The Complete Guide to Properly Storing Onion Sets

I’ve had several readers write to me lately asking me if transplants would be alright shipped across country. They also wanted to know how long the onions would keep.

Onion sets are miniature onion bulbs that can be planted to grow into full-size onions They are convenient for gardeners who want to skip the seed starting stage and get a head start on their onion crop Onion sets are typically only 1/2 to 1 inch in diameter, making them fast and easy to plant.

But what if you buy or harvest your onion sets well before your ideal planting time? Knowing how to properly store onion sets is crucial to keep them healthy and viable until you are ready to put them in the ground. Follow this complete guide to get the best storage results.

Why Good Storage Matters

Onion sets are live bulbs not seeds. If you don’t store them correctly, they can start sprouting early or even rot away completely. You want firm, dormant bulbs that will vigorously grow when planted. Proper storage conditions prevent premature sprouting and rotting. It also protects the bulbs from diseases that could kill them or weaken their growth. Taking the time to store sets right will pay off later with a bountiful onion harvest.

Ideal Storage Conditions

To keep onion sets in top shape, you need to provide conditions that mimic their natural overwintering process. This means cool temperatures, low humidity, and good air circulation. Here are the optimal storage parameters to aim for:

  • Temperature 35-50°F

  • Humidity: Below 70%

  • Airflow: High circulation

  • Light: Complete darkness

  • Duration: Up to 8 months maximum

Let’s look at how to achieve each factor when storing sets at home.

Storing Onion Sets Step-By-Step

Follow these steps to successfully store onion sets for planting:

1. Cure Harvested Sets

If you have grown and harvested your own sets, they need 2-3 weeks of curing before storage. Leave them scattered in a single layer in a warm, dry, airy spot out of direct sunlight. The onion skins will further ripen and seal up during this period.

2. Choose the Right Container

Onions and onion sets love ventilation to keep them cool and dry, so you don’t want to put them in a solid or sealed container such as a box or jar. Instead, opt for mesh shelves or net bags that hold your onions while exposing them to the air flow of the room.

3. Place in a Cold Location

Find an area of your home that maintains temperatures between 35-50°F, such as an unheated basement or garage. The refrigerator is too cold and humid. You can also use an uninsulated shed or porch during winter months.

4. Ensure Good Air Circulation

Stagnant air will lead to mold and rot. Point a small fan directly on the onions to keep air moving around them. Make sure no sets are crowded together blocking airflow. Stir or shake the container periodically as well.

5. Keep Them Dark

Light causes onion sets to sprout early. Cover containers with a dark bag or cloth, or store in a dark closet or cabinet. Avoid peeking!

6. Check Often For Issues

Look through the sets every 2-4 weeks and remove any that are moldy, damaged, or sprouting. Just a few bad onions can accelerate spoilage.

Storing Sets Short-Term vs. Long-Term

The maximum storage time for onion sets is around 8 months. However, the longer you store them, the more likely some will deteriorate or sprout early despite your best efforts. Here are some storage tips for different time spans:

  • Less than 2 months: A basket or crate in a cool basement may suffice
  • 2-4 months: Use mesh bags in a cold garage or shed
  • 4-8 months: Best to use mesh shelves in an unheated space like an enclosed porch

If keeping sets more than 2 months, check them very frequently – at least every 2 weeks. You’ll likely see some sprouting and will need to remove those bulbs promptly.

Troubleshooting Common Onion Set Storage Problems

Even with ideal conditions, you may still encounter some issues during storage:

  • Mold – Caused by excess moisture. Discard moldy sets immediately and improve airflow.

  • Rotting – Also from too much humidity. Throw out rotten bulbs and store in a drier spot.

  • Sprouting – Due to warm temperatures or light exposure. Remove sprouted onions ASAP before it spreads.

  • Shriveling – Results from insufficient humidity. Lightly mist sets with water to add a little moisture back.

With diligent monitoring and quick intervention, you can keep problems to a minimum and store your sets successfully.

Storing Leftover Sets from Planting

Got leftover onion sets even after planting all you need for the season? Here are some options for storing the extras:

  • Plant them very close together in a small patch to grow green onions or bunching onions for salads and cooking. They don’t need as much room to swell.

  • Give them to gardening friends or family members who want to skip seed starting.

  • Save in ideal conditions for fall planting or next year’s garden.

  • Interplant them densely between slower growing vegetables that have empty space, like Brussels sprouts or cabbage.

Don’t just leave extra sets to rot in a bag or bucket! With proper care, they’ll stay fresh for planting or eating.

Enjoy an Easy Onion Crop with Proper Set Storage

Storing onion sets correctly takes some work, but it is worth it. You’ll have perfectly sprouted bulbs ready to go into the ground on your desired planting date. And you can feel good knowing you didn’t waste purchased or homegrown sets due to spoilage. Just be sure to provide cool temperatures, lots of air circulation, and darkness. With attentive storage habits, your sets will thrive until it’s time to turn them into a bountiful onion harvest.

They Must Have Air

It’s very important that you not leave them packaged or bundled. They’ll rot if you do.

Make sure to spread them out so they can get air. They’ll be fine until you plant them.

They Know How to Ship

Companies that ship onions all the time know how to do it so that your onions get to you in perfect condition. There is a very small chance that your transplants will be in great shape when they get to your house.

To keep them as good as new until you can plant them here’s what you do:

The minute they arrive at your door

  • remove them from the box;
  • take the rubber bands off the bunches;
  • spread them out so the air can get to them. (I like to spread them out in shallow boxes. ).

Keep them out of direct sunlight. I used to keep mine in the garage, but now I like to keep them in my mud room/enclosed porch where I can keep a fan running all the time if it gets too hot in the porch.

How to Store Onion Sets


What’s the best way to store onion sets?

Hang the mesh bag in a cool, dry place with good air circulation. Basements aren’t ideal locations, as they tend to be damp, which can cause rot when storing onion sets. Instead, consider using a semi-heated or connected garage, an attic, or even an uninsulated closet.

How long do onion sets last before planting?

IF YOU PURCHASED ONION PLANTS… Keep cool and dry until you can plant. Plants may appear dry, don’t be alarmed; they’re simply dormant. Don’t worry if you can’t plant them immediately, even if the roots and tips begin to dry out. The onions can live off the bulb for approximately three weeks.

How do you store onion sets?

Storing onion sets is much like storing plain old onions. Find a mesh type bag (like the bag your store-bought cooking onions come in) and place the onion sets inside the bag. Hang the mesh bag in a cool, dry place with good air circulation. Basements aren’t ideal locations, as they tend to be damp, which can cause rot when storing onion sets.

What temperature should onion sets be stored?

The ideal temperature for storing onions sets is between 32 and 40 degrees Fahrenheit. Keeping the sets at this temperature range will ensure that the sets do not sprout prematurely or rot. In addition to cool temperatures, onion sets should be stored in a dry environment. Onion sets are very prone to rot as they are quite high in moisture.

How long do onion sets last?

Just make sure that the container has holes in the bottom to allow for air circulation. Onion sets can be stored for up to six months in a cool, dry place. However, it is best to plant them as soon as possible after harvesting to ensure that they produce a good crop of onions. Onion sets are a great way to get a head start on your spring garden.

How do you keep onion sets from rotting?

Place the onion sets in a single layer in a cardboard box or other container. Make sure there is good air circulation around the sets. Fill the container with dry sand or sawdust, leaving about 1 inch of space at the top. The sand or sawdust will help to absorb moisture and prevent the sets from rotting. Store the container in a cool, dry place.

Leave a Comment