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Should You Plant Onion Seeds Or Onion Sets? How To Grow Great Onions!

The question comes up every single year among fellow gardeners – is it better to plant onion sets or onion seeds when growing onions?

The question certainly sparks quite the debate. And not just among those new to gardening, but seasoned veterans as well.

To be exact, onions can actually grow in three different ways: By planting a simple onion seed directly into the soil, by first growing a seed into a young transplant and then planting it into the garden, or by planting older but immature onion bulbs known as onion sets.

onion sets and onion seeds
When it comes to planting onions, there are 3 ways to grow a crop. From seed, a seedling transplant, or from immature onion bulbs known as sets.

So which of these three growing methods are the best? The simple truth is, all three methods have distinct advantages and disadvantages when it comes to growing onions. As for the best planting method for you, it really depends on how onions grow in the area you live. And to know that, you have to know the answers to the three important onion growing questions below:

  • What is your specific climate?
  • What type of onions can you grow in your area?
  • How many hours of daylight will your onion crop receive as they grow?

With those questions in mind, let’s first take a look at understanding how onions grow – and then how to find out which variety will grow well in your climate.

Should You Plant Onion Sets Or Onion Seeds?

How An Onion Grows

There are two important things to know about onions before selecting how you want to plant them.

One is knowing an onion’s complete growing cycle. The second is understanding that certain onions grow better or worse in different climates. First, let’s talk about an onion’s growing cycle.

Onions are a biennial crop. This means they grow, mature and finally produce a seed over a two year period, and not in a single growing season.

During the first year, an onion grows from a tiny seed into a bulb. If planted early enough from seed, the bulbs will grow large enough to be harvested and used that year as a smaller young onion.

seed head - biennial crop
An onion is a biennial crop. It will not produce a seed head until its second year of life.

But if the bulb stays in the ground over the winter, it will continue to grow in year two as the soil warms. It is in this second year that the bulb matures to complete its growth cycle. When this happens, it sends up a “bloom” and sets seed on the head of the flower. Thus completing its two year growing cycle.

Selecting The Right Onions For Your Growing Zone

Onion varieties fall into three distinct categories, short day onions, long day onions, and day-neutral onions. Each of these categories are based upon the climate, sunlight, and the days the onion will need to mature. Here is a look at each:

Short Day Onions

Short day onions are a warmer-climate onion. Because of this, short-day onions mainly grow in the south and southwest. Short day onions need around ten to twelve hours of average daylight to begin forming their bulbs.

Although short day onion varieties can grow in northern climates, the bulbs will never reach full maturity. Not in size, or in its flavor profile.

Long Day Onions

Long day onions mainly grow in northern climates. Planting of these onions can occur in the spring or fall from seeds, seedlings or sets. Long day onions need to get between 13 and 16 hours of daylight to begin maturing.

Long day onions cannot grow in southern areas because the daylight never extends long enough to form or mature bulbs from seed, sets or seedlings.

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Day Neutral Onions

Day-neutral onions are a bit different than short and long day onions in that they will form bulbs no matter the hours of sunlight they receive. These onions can grow anywhere except the extreme south, where it gets a bit too hot for them to mature.

Day-neutral onions need to go in the ground in warm climates in the fall, and early spring in the north.

Now that we have covered what onions can be planted where and when – it is time to tackle the question of what is best, planting onions sets or onion seeds? Here is a break down of each planting method, along with the advantages and disadvantages of planting each in your climate.

Planting Onion Sets, Onion Seeds, Or Onion Seedlings

Growing Onion Sets

Onion sets are small onions grown from seed the previous year. Instead of being allowed to mature, they are harvested as an immature bulb. Then, they are kept dormant until the following spring and planted.

So that all leads us to onion sets vs onion seeds and seedlings. And of course, choosing which is best for you. Here is a break down of each planting method, along with the advantages and disadvantages of planting each way.

Planting Onion Sets Vs. Onion Seeds & Seedlings – Choosing The Best Method To Plant

Growing Onion Sets

onion sets
Onion sets will give you a jump on growing larger onions, but varieties are usually limited compared to when growing from seed.

Onion sets are small onions that grow from seed or seedlings from the previous year. Instead of allowing them to mature, they harvest the small onions as an immature bulb. They are then kept dormant until the following spring and planted as a bulb to grow again.

Once planted, they mature into full-grown onions during their second year of growing. The advantage with onion sets is they already have a head start on their growth.

Not only can you harvest them sooner, it can also lead to harvesting larger bulbs. But, there is a disadvantage. With onion sets, you are limited to very few varieties of onions.

In the world of onions, there are hundreds of varieties available. Each with their own growing style and flavor profile. But with sets, you can usually only find them in only the common white, yellow and purple varieties.

So if variety is what you are looking for, growing from seed or seedlings may be a better choice.

Onion Seeds And Seedlings

The advantage of growing from onion seed is that you open yourself up to a wide range of varieties. Although you can direct seed into the ground in warmer climates, onion seeds take a long time to grow and mature.

That means for warmer climates, they need to be go in the ground in the fall or late winter. For northern climates, start seeds indoors 10 weeks prior to moving outside to transplant. In essence, this is the process of planting onion transplants or seedlings. And, it is a much better way to go when planting from seed.

One of the biggest disadvantages of planting seed is how long it takes to mature. But by growing seedling indoors or in trays, you allow your onions to get a head start. In addition, it makes weeding and bed care much easier.

Planting seeds directly outdoors in a large garden space can make it difficult to tell if what is sprouting is an onion, or a weed. But by growing transplants separately out of the garden, that chore is much easier!

Spring Planting vs. Fall Planting

One final subject that can play an important role in your onion harvest is the topic of when to plant.

Short Day onions (planted in southern and warmer locations) should always go into the ground in the fall. They can grow in the warmer winter and develop and be ready for late spring harvesting.

Long Day and Day Neutral onions on the other hand can go in the ground in the fall or spring. It is important to understand that a single season (spring to fall) of growing will produce smaller bulbs overall for harvesting – especially if you are growing from seed.

Seeds simply don’t have enough time to produce large bulbs when planted in the spring. Seedlings will give you a more sizable bulb with their head start with spring planting, but onion sets will give you by far the best chance at full bodied onions.

Fall Planting of Onions

Many gardeners in northern climates prefer to start some or all of their onions in the fall to guarantee larger onions. When planted in the fall, onions need to have at least 4 to 6 weeks of warm weather to establish in the soil.

As winter approaches, they go dormant until spring. They then spring back to life to complete their 2 year growing cycle. You can plant seeds, seedlings or onion sets this way. With seeds, the seeds should be in the ground at least 8 to 10 weeks before your average first frost date to get them large enough to handle winter.

For more on fall planting, check out our Fall Onion Planting article. Here is to growing your own delicious crop of onions this year – by seed, seedlings, or sets!

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