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Everything You Need to Know About When to Harvest Red Onions

If you’re growing a vegetable garden to integrate nutritious, homegrown produce into your daily diet, red onions are a must!

When to Harvest Red Onions

This popular onion variety is an essential ingredient in many culinary creations. It is easy to cultivate, harvest, and cook; you can use it for just about any dish for breakfast, lunch, or dinner.

But how and when should you harvest your red onions for the best results?

You can grow red onions in your backyard, so you never have to buy them again. The process is fairly straightforward; you only need a few simple tools and knowledge about growing, protecting, harvesting, and storing them for long periods.

This guide has everything you need to know about when to harvest red onions from your backyard garden and how you should cure and store them.

Let’s get to it!

Quick Tips for Growing Red Onions

When and How to Plant Red Onions

You can grow red onion plants (Allium cepa) using onion sets, bulb onion, or even onion seeds. Growing red onions from sets or bulbs is much quicker—they mature within three to four months. In contrast, red onions from seeds mature within two years.

Red onion bulbs

One of the best things about cultivating your vegetable garden is that if you’re wondering when to harvest red onions, the answer spans most of the year. You can plant onions during the spring, summer, or winter, as long as you live in an area with mild weather.

We suggest planting onions in spring so you can harvest onions by late summer before the cold weather rolls in.

There are quite a few red onion varieties to choose from as well. These include:

When you’ve chosen your preferred type of red onion, you must choose the perfect spot to plant them. We suggest dedicating an area that receives six to eight hours of sunlight each day.

Next, prepare the garden bed by adding a one- or two-inch layer of compost on top of four or six inches of the soil surface.

Caring for Red Onions

Follow these tips to make sure your red onion plants grow well:

  • Regularly pull out competing weeds.
  • Give the plants at least one inch of water each week to get large, beautiful bulbs when it comes time to harvest your red onions.
  • Water the onions when the top three to six inches of soil is completely dry.
  • Spread a single layer of mulch over your red onions to keep the soil moist.

Pest and Diseases to Watch Out For

The real challenge of growing onion varieties is the pest insects.

To ensure your onions won’t get taken over by pests and diseases, make sure to keep an eye for the following:

  • Downy mildew
  • Leafminers
  • Pink root
  • Mites
  • Purple blotch
  • Onion maggots
  • Onion neck rot
  • Thrips
  • Aphids

If you notice evidence of these kinds of problems, consider adding a predator species to your garden to eat the pests, or planting your garden in a new area next year to avoid contaminated soil in the instance of fungal problems.

When to Harvest Red Onions

The right time to harvest red onions is before colder weather hits. This is because onions are not frost-tolerant. When the cold weather hits and frost forms on your plants, they will cause your perfectly mature onions to spoil.

Harvesting red onions

The exact period when to harvest red onions depends on when you planted them. Late August to early October is the general time frame according to the planting calendar.

What’s fascinating about red onions is that you can harvest them after a few weeks of planting and use the green shoots as scallions. Wait a bit longer if you want to harvest fully mature onion bulbs.

How to Tell if Your Onions Are Ready for Harvest

You will know when to harvest red onions largely by sight. Watch out for large bulbs and green tops that turn yellow and begin to fall over. The necks will become lighter in color and bend flat.

Some onions can develop small full-sized bulbs, depending on the outdoor conditions they grow in. The right conditions will result in mature bulbs that are two to three and three-quarter inches in diameter.

Keep an eye out for flower growth as they only begin to emerge when the onion bulb stops growing. When flowers start to appear, you must harvest and consume them within three days.

How to Harvest Red Onions

Continue to care for and water your onion crop until about 10% of the green tops turn yellow and fall over. You can leave some of them for an additional five to 10 days so they can continue to mature, but by and large, this is exactly when to harvest red onions.

Here’s what you need to do:

  • Use a spade tool to loosen the soil around the onion row you want to harvest.
  • Cut the onion roots carefully using the spade.
  • Lift the bulb growth from the soil—make sure the tops are intact. Hold the onions by the neck at the base of the leaves when uprooting them.
  • If the onion bulb resists when you’re pulling it, loosen the soil a little more.
  • Shake off any soil from the onions and the tops.

Once you’ve carefully pulled out your red onions, prepare to cure and store some of them so you can enjoy tasty, crunchy onions over the next few weeks and months.

Harvested red onions

If you choose to leave onions in the soil and just pick fresh onions for your next meal, follow the same steps carefully and skip the curing.

As you decide when to harvest red onions, try not to cut or bruise the bulb. This increases the chances of onions rotting, which is just a waste of resources.

How to Cure Red Onions?

While you can consume them after harvesting, you may not be able to eat or cook all of your bulbs at once. If you want to keep them for the following days or weeks, you must cure them.

Here’s a simple step-by-step process to cure storage onions:

  • Choose an airy and dry location away from direct sunlight.
  • Lay out or hang the onions with the tops intact to dry them. Keep the area well-ventilated.
  • Let the onions dry like this for seven to 10 days.

When done correctly, this simple drying process should result in the necks drying out and the shallow roots shriveling up. The bulb growth will also develop papery skins.

Drying red onions

Once the onions are cured, you can remove the dried tops and roots with pruning shears or braid them for neat storage. Leave at least an inch of foliage on the bulb to prevent rotting.

After curing, you can carefully place the red onions in a nylon stocking or mesh bag. This prevents mold and bruising.

How to Store Red Onions after Harvesting?

In a Cool, Dry Place

When you know when to harvest red onions and cure them, you can keep them in storage in a cooler spot that’s dry, ventilated, and out of direct sunlight. The storage space should maintain temperatures between 30 and 50 degrees Fahrenheit.

Locations with ideal indoor conditions to store onions throughout the year are the pantry or cellar. To ensure proper ventilation and prevent mold, place the onions inside bamboo steamers, open baskets, mesh bags, netted bags, or even pantyhose.

In the Fridge

If you have peeled, sliced, or diced onions, you can store them in the refrigerator.

Put peeled onions in an airtight container and onion slices in a resealable bag or plastic wrap.

Peeled onions will last up to two weeks in the fridge, while sliced or diced ones will last for seven to 10 days. Note the expiry date on the containers or wrap and consume the onions as quickly as possible so they will not go to waste.

If you’re interested in learning more about food storage, browse our guide to long-term food storage tips and tricks.


Should you wash red onions after harvesting?


After you learn when to harvest red onions, they must not come in contact with water. Moisture or water exposure can lead to rot.

Since onions are safe from pesticide exposure, they are safe for consumption after simple dusting. Only wash the onions that you will consume immediately.

Slicing red onions

How long do red onions last after harvesting?

After harvesting red onions and curing them, they have a shelf life of 10 to 12 months. Keep them in a dark and cooler spot at 35 to 40 degrees Fahrenheit.

Uncured onions can last several days after harvesting. In contrast, onions that have sprouted flowers must be consumed immediately.

How long does it take for red onions to grow?

It depends on how you plant them.

Onions are biennial, so growing them from plant seeds takes at least two years. In the first year, the onion seedlings grow into small bulbing onions and leaves. In the following year, the immature onion bulbs become fully-grown mature onions.

When to harvest red onions? When grown from onion sets or bulbs, they mature within three to four months. Scallions are ready for harvest when the green tops are 10 to 12 inches tall, and the onion stalks are between a quarter and half an inch wide.

What happens if you don’t harvest red onions?

Leaving onions in the soil after they’ve fully matured makes them prone to rot and damage from organisms. Onions that have completed their life cycle may even start growing again.

You will know when to harvest red onions by sight: large bulbs and yellowing tops that are bent over.

Wrapping Up When to Harvest Red Onions

This is all you need to know about how to cultivate homegrown onions. Remember, following the proper steps when to harvest red onions simplifies the process, and you can enjoy fresh onions for a long time.

Do you want to learn more about survival and wilderness food management? Browse Survival World for more survival food ideas and advice.