How to Plant Onion Sets (to grow BIG onions!)

I’m going to show you how we plant onion sets and then dig up big onions when they’re ready! Growing onions overwinter is a great way to keep gardening all year long. Onion sets are planted in the Fall and then harvested in the late spring.

Why We Like Onion Sets Better Than Seeds

Depending on personal preference onions can be grown from seed, transplants or sets. Personally we prefer onion sets for a couple reasons:

Onion sets are much larger than a seed and less fragile than a transplant making them much easier to handle.
They are less prone to disease and bolting, especially if you are planting them over Winter.
They are much faster to plant, especially if you are growing many of them!
They always yield larger onions for us compared to onion seeds.

hand showing how big an onion is in the garden.

What are Onion Sets?

Onion sets are small dry immature bulbs of onions that are grown from seed, dried and then then packaged for you to grow the following season. Many people (including me) find them easier to work with than onion seeds.

They usually come in a mesh bag or a box depending on where you buy them from.

When to Plant Onion Sets

Onion sets are planted about 4-6 weeks prior to freezing temperatures. This gives the bulb some time to sprout before a long winter dormancy. In NYC, hardiness zone 7b, we plant our onion sets in mid to late October.

Bonus: Looking for more Fall/Winter gardening tips? Make sure to plant cover crops in your garden too!

Where to Plant Onion Sets

Onions like to grow in a well-drained garden bed that has been enriched with composted organic matter and gets full sun. We take lots of pride in making our soil the best for our plants! Make sure to check out how we use cover crops in the Fall to better our garden soil too.

Make sure you are practicing good crop rotation to help prevent disease and pests by not planting onions in the same spot every year or where you’ve planted onions or leeks recently.

How To Plant Onion Sets

Dig shallow rows for the onions. Generally onion sets are planted 1-2 inches deep.

Plant each bulb with the roots down and pointy side up.

Space the onions 4-6 inches apart with rows spaced 10-15 inches apart.

Cover them back up with soil and then water so the soil is moist.

Thoroughly mulch with shredded leaves or straw. The mulch will help protect the plants.

straw being added on top of garden for onion sets.

Caring for Onion Plants

Onions are an easy crop to care for if you keep them well mulched with straw or leaves. To get the biggest onions the soil should be weed free with consistent moisture. Mulching will help with both of these things and make things easier for you.

When To Harvest Onions?

Fall and Winter onions take about 260 days until harvest. Fall plantings of onions are typically harvested in late spring – early summer. If you are having a warm fall, you may see the onions sprout before winter. This is ok, just keep them well mulched.

Onions are ready for harvest after the tops have fallen over and turned brown.

We love making it a family day at the garden with our girls digging up the onions! We make lots of onion recipes with our garden grown onions, including turning some into onion powder so we can remember our garden onions year-round.