Growing onions is a popular task for millions of gardeners and knowing when to harvest red onions – along with yellow and white varieties – is important for success. If you harvest onions too early, it means a limited storage life. But, harvesting too late could mean a split or rotten bulb. In this article, I’m going to review two perfect times for harvesting red onions. One is ideal for fresh use and the other is best for optimizing storage life.
Why knowing when to harvest red onions matters
Like their cousins chives, leeks, shallots, and garlic, red onions are a member of the onion family (Amaryllidaceae). Planting immature red onion bulbs (known as sets), seeds, or seedlings in the early spring is a rite of passage in the garden. For many, it signals the start of the growing season since onions can be planted even as the last snow of the season falls (called an “onion snow” by my Pennsylvania Dutch ancestors).
Though there are many different types of onions, for many growers, red onions are a favorite, myself included. I enjoy their tangy flavor and the color they add to dishes. In this article, I’m going to focus on when to harvest red onion varieties, though this information is appropriate for other varieties, too.
Before we get to the harvest, it’s important to share quick rundown of the planting and growing process. As mentioned, red onion plants are grown from either onion sets (second year bulbs), red onion seeds, or red onion transplants (young, first year plants). I offer extensive information about growing onions from seed and why it is beneficial in this separate article. That being said, growing red onions from sets or transplants is fine, too. I often do a combination of both.
Plant your red onions a few weeks prior to your last expected spring frost. They shrug off cold weather and cold soil like a champ. Early planting gives the bulbs plenty of time to form throughout the growing season. Working compost into the soil prior to planting and adding a layer of straw or shredded leaves as mulch cuts down on weeds and reduces watering needs.
It’s important that your plants receive at least 8 hours of sunlight and that the soil pH is between 6.0 and 7.0. Be sure to trim off the flower stalks should any appear. You want the plant’s energy to be dedicated to bulb production, not flowers.
Which type of red onion to plant
Before planting, it’s important to select the right varieties of red onions for your climate. Onion bulbs begin to form when the hours of daylight reach a certain threshold. Some varieties of red onions have a very low threshold. These are known as short day onions, and they are best for southern climates between latitudes of 25° and 35°. Short day red onions begin bulbing-up when day length reaches just 10-12 hours. If you grow short-day red onions in Northern climates, they won’t form good sized bulbs. Short-day red onions include Desert Sunrise, Red Rock, and Giant Red Hamburger.
Long day onions are best for northern latitudes. They begin to form bulbs when day length reaches 14-16 hours. Long-day varieties are often grown for long storage. Latitudes above 37° are best. If you grow long day onions in the south, they won’t form good sized bulbs. These are what I grow in my Zone 5-6 garden here in Pennsylvania. Red long-day choices include Barolo, Rossa di Milano, Redwing, Southport Red Globe, and Red Carpet.
Then there are day-neutral varieties of red onions. Also known as intermediate-day onions, these varieties grow best across the mid-section of the U.S., between the latitudes of 32° and 42°. The day length they require for bulb set is 12-14 hours. Red onion varieties in the intermediate-day category include Monastrell and Red Candy Apple.
When to harvest red onions for use as scallions
Now that you’ve planted and grown your onions, let’s get to the harvest! As mentioned earlier, there are two ideal times to harvest red onions. The first is as a young, immature onion, known as a scallion that’s eaten fresh. The second is as a mature bulb. Scallions are best for immediate use while mature bulbs are great for storage. The flavor of scallions is more mild than mature onion bulbs, and you eat the green leaves in addition to the immature bulb.
Scallions can be harvested in as few as 30 days from planting onion seeds, or when the plants are about 8 to 10 inches tall. The young onion seedlings known as scallions are best grown from seed, but you can harvest scallions that are grown from transplants, too. Here is an extensive article on how to grow scallions from white or red onion types if you want more great info on how to do this.
Harvesting mature red onions for long-term storage
The more important consideration when it comes to knowing when to harvest red onions is if you plan to use them as storage onions for later consumption. This is when timing is critical. Harvest red onions when the time is right, and they will last for months.
Here are some tips for knowing when to harvest red onions for storage.
- Harvesting mature red onions can take place anytime from early July through late August for plants grown from sets or transplants.
- Harvests will be slightly later, perhaps as late as early October, for red onions grown from seed.
- More important than the calendar is the appearance of the plants. Red onions are ready for harvest when a third of the leaves have turned yellow and the “neck” of the plant has flopped over and the stems and leaves are laying on the ground (see photo).
- Stop watering your onions 3 to 7 days before harvest. If they were grown in well-draining soil, this means the skins will be drier and less prone to rot.
- Pull your red onions out of the ground by gripping the stem and giving them a slight tug.
- Do not wash harvested onions and do not cut off the leaves or the roots as this can promote rot.
- You’ll need to go through the process of curing to toughen up the red onion skins and prepare the bulbs for store. The next section covers how to cure red onions.
How to cure red onions
Now that your red onions have been pulled, it’s time to cure them. Properly cured red onions can be kept at room temperature. Soon after harvest:
- Brush off any excess soil gently with your hands.
- Place the bulbs in a dry place with good ventilation.
- Spread the bulbs out in a single layer. You can lay them out on newspaper, plastic crates, or drying screens. I use an old, upturned wire freezer drawer.
- The skins will dry and toughen over the next 2 to 3 weeks and the tops will shrivel.
- Do not allow the bulbs to be exposed to moisture and turn them once or twice while they are curing.
The best storage conditions for red onions
After your red onions have cured and their outer layers are dry and papery, it’s time to store them. Use a scissors to remove any dried foliage, leaving a small stump intact. Choose a storage site with good air circulation and store your onions in mesh bags, plastic or wooden crates, or even a cardboard box with holes poked in it for ventilation.
How long do red onions last?
If kept out of direct sunlight, cured red onions store for many months. The best temperature is between 45° and 55°F, though up to 70°F will suffice if you don’t have a basement or root cellar. Onion varieties bred for long-term storage will last longer than other types. Growing healthy plants, timing your red onion harvest properly, and protecting the harvested bulbs from pests like mice and rats, allows you to enjoy a pungent homegrown harvest all winter long.
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