蜜桃恋人

How to Grow Onions: The Complete Guide

Many ripe onion bulbs as background, closeup. yellow onions
Photo Credit
New Africa/Shutterstock
Botanical Name
Allium cepa
Plant Type
Vegetable
Sun Exposure
Full Sun
Soil pH
Neutral

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Planting, Growing, and Harvesting Onions

Catherine Boeckmann

Onions are a must-grow vegetable! You can grow a substantial harvest in a small area, store your bounty for many months, and enjoy onions鈥 many culinary uses. However, some tricks of the trade make the difference between a great crop and a disappointing one. See how to plant, grow, and harvest onions.

Should I Grow Onions from Seeds or Sets?

We prefer planting onion sets over starting them from seeds simply because they will establish quickly and are easier to plant.

  • Onion sets are tiny onions that mature in about 14 weeks. They can withstand light freezes and have a higher success rate than direct-sown seeds or transplants. The onion sets look like small bulbs and are sold at gardening stores; they develop into full-size bulbs once they mature. Choose onion sets with bulbs 3/4 of an inch in diameter; larger ones tend to produce stiff necks and go to seed.
  • Of course, starting onions from seed is certainly doable and may even be necessary in colder regions (Zone 5 and colder). Onions grown from seed require the soil to be at least 50掳F to germinate, so these should be started indoors about 6 weeks before transplanting to the garden. If you’d prefer to try this method, check out our tips for growing onions from seed.

Practice crop rotation with onions. Don’t plant them in the same location year after year, as this can encourage the spread of diseases that affect the crop. Learn more about crop rotation.

Read Next

Planting

Select a location with full sun, where other plants won鈥檛 shade your onions. The more energy they can get from the sunlight, the larger their bulbs can grow. Mix aged manure or compost into the soil in the fall or early spring to improve texture. Ensure there are no rocks or debris. Soil needs to be well-draining and loose; compacted soil affects bulb development.

When to Plant Onions

  • In spring, plant onion sets outdoors as soon as the ground can be worked, usually in late March or April, when temperatures are no longer likely to dip below 28掳F (-2掳C).
  • In spring, start onion seeds indoors for about 6 weeks before transplanting to the ground (once the soil is at least 50掳贵).
  • A fall-planted crop of onions needs at least 4 to 6 weeks of warm temperatures to become established in the ground. They will remain dormant during the cool season; as the temperatures and soil warm again in early spring, the onions come back to life.
onions growing in the ground
Photo credit: YuriyS/GettyImages

How to Plant Onions

Onion plants are heavy feeders and require constant nourishment to produce big bulbs. At planting time, add nitrogen fertilizer. Many organic gardeners will add an inch of compost to the bottom of each row before planting. Or, dig a trench in the soil about 2 inches deep and 3 inches wide, and then fill the trench back in with about an inch of compost.

  • Bury onion sets 2 to 6 inches apart, gently pressing them 1 to 2 inches deep into loose soil. (Use the closer spacing if you want to pull immature onions as scallions.)
  • Space transplants 4 to 5 inches apart and rows 12 to 18 inches apart.
  • Set the bulbs with the point end up. Again, don鈥檛 bury them more than 2 inches under the soil. It鈥檚 critical that onions aren鈥檛 planted too deep, as this can affect bulb development.
  • Mulch with straw between rows to help retain moisture and stifle weeds.

Spacing for Onions

Growing

We find it helpful to think of onions as a leaf crop (like lettuce or kale) rather than a root crop (like beets or carrots). Fostering healthy foliage growth ensures the plants have enough energy to form large bulbs.

  • Ensure immature bulbs stay covered with light mulch to protect them, retain moisture, suppress weeds, and allow air circulation.
  • Do not cover emerging onions.
  • Fertilize every few weeks with nitrogen to get big bulbs. Stop fertilizing when the onions push the soil away, and the bulbing process has started. Do not put the soil back around the onions; the bulb needs to emerge above the soil.
  • Generally, onion plants do not need consistent watering if light mulch is used. About 1 inch of water per square foot per week, including rainwater, is sufficient. If you want sweeter onions, water more. To deter bolting, water them often during hot spells. 
  • To deter thrips, intercrop onions with tomatoes or carrots in closely alternating rows.

See our video demo to see how to plant and grow perfect onions! 

 

Growing Onions in Containers

You can also grow onions in containers! Prepare a container that is at least 10 inches deep and as wide as possible (to allow for space between maturing onions). A 5-gallon bucket will support 4 to 6 onions, and a tub many more. Place the container where it will receive the maximum hours of direct sunlight per day. (It will be heavy to move once filled and planted.) 

Provide a well-draining potting mix that is rich in organic matter; add compost or well-rotted manure. Mix in a complete fertilizer, per the package guidance on container size, or fertilize with or compost tea.

Types

鈥 meaning they grow in response to day length鈥攖he number of daylight hours needed to trigger bulb formation. Short-day onions grow best in the southern United States, between 25掳 and 35掳 north latitude, and start bulbs when day length reaches 10 to 12 hours. The earlier that short-day onions are planted, the larger they get. In the South, onions can be planted in the fall and overwintered. Since they continue to grow throughout the winter, they will be ready for harvest in the spring.  

Intermediate, or day-neutral, onions are best suited to the middle tier of U.S. states, approximately between latitudes 32掳 and 42掳, and start bulbs when day length reaches 12 to 14 hours. 

Long-day onions grow best in the northern states, between latitudes 37掳 and 47掳, and start bulbs when day length reaches 14 to 16 hours. 

Do not try to fool Mother Nature: Short-day onions planted in a long-day zone will result in small bulbs鈥攏ot an early harvest. 

Long-day varieties:

  • 鈥榊ellow Sweet Spanish’: large, round shape; yellow-white.
  • 鈥楩irst Edition’: high-yielding, stores well, flavorful, creamy-yellow
  • 鈥楻ed Wethersfield’: flat bulbs that store well, white flesh, red-skinned
  • 鈥楢isa Craig,鈥 鈥榃alla Walla’: huge bulbs
  • 鈥楤耻蹿蹿补濒辞,鈥 鈥楴辞谤蝉迟补谤’: produce early but keep only until late December
  • 鈥楥辞辫谤补,鈥 鈥楽outhport Red Globe,鈥 鈥楽weet Sandwich,鈥 鈥榊ellow Globe’: keep well
  • 鈥楻ed Florence’: heirloom; 4- to 6-inch long, dark purple-red, torpedo shape; mild, sweet
  • 鈥楢ilsa Craig鈥: heirloom; named for a Scottish island; large, up to 8 inches in diameter; average 2 pounds; pale yellow skin, globe shape; mild, sweet 
  • 鈥楪old Coin鈥: cipollini; 1 1/2- to 3-inch yellow flattened bulb; pungent flavor sweetens when cooked

Short-day varieties:

  • 鈥楽迟耻迟迟驳补谤迟别谤鈥: sold in sets, early maturity with a slightly flat shape, yellow
  • 鈥榃hite Bermuda’: extremely mild, with thick, flat bulbs; white
  • 鈥楻ed Burgundy’: good table onion with mild, sweet white inside; short-term keeper
  • 鈥楥rystal Wax White Bermuda’: a great onion for pickling when harvested at 鈥減earl鈥 size
  • 鈥楬ybrid Yellow Granex’: sweet, Vidalia type
  • 鈥楻ed Creole鈥: heirloom; 3- to 4-inch, dark red globe shape; pungent
  • 鈥楽outhern Belle’: ruby color throughout
  • 鈥楾exas 1015-Y Supersweet’: stores well
  • 鈥Yellow Granex鈥: Vidalia type; 3- to 4-inch, yellow, flattened globe shape; crisp; said to be the sweetest of the super sweet

Day-neutral or intermediate  varieties:

  • 鈥楥补苍诲测’: golden, thick-flesh, jumbo bulbs; stores well
  • 鈥楻ed Stockton’: large, red-ringed, white-flesh bulbs
  • 鈥楽uper Star’: large, sweet, white bulbs
  • 鈥楶耻谤辫濒别迟迟别鈥: mini onion, at 1 1/2 inches; glossy, burgundy red when raw; pastel pink when cooked or pickled; mild, sweet
  • 鈥楽outhport Yellow Globe鈥: early; 2 1/2- to 3 1/2-inch thick-skin yellow globe; mild, sweet

Harvesting

Pull any onions that send up flower stalks. This means that the bulbs have stopped growing. These onions will not store well but can be used in recipes within a few days.

  • Spring-planted onions tend to be ready for harvesting by mid-summer. 
  • When onions start to mature, the tops (foliage) become yellow and begin to fall over. At that point, bend the tops down or even stomp on the foliage to speed up the final ripening process.
  • Loosen the soil around the bulbs to encourage drying.
  • Harvest by late summer in dry weather. (Wet-harvested onions do not cure well and might rot in storage.)
  • When the tops are brown, pull the onions. Handle them carefully, as the slightest bruise (now and in storage) will encourage rot. 
  • Cut the roots and trim the tops back to 1 or 2 inches (but leave the tops on if you are planning to braid the onions together).
Harvested onions still covered in dirt in the garden . Photo by Rootstocks/Getty Images
Photo by Rootstocks/Getty Images

How to Store Onions

  • Set onions on dry ground for a few days to cure, weather permitting, or in a protected place such as a garage or barn. 
  • Once cured, hang onions in a mesh bag or nylon stocking; spread up to two layers deep in a box; or braid and hang them in a cool, dry, well-ventilated area. The ideal temperature range for storage is 40 to 60掳F (4 to 15掳C). Do not store in a refrigerator, as conditions will be too damp.
  • Check periodically for sprouting or rotting onions and remove them.
  • Don鈥檛 store onions with apples or pears, as the ethylene gas produced by the fruits will interrupt the onions鈥 dormancy. Onions may also spoil the flavor of these fruits (as well as potatoes).
  • A pungent onion will store longer than a sweet onion. Sweet onions have a high water content and do not keep well. Eat the sweet varieties first and save the more pungent onions for later.
  • To avoid bruising, store them so that they do not touch each other鈥 for example, in clean old pantyhose. Slip in the onions one at a time, tying a knot between each one. Hang them in a cool, dry place.
  • You can also braid your onions for extended storage. Learn to braid onions!

Check out this video to learn how to harvest and store onions.

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Wit and Wisdom

Onions were worshiped in ancient Egypt, where their concentric circles were seen as symbols of eternal life.

Can You Plant a Sprouted Onion? 

Yes, you can plant a sprouted onion, though you won’t get more onions from it. You will get lots of tasty green sprouts, however! Here’s how to do it:

  1. Fill a pot with potting soil and make a hole in the middle about the onion’s depth and width.
  2. Place the onion in the hole and cover with soil.
  3. Water and put the pot in a sunny spot.
  4. Harvest the green sprouts as needed for cooking.

If you get a sprout with a flower, wait until the flower goes to seed. Save the seeds for planting in the spring.

Onion Cures and Home Remedies

  • In the Middle Ages, onion juice was believed to cure baldness, snakebite, and headaches.
  • A generation or two ago, children were treated with a poultice of mashed onions applied as a paste to cover a wound.
  • A whole onion eaten at bedtime was prescribed to break a cold by morning, and sliced onions were placed on the soles of the feet to draw out fever.
  • Early settlers made cough syrup by steeping raw onion slices in honey overnight.
  • A raw onion rubbed on a bee sting or insect bite will relieve the pain and itching.

Onion 蜜桃恋人 Folklore

Onion’s skin very thin,
Mild winter coming in;
Onion’s skin thick and tough,
Coming winter cold and rough.

Pests/Diseases

  • Thrips: To control thrips鈥攖iny insects about as fat as a sewing needle鈥攖ake a dark piece of paper into the garden and knock the onion tops against it; if thrips are present, you will spot their tan-colored bodies on the paper. A couple of treatments with insecticidal soap kills them. Follow the package directions. Spray the plants twice, three days apart, and the thrips should disappear. To prevent future infestations, consider using row covers.
  • Onion Maggots: Cover your emerging onion crop with fine mesh netting or row covers. Seal it by mounding the soil around the edges. The onion maggot fly likes to lay its eggs at the base of plants, so the netting should prevent that. You should also keep mulch away because the insects like decaying organic matter, and make sure you completely harvest your onions as the season progresses. Onion maggots are usually a problem in very rainy periods, so these precautions may be unnecessary if you have a dry season.
  • White Rot: This very serious disease starts with infected plant material. Avoid transplants grown in soil-based compost. Stick to starting from onion seeds, onion sets, and bulbs bought from inspected producers. With white rot, the foliage will yellow and wilt; below ground, white, fluffy fungal growth appears on the base of the bulb. Unfortunately, once rot sets in, there is no solution. Dig up the crop and dispose of it in the trash (do not compost). Avoid growing onions in the same location in future seasons, as the dirt will remain infected for many years.

Recipes

Vermont Farm Sandwich
Egg, Cheese, and Caramelized Onion Tortillas
Grilled French Onion
Fresh Onion Dip
Potato Pizza With Sweet Onions and Rosemary
Slow Cooker French Onion Soup

Cooking Notes

To make onions taste milder, soak them in milk or pour boiling water over the slices and let them stand for 20 minutes. Rinse with cold water.

Chopping onions can sometimes look daunting: There’s the skin and the layers… Where to begin? Check out our tips for chopping onions in four easy steps. Onion skins actually have several health benefits, too, so don’t throw them out!

Check out more tips on using onions in the kitchen and cooking them correctly.

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About The Author

Catherine Boeckmann

Catherine Boeckmann loves nature, stargazing, and gardening so it鈥檚 not surprising that she and The Old Farmer鈥檚 蜜桃恋人 found each other. She leads digital content for the 蜜桃恋人 website, and is also a certified master gardener in the state of Indiana. Read More from Catherine Boeckmann
 

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Comments

neumani munuo (not verified)

8 years 1 month ago

I like the information how do I test pH and nitrogen content at the farm.

jim (not verified)

7 years 8 months ago

Contact your local Agriculture Extension Office for a soil test kit. The results will provide a wide spectrum of information and advice on steps to take to change the soil to improve it.

Eugene Dodge (not verified)

8 years 4 months ago

Would like to keep up on ideas !

Dick (not verified)

8 years 4 months ago

Our onions have beautiful tops but the size of the bulb is about the same as when we planted them. I read here that depth of planting appears to be critical and we may have planted too deep but we followed instructions on the package - we used onion sets, red and yellow. It appears we may need more nitrogen but are there any other options for us with fall coming in the not too distant future to increase the size of the onion bulb. We're in region 5. Suggestions would be appreciated. In advance, thanks for your assistance.

Dwight James (not verified)

7 years 9 months ago

I think your Bulb Size problem is you're using onion sets... Use the onion plants if you want large storage onions like you buy at the grocery store... I've been growing a garden for almost 50 years... We only use onion sets for green onions They never get large bulbs only about 1-inch bulbs... We always use onion plants you can buy at your local garden centers in a bunch with about 60 plants per bunch... There is a good site online called Dixondale Farms with all the plants and growing info you would need to know to grow nice large onions... Google it...

Glad you asked, Dick! I had the same outcome when I pulled a couple of reds recently. There are several factors involved and most have to do with soil. pH is critical; it should be between 6.0 and 7.0 (even 6.8). And it should have a couple of inches of composted organic matter in it. A good slow-release fertilizer helps, too. Or you could fertilize ever couple of weeks or so. Good drainage is essential…and so is consistently regular watering. And weeding. You could be right about nitrogen; do a soil test. And consider that onions are light/sun-sensitive. You need to know that they are suited to your latitude (day length).

Does any of this sound like something/s you could have done differently?? (It does to me!)

Laura (not verified)

8 years 4 months ago

Your info on growing onions was great and to the point.

Gerrit (not verified)

8 years 5 months ago

If the onions are breaking ground and the stalks are still real green should I cover the exposed onion with more dirt.

The area at the base of the stem, where it meets the bulb, is indeed vulnerable. If the bulbs are still small and far from ready to harvest, you might want to cover them with a light mulch that will simultaneously protect it, keep moisture in, suppress weeds, and allow air circulation. 

Dihann Lehman (not verified)

8 years 5 months ago

My onions are flowering is this ok