Skip to Content

How To Plant Onion Sets In Spring, And Why It’s Better Than Using Seeds!

When it comes to planting onions in the spring for a big summer harvest, onion sets are the way to go. Not only will it help ensure an earlier harvest, but one with larger, more flavorful onions too!

Onions can be planted and grown in a variety of methods. By seed, as transplants, or by planting sets.

Although all 3 methods can certainly produce a tasty crop, planting with sets (bulbs) has several advantages. Especially when it comes to planting onions in the spring.

Planting Onion Sets vs. Onion Seeds In The Spring

Growing from seed is certainly one of the most economical ways of all to grow onions. But it does have a few drawbacks. Especially for planting early in the growing season.

Unfortunately, in many growing zones, there simply isn’t enough time to grow onions from seed to full size.

planting onion sets
More than anything else, onions require loose, fertile soil that drains well. Soil that is too heavy or moist can stunt their growth and cause them to rot away before reaching maturity.

Onion seeds take a long time to develop and mature. In fact, many onion varieties can take as long as 5 to 6 months to develop large bulbs. In most climates, that means a frost or freeze is likely to occur before the onions reach full size.

The result is a harvest of smaller onions that haven’t fully develop their entire flavor profile. And that is exactly where onion sets come to the rescue!

The Power Of Planting Onion Sets

Onion sets are basically small, immature onions that have been grown from seed. The growing process is then halted and the onions are harvested. Not to be consumed, but to be planted again to grow to full size and flavor.

Because they have already aged a bit in the growing process, onion sets mature much more quickly than seeds.

In fact, instead of the 5 to 6 months it can take an onion seed to develop, onions sets can be harvested in as little as 60 to 80 days for mature onions. And even sooner for smaller spring onions.

But bulbs also have another big advantage over planting seeds – they are far easier to maintain! Onion seeds and sprouts are tiny. And they can quickly get lost and crowded out with weeds that sprout up along with them.

Anyone who have ever weeded tiny onions seed sprouts knows exactly how hard the task can be. But onion sets germinate fast with much larger sprouting stalks.

Not only are they easier to distinguish as onions, but they can compete against young weeds seeds much more successfully.

Selecting The Best Variety – Planting Onions Sets

Nearly all onion sets are sold as either white, yellow or red onions. There are a lot of varieties within each color of bulb, but in general, the flavors pan like this:

  • White Onions – White onions tend to be a bit more crisp, with a stronger flavor than yellow. They are one of the best choices for salsa and hold up to cooking well
  • Yellow Onions – Yellow onions are the workhorse of the three and are the most common. They have a good balance of flavor and hold up well in all kinds of dishes, or for fresh eating.
  • Red Onions – The mere color profile of red onions makes them perfect for using in salads, salsas and more. The can be a bit strong for some, especially if allowed to age. They make an excellent young onion too as their flavor tends to be crisp and still sweet.

Onion sets can usually be found at local nurseries, greenhouses and big box stores. But, they usually go pretty quickly, so get them early. You can also find them online.

We found the Stargazer Mix Assortment of Red, Yellow and White onions online, and have had great success with them. It’s nice to have all three varieties to grow for any need that arises for cooking or canning.

As a side note, smaller bulbs are better than large bulbs for planting. If onion set bulbs are overly large, they can easily bolt before they mature.

How To Plant Onion Sets

Onions will grow best in fertile, loose and well draining soil. As a root crop, the more loose the soil is, the easier they will grow and develop. Good drainage is important as it keeps the bulbs from rotting out in the soil.

Prior to planting, work in ample amounts of compost to the soil. We like to create a small trench a few inches deep, and then fill up halfway with an inch of compost.


Next, we plant our onions down into the compost so that the bulbs are about 1.5″ deep. This gives the onions plenty of good organic matter around their roots to power the bulbs. We then water the bulbs and cover with the remaining soil.

If you have exceptionally hard or clay-like soil, you can also amend your soil with a bit of sand. Sand can help improve drainage, and promote better bulb growth.

Spring Onions vs. Mature Onions – Planting Onion Sets

As for spacing the bulbs, it all depends how you will be harvesting your crop. Onions can be harvested early as smaller spring onions, or left in the ground to mature to full size.

For our spring onions, we plant each bulb about 1″ apart. Since we are always harvesting them earlier as smaller produce, they don’t require as much room to grow.

In fact, we start harvesting our spring onions as little as 4 weeks after planting. Not only are they delicious, it’s nice to have a bit of fresh produce so early in the growing season!

For onions we are letting grow to full maturity, we allow 4″ inches between bulbs at planting time. This gives them each plenty of space to mature and grow into full size onions.

Mulching, Watering & Fertilizing – How To Plant Onion Sets

Onions will not require much in the way of additional nutrients beyond the compost in the soil. They are low feeders, and too many nutrients can actually cause them to bolt early.

Check Out Our Latest Garden Podcast:

Mulch plants with a thin layer of straw or shredded leaves after planting. This will not only help conserve moisture, but help to keep weeds out.

One the bulbs have sprouted through, mulch to a depth of 3 to 4″ to help snuff out competing weeds. Onions will not require a lot of additional watering unless you experience long periods of drought.

You may want to water every few days the first few weeks if it does not rain to help the sprouting process. After that, as long as they receive a bit of rain every week, they should be fine.

Here is to planting and growing your own onion sets this year! Happy Gardening- Jim and Mary.

As always, feel free to email us at with comments, questions, or to simply say hello! You can sign up for our free email list in the subscribe now box in the middle of this article. Follow us on Facebook here : OWG Facebook. This article may contain affiliate links.