you have to do something seriously wrong to get no crop, he adds. Plant them in early to mid spring and away they go. You bypass the tricky seed germination stage – all that’s needed is a little bit of watering and weeding, and you’ll be harvesting onions from the middle of summer.
It’s worth remembering that onions grown from sets tend to produce slightly smaller bulbs than those grown from seed, but this is a small price to pay when you consider how much easier they are.
Pros of growing onions from sets:
- Sets are easier to grow, they just need to be pushed into the soil.
- They are less prone to disease.
- Sets allow for a good crop even in poor soil types.
- Onions grown from sets are ready to harvest earlier and can still mature even in a short season.
Cons of growing onions from sets:
- Only a limited range of onion varieties available as sets.
- Sets are more expensive to buy than seeds.
- Onions grown from sets are more prone to bolting.
- Sets can come with more critical dates for planting.
Onion sets are quick and easy to plant( credit: Gettys/Melena-Nsk)
Onion sets can also be started indoors early and Bob Flowerdew, Amateur Gardenings organic expert, advises that starting off onion sets in small pots or modules can be advantageous as they are easier planting out than a seedling started from seed.
Onion sets are planted later in spring than seeds are sown – and that means sets can provide a good back-up alternative to failed sowings. I had an experience where my onion seeds were not germinating well enough and, in order to have a large enough harvest of onions that I required, I still had time to get onion sets and plant them to supplement the number of seedlings I had to plant out and grow on.
How you grew your onions can impact their harvest size( credit: Future)
Planting Onion Sets: What to Watch Out For
FAQ
Are onion sets just small onions?
Onion sets are mini onions, baby onions. A stage between a seed and a fully grown onion. They have been grown by somebody else from seed, before they arrived at your place. I’ve added the picture above to illustrate the different stages. The seeds, the baby onion and the full-grown onion.
What is the difference between an onion set and an onion start?
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.
How do you use onion sets?
Onion sets are very easy to plant. Simply push the onion set into the loose soil up to the neck, barely putting the onion bulb under the soil. The pointed or sprouted end should be sticking up out of the soil.
Are onion sets worth it?
Planting onions from small bulbs or “sets” is not the best way to grow large onions for storage. Plants grown from sets often begin blooming in mid-summer and stubbornly refuse to stop. Once that happens, onion bulbs don’t increase much in size. This happens because onions are biennials.