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How to Grow Onions: A Complete Guide

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Onions are pretty easy to grow. While starting onions from seed takes a little patience and know-how, once you have seedlings, they’re really simple to grow. Onions are a versatile crop and one that we really enjoy growing. Let’s discuss how to grow onions so you can add this simple crop to your garden!

Onions growing in a garden

Like garlic, we use a lot of onions here and it’s one of a handful of crops we are completely self-sufficient with, even with our small property. I love growing onions because they’re versatile, being able to be utilized at several stages, and they’re simple to grow.

Types of Onions

Short day, Intermediate day, and long day Onions

Onions are divided into three types short day, intermediate day, and long day. This distinction determines how much sunlight is required to form a bulb.

Each onion type is best suited for certain growing zones, so knowing which gardening zone you’re in will help you decide which type of onion is best suited for your particular garden. However, many people have luck with different types, such as short days in a colder zone, or long days in a warmer zone, so feel free to use a little experimenting and choose what works best for you.

Short-day onions require the least amount of sunlight to form a bulb, at around 10 hours of sunlight a day. These onions grow best in USDA hardiness zones 7 and up as these southern areas of the country have shorter daylight hours than northern gardeners.

Short-day onions can be grown further north than zone 7, but they may flower soon, resulting in smaller bulbs because the added daylight hours will trigger flowering. All said, these varieties do not store as well as intermediate or long-day onions, so keep this in mind when choosing.

Short-day onions are also said to be sweeter than long-day onions and some popular short-day onions are “white Bermuda” and “red creole”.

Intermediate day onions also referred to as neutral day onions, require about 12 to 14 hours of sunlight to form bulbs, but this particular type is pretty adaptable being able to be grown in a large portion of the United States. However, it is said that these types are best suited for zones 5 and 6 where they have sufficient hours of sunlight.

Farther north gets a bit too much light, farther south, a bit too little. That’s not to say they can’t be grown in these areas successfully, they can. They’re just best suited for zones 5 and 6.

These varieties will store better than short-day, but they’re not the best-storing onions. One variety we’ve successfully stored before is “candy”.

Long day onions will do best in the northern parts of North America from zone 6a and north. These varieties will require 14 to 16 hours of sunlight to form bulbs. That said, these varieties are the best-storing onions. When provided with sufficient sunlight, they will form large bulbs and store for long periods when stored properly.

Our favorite long-day variety to grow here in Indiana is “Stuttgarter” another very popular variety is “Walla Walla”.

Bulbing Onions, Green Onions, and Scallions

Freshly harvested scallions

Bulbing onions come in a variety of colors and types from red to sweet and everything in between, but beyond that, bulbing onions can be enjoyed as green onions or scallions dependent on when they’re harvested.

You can pick immature bulbing onions and have green onions or scallions. However, there are also varieties known as “bunching onions” that do not bulb that can be grown just for this purpose, if you choose.

How to Grow Onions

Starting Seeds

Packets of onion seed on top of a seedling tray ready to be planted.

Unless you live in a warmer climate where the ground doesn’t freeze over the winter, you’ll want to start seeds indoors.

Onion seeds will be one of the first seeds you begin indoors, about 8 to 10 weeks before your last expected frost.

Unlike some seeds, onion seeds should be started in fairly large growing pots so you don’t disturb the root systems. We use these with good success, we just punch holes in the bottom for drainage. Another good option is berry containers.

You’ll want to dampen the seed starting mix, place it in the container and then place the seeds on top. Lightly cover them with a thin layer of the seed starting mix.

Onions germinate better with a bit of humidity (leave the dome on while you await germination) and a bit of heat (a heat mat or a greenhouse is ideal for this).

Keep the soil moist, not letting it dry completely between watering, but do not overwater.

Once you begin to see germination, remove the dome and the heat mat.

Make sure you keep your seedlings in full-spectrum sunlight (a grow light will help here) for 12 hours a day, and then provide 12 hours of darkness.

Onions grow quickly once they germinate. When your seedlings are roughly 5 inches tall, cut the tops down to about 2 inches in height using a pair of sharp scissors. You can utilize these greens in dishes if you choose.

Onions are also heavy feeders. Fish emulsion can be utilized weekly after they germinate to help them have the right levels of nitrogen to thrive.

Hardening Off Onion Seedlings

Like all seedlings started indoors, you’ll want to acclimate your seedlings to the outdoors. This process is often referred to as “hardening off”.

To successfully do this, about a week or so prior to transplanting your seedlings outside, you’ll want to put them in a protected, outdoor place to acclimate to the unpredictable outdoor elements.

On the first day, leave them out for about 3 hours and then bring them back indoors, the second day 4 hours, and so on until you’ve left them out for a full day.

Transplanting (or planting) Outdoors

Preparing to plant an onion seedling in the soil

Whether you chose to utilize sets, or you grew from seed, once the threat of frost and torrential rains have dissipated (about 2 weeks after the last frost), it’s safe to transplant your onions outside.

You’ll want to leave roughly 4 to 6 inches between each plant and if planting in rows, space rows 12 to 18″ apart for the best results.

If you’re planting sets, you’ll just plant the bulb into the soil.

If you’re planting transplants, you can put 2 to 3 seedlings together, or separate them all into individual transplants. Just be careful so you don’t damage the root systems as you pull them apart.

Personally, I plant each transplant individually, but you’re still going to have great results if you plant 2 or 3 together, so the choice is really up to you.

Some folks like to trough out rows, I simply place a dowel rod into the soil to make a hole large enough and place the set or seedling in. Gently tamp down the soil around it and that’s all there is to it.

Growing and Maintenance for Onions

Water

Once everything is transplanted, water the onion beds, but don’t saturate them.

If you planted sets, you’ll water daily until the plants germinate.

If you grew from seed, just water when the soil begins to dry out, typically once or twice a week.

Mulch

Onions and weeds do not get along. Not only will mulching help retain moisture in the soil, it will also help control weeds in the onions so they’re not competing and you won’t struggle come harvest time.

Fertilize

Onions are heavy nitrogen feeders, without proper nitrogen levels, the bulbs will not form correctly.

I highly suggest you test your soil, where we are at, we have high levels of nitrogen in the soil and I’ve not actually had to fertilize my onion beds once they’re transplanted.

However, if you test your soil and it’s highly lacking in nitrogen, or your onion crop is looking a little lackluster rabbit poop is a fantastic, organic source of nitrogen that can be used straight on the garden.

If you need to fertilize, do so every few weeks until two weeks before harvest.

How long do onions take to grow?

Freshly harvested onions

Onions take about four to five months to reach maturity when grown from seed.

If you plant sets, you’ll be ready to harvest in just a couple of months.

If you’d like to harvest green onions, you can do so in about a month after transplanting.

Harvesting Onions

Onions with their tops flopped over, ready to harvest
Onions are ready to harvest when the tops begin to flop over and brown and the bulbs begin to push above the soil level.

You can harvest onions at any point once they’re established if you want to eat fresh onions or green onions.

That being said, you’ll know your onions are ready to harvest when the green tops begin to flop over and turn brown and the crowns are beginning to pop above the soil level.

To harvest, simply grip the base of the green and pull upward towards the sky. The onions should pull right up out of the soil.

If they’re stuck, you can use a little hand trough to help dig the soil out from around the bulb, just be mindful to not damage the bulb itself.

Drying and Curing Onions

Onions curing on a surface.
Onions can be dried by laying them out on a flat surface.

Once you’ve harvested your onions, they’ll need to be dried and then cured. You’ll lay them out, with the greens still attached for about a week until they form that “skin” on their exterior to dry them, first.

Many folks, as long as the weather is dry and sunny, will just lay the onions out on top of the soil to dry. We lay ours out on top of screens to dry so the air circulates all around them. We do this in a partially shaded area for one week.

Once dried, the onions still need to cure or they will not store well at all. The time this takes varies. The best indicator is if you begin to cut or remove the green they will seep a milky white substance, this means they still need curing time.

If you make a small cut and they don’t have any liquid seeping out, they’re ready to put into storage.

Since we braid our onions, we actually braid them together after they’ve dried and they receive adequate ventilation and time to cure without consequence.

Storing Onions

Braided onions hanging for storage
Storage type onions can be stored by braiding and hanging them in a cool, dry, dark space.

We prefer to keep the greens attached and braid the onions with some string. We simply braid several (about 10) together, hang them in a dark corner of our garage and pull in one braid at a time as needed to use in the house.

If you prefer, you can cut the greens off and store them in mesh bags.

Regardless of your storage method, you’ll want to keep them in a cool, dark, well-ventilated area for the best results. A garage, a cool basement, a root cellar, or the like is best.

If you don’t have the means to store them, you can cut them and freeze them. You can also pickle them and dry them for various uses later on.

Onions, when stored in proper conditions, will keep for at least 6 months. In our experience, we can keep onions in our cool, dry, dark garage up until the next harvest.

Onions are fairly easy to grow, and I love the ability to choose whatever varieties I want and test them out. Some mature faster than others so I can kind of stagger the season a bit, and they’re fun to cure and delicious to use. Just one step closer to that self-sufficient homestead! 

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Lisa Brugnano

Friday 3rd of January 2020

Nice article. How do you prevent onions from bolting? I'm in southern California and my onions usually go to seed rather than forming a nice bulb. I use short day onions. Thanks.

Danielle McCoy

Friday 3rd of January 2020

Since you're in California, I would say water is your best friend to try to prevent bolting. Make sure you mulch around your onions to keep the soil a little cooler and keep the moisture level up. And water them. The water, as it evaporates, will help cool the air around them. It's probably just getting way too hot. And if you happen to have a random cold snap, cover them up. Onions bolt due to stress typically caused by temperature fluctuations or lack of water, so keep them watered (not drenched) and that will help keep them cool. If the onion does bolt, snip off the flowers and harvest it, eat it as soon as possible as they don't store well, but they're still edible.

Julie

Friday 4th of January 2019

Danielle - growing onions is something I want to add this year, so thank you for this timely post! It does look easy, and I am less intimidated now about growing from seed. I am half way through cleaning out my greenhouse (I would have had it finished, except for all this rain!), and will be ready to start planting by February. Great information - I am going to print this out and put it in my garden book!

Danielle McCoy

Friday 4th of January 2019

Hi Julie, it is really easy! I hope the post helps you have a bountiful harvest!

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