Growing Onions

Planting, Growing, and Harvesting Onions

Onions
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Onions are a cold-season crop, easy to grow because of their hardiness. Here’s how to grow an endless supply of onions in your garden!

Typically, onions are planted early in the spring and harvested in the fall after their tops begin to die back. In the southern U.S., some onion varieties can be planting in the fall.

We recommend using onion sets, which can be planted without worry of frost damage and have a higher success rate than direct seed or transplants.

Onion plants grow well on raised beds or raised rows at least 4 inches high. If you’d prefer to start your onions from seeds, check out our tips for growing onions from seed indoors.

Planting

How to Plant Onions

  • Plant onions as soon as the ground can be worked in the spring, usually late March or April. Make sure outdoor temperatures don’t dip below 20°F (-6°C).
  • Select a location with full sun, where your onions won’t be shaded by other plants.
  • Soil needs to be well-drained, loose, and rich in nitrogen; compact soil affects bulb development.
  • Add aged manure or compost to the soil in early spring, before planting. Onion plants are heavy feeders and need constant nourishment to produce big bulbs.
  • At planting time, mix in some nitrogen fertilizer.
  • Onion seeds are short-lived. If planting seeds indoors, start with fresh seeds each year. Start seeds indoors about 6 weeks before transplanting to the garden.
  • Think of onions as a leaf crop, not a root crop. When planting onion sets, don’t bury them more than 1 inch under the soil.
  • For sets or transplants, space plants 4 to 5 inches apart in rows 12 to 18 inches apart.
  • Practice crop rotation with onions.
  • Add mulch between the rows of onions. This will help retain moisture and stifle weeds.
  • Find more tips for planting onions in different regions and soils.

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:

  • Fill a pot with potting soil and make a hole in the middle that is about the depth and width of the onion.
  • Place the onion in the hole and cover with soil.
  • Water and put the pot in a sunny spot.
  • 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.

Care

How to Care for Onions

  • Fertilize every few weeks with nitrogen to get big bulbs. Cease 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 mulch is used. About one inch of water per week (including rain water) is sufficient. If you want sweeter onions, water more.
  • Onions will look healthy even if they are bone dry, so be sure to water during drought conditions.

Pests/Diseases

  • Thrips: To control thrips—tiny insects about as fat as a sewing needle—take 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.
  • Onion Maggots: Cover your emerging onion crop with a fine mesh netting. Seal it by mounding soil around the edges. The onion maggot 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.

Harvest/Storage

How to Harvest Onions

  • Pull any onions that send up flower stalks; this means that the onions have stopped growing. These onions will not store well but can be used in recipes within a few days.
  • 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 them to speed the final ripening process.
  • Loosen the soil around the bulbs to encourage drying.
  • When tops are brown, pull the onions.
  • Be sure to harvest in late summer, before cool weather. Mature onions may spoil in fall weather.
  • Clip the roots and cut the tops back to 1 inch (but leave the tops on if you are planning to braid the onions).
  • Let the onions cure on dry ground for a few days, weather permitting. Always handle them very carefully—the slightest bruise will encourage rot to set in.
  • Allow onions to dry for several weeks before you store them in a root cellar or any other storage area. Spread them out on an open screen off the ground to dry.
  • Store at 40 to 50°F (4 to 10°C) in braids or with the stems removed in a mesh bag or nylon stocking.
  • Mature, dry-skinned bulbs like it cool and dry.
  • Don’t store onions with apples or pears, as the ethylene gas produced by the fruits will interrupt the onions’ dormancy. Onions may also spoil the flavor of these fruits (as well as potatoes).
  • A pungent onion will store longer than a sweet onion. Eat the sweet varieties first and save the more pungent onions for later.

Recommended Varieties

Onion varieties are classified into two categories: Long-day (better for cool climates) and short-day (better for warm climates).

Long-day Varieties

  • ‘Yellow Sweet Spanish’: large, round shape; yellow-white.
  • ‘First Edition’: high-yielding, stores well, flavorful, creamy-yellow
  • ‘Red Wethersfield’: flat bulbs that store well, white flesh, red-skinned

Short-day Varieties

  • ‘Stuttgarter’: sold in sets, early maturity with slightly flat shape, yellow
  • ‘White Bermuda’: extremely mild, with thick, flat bulbs; white
  • ‘Burgundy’: good table onion with mild, sweet white flesh, red-skinned

Wit & Wisdom

  • Practice crop rotation with onions. Learn more about crop rotation.
  • To make onions taste milder, soak them in milk or pour boiling water over the slices and let stand for 20 minutes. Rinse with cold water.

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

Recipes

Cooking Notes

Chopping onions can sometimes look like a daunting task: 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!

For more tips on using onions in the kitchen and cooking them correctly, click here.

Planting Times

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Reader Comments

Leave a Comment

About Onion Farming

Submitted by Krishan on

Hi... I want to know about timings, life cycles and climate conditions required for Onions and Papaya.

onions

Submitted by Phil T on

I have a pot full of green onions from last year. They are all bunched up together. Should I cut the tops off right above the roots and plant for more green onions or can I leave an inch or so of stalk an plant to get big onions. I'm not sure if that will work but I know cutting just above the root line works.

Onions

Submitted by Sherrie on

I've been trying to grow yellow and chive onions. The tops on both look like grass instead of the nice hearty stalks I see everywhere else. This is my first garden attempt, so I'm sure I did something wrong. Just not sure what. HELP.I know it's to late for this season but I want to try again next season.

growing onions

Submitted by Almanac Staff on

The best advice is above, but consider in particular: Soil should be organic and have the proper pH (onions like neutral pH, so betw 6 and 7 is usually fine). Start with sets, not seeds (seeds can take several seasons; sets are small onions and are usually available in packages at nurseries or loose in feed stores and the like). Remember that onions are daylight sensitive; start them early in spring (but see the warning about temperatures above). Keep the plot weeded and sufficiently watered. They really are relatively easy to grow. We hope this helps your next season!

I want to start onion plantation project

Submitted by George on

I want you to advice me on what to know before starting an onion plantation project.

Hardiness

Submitted by MARK on

We plant our onions in zone 9 in the fall, NOT SPRING.

zone 9 planting time

Submitted by Almanac Staff on

Thanks for noting!

Harvesting

Submitted by James Ireri on

Hi Sir/Madam,

My Red onions are ready to be harvested but it's drizzling almost every day. What can you advice me to do ? Or is there a way i can harvest and dry them ?

Please advice.

Kind regards,
James Ireri.

Harvesting Onions

Submitted by Almanac Staff on

Hi James,

You can still harvest onions when it’s wet, but they won’t cure as well during the drying process and might rot in storage. It won’t hurt your onions to be left in the ground for a little while longer, so wait until there is a dry day to harvest.

Flowers on my onions

Submitted by Joanne Barnes on

I planted Spanish onions and they have flowers on them what does that mean

onion sets

Submitted by Paulette on

Can you help me? I have very nice onions growing but they are going to seed. There is a big stem in the middle that grows into seeds I cut off that stem but the bottom The bulb is only about an inch around. What am I doing wrong? Two years ago I grew beautiful onions that were a really good size.....Paulette I live in Sk. Canada

onion bolting

Submitted by Almanac Staff on

Your onions are bolting, probably due to temperature fluctuations such as a heat wave or cold spell. It happens to the best of us gardeners. The onions are bolting because they might die and throwing out seed to reproduce before they die. Has it been hot? The only to prevent this is to keep the plants well watered in hot summer especially when heat waves strike.  If you try onions next year, remember that seedlings are less likely to bolt compared to bulb onions grown from sets.

Yellowing onions

Submitted by Connie on

My soil was too acidic at a 3. I added garden lime after planting to help, and watered it in. My onionsets are 6 inches tall and yellow the bulb being not much larger than when I planted them. Can I carefully dig them up, mix the soil to the. Right pH and replant them again?

roundup

Submitted by Judy Klein on

I want to use Preen between the rows in my garden. Will it damage the onion bulbs before they start to grow?

Preen

Submitted by Almanac Staff on

We’d recommend contacting the manufacturer for best advice. Looking at a label, it appears that for onions, they recommend applying Preen Garden Weed Preventer to the soil before transplanting onions. But best to double-check with them. Customer service number for Lebanon Seaboard Corporation that makes Preen is: 1-800-233-1067.
http://www.preen.com/labels/2463793.pdf

Onion farm

Submitted by Paul on

Hi to you all. I would like to thank for all this information about onion farming. My question is what are the key attacks (diseases) that I have to worry about, and how to deal with it.

onion pests

Submitted by Almanac Staff on

Hi Paul, See the Pests and Diseases section above on this page. We also provoide the links to more information.

overwinter onions

Submitted by BassCoach on

I live in a Chicago suburb and leave onion sets in the ground and cover with leaves all winter long. By mid April the green onions are ready for an early harvest. I just remove the soft outer portion,rinse and they're ready to eat.

Onion seeding

Submitted by Mr Magoo on

In the South, short day onions are seeded in late Sept to mid Oct. It is a little late but still possible to plant directly or plant a bed to transplant sets in late Nov. There are many varieties, but Yellow Granex types are popular with names like "Century" & "Sapelo Sweet". There are also red varieties that are either sweet or pungent in the short day type, with names like "Red Hunter & "Chianti", respectively.

Gardening tips

Submitted by Bud Redden on

I am so impressed with all your data for planting, maintaining and harvesting vegetable. I am so glad I found your articles on line. I hope to be a good gardener as I love gardening vegetables, flowers, shrubs and trees. Thank you kindly.

caltivation of onion

Submitted by neumani munuo on

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

Soil testing

Submitted by jim on

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.

Would like to keep up on

Submitted by Eugene Dodge on

Would like to keep up on ideas !

bulb size

Submitted by Dick on

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.

small onions

Submitted by Almanac Staff on

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!)

Bulb Size

Submitted by Dwight James on

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...

Your info on growing onions

Submitted by Laura on

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

growing onions

Submitted by Gerrit on

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

Protecting Onions

Submitted by Almanac Staff on

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. 

Yellow onion

Submitted by Dihann Lehman on

My onions are flowering is this ok

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Growing Onions

Botanical Name

Allium cepa
Plant Type Vegetable
Sun Exposure Full Sun
Soil Type Any, Loamy
Soil pH Neutral
Bloom Time
Flower Color
Hardiness Zones 3, 4, 5, 6, 7, 8, 9
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