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  1. There are many different kinds of onions. Onions are a cool season crop and most need a long growing season to fully mature.
  2. Onions have different characteristics, depending on the cultivar. Some are good for cooking, others for storage, and others still for colour, sweetness or flavour.
  3. Onions can be grown from sets or transplants. Sets are immature onions that are planting into the soil. Some short season onions can be seeded directly into the garden.
  4. Spanish or sweet onions need a long growing season and must started indoors about 8 weeks before transplanting into the garden.
  5. Yellow onions are the easiest to grow and are best for storage.
  6. For a quick crop of green onions, try growing scallions.

     

Onions belong to the Alliacease family. This family includes garlic, onion, scallions, shallots, leeks and chives. The genus name is allium which is the Latin word for garlic. These plants are known for the organic sulfur compounds that give them their unique flavours.

Since all of these plants share a common ancestor, they all have very similar growing needs and are prone to similar problems.

While they are quite similar, there are some key differences, so to ensure best success so we've broken these into separate articles for easier instruction.

Onions are high in vitamins C and B6, as well as folate and thiamine. Check here for detailed information from the USDA National Nutrient Database for Standard Reference.

The Canadian Food Guide recommends that roughly half of the food on your plate should be fruits and vegetables.

Canada Food Guide: What's On Your Plate?

 

Growing outdoors

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Onions prefers to grow in a rich, sandy, sandy loam or loam soil high in organic matter. Avoid planting onions in low-lying spots that are prone to waterlogging after it rains. 

Onions needs full sun for best growth. Onions are not suitable for part sun, partial shade or shady areas.

Onions are best grown outdoors in the ground in raised or unraised/ground level gardens if the soil is suitable. Onions can also be grown in a container both indoors and outdoors. Supplemental lighting is needed for growing onions in indoor containers.

Onions are not typically suitable for most hydroponic, straw bale, or other alternative growing methods.

When to plant depends on the type of onion you are growing. See the "Recommended Cultivars" tab.

Spring planting

Onion seeds can be planted around the last expected average frost free date in your area.

Although onion sets and transplants are tolerant of cooler temperatures and you can plant early in spring, plant them a bit later to avoid root maggot flies. A rule of thumb is to plant sets and transplants after caragana bushes bloom - by this time the maggot fly activity is reduced.

  • Knowing the last expected spring frost date for your location will help you plan when to plant. The date is based on averages and varies according to where you live – it is as early as mid-May for Saskatoon, Estevan and Swift Current, SK, while Yellowknife is May 30 and the Moosonee region in Manitoba is June 10. Find the date of the last spring frost at this link: https://climateatlas.ca/map/canada/lastspring_baseline# Click on where you live on the map.

Onion sets germinating

Starting transplants from seed

Spanish or sweet onions need a long number of days to maturity and should be started as transplants indoors at least 8 weeks before your last average spring frost date in your area. 

Planting sets

Sort through the sets and discard any that are damaged or diseased. Plant individual sets 2.5 cm (1") deep with the pointed end facing up. Space them about 7 - 8 cm apart (3") within the row. Allow about 30 cm (1') in between the rows.

Direct seed

Check the information on your seed packet for planting. 

 

Don't forget to label what you planted. It's also helpful to draw a map to help you track planting locations and success each year. This information is critical if you're rotating your crops to help prevent insect and disease issues.

Onion terminology and types:

Spanish or sweet onions: There are many cultivars including cooking onions. Sweet onions tend to be larger such as 'Sweet Spanish' and 'Walla Wall'. All require a long growing season and must be transplanted. Most do not store well.

Yellow and red onions: These can be direct seeded, planted as sets, or grown from seeds indoors and transplanted outdoors. White onions usually require short growing days and do not grow well to maturity on the prairies or far north.

Bunching onions or scallions: These can be direct seeded and are harvested young, like spring onions.

Storage onions: These keep for a longer period of time after harvest. Yellow storage onions are the easiest to grow and are best for storage.

Multiplier onions: These are a group or cluster of onions held together in a bulb. The sets are separated and planted individually, and will form bulbs in summer. They can also be harvested early as a green onion before the bulbs form, or allow the bulb to mature and harvest later.

 Cultivar recommendations:

  1. Here are cultivar recommendations from the North Dakota State University Cultivar Trials, as they share a similar prairie climate and soils. You may download their list here: North Dakota State University Vegetable Cultivar Recommendations for 2021
      • Ailsa Craig, Candy, Copra, Sweet Sandwich, Walla Walla
  2. The following cultivars are recommendations from the University of Saskatchewan vegetable program field trials which were conducted from 1989 through 2016. 
    • Spanish onions: Delgado, Exhibition, Kelsae Giant, Riverside Sweet Spanish, Teon Hybrid, Vison
    • Red onions: Grateful Red, Mars, Mercury, Red Hawk, Red Beauty, REd Bull, Red Burgermaster
    • White onions: New Mexico White, Sterling, White Wing
    • Yellow onions: Anillo, Braddock, Burgoes, Calisto, Copra, Crocket, Daytona, Festival, Frontier, Infinity, Madras, OLYX08-640, Safrane, Sedona, Sturon Organic, Sherman, Talon, Tamara, Teton, Timberline, Trailblazer, Yula
    • Bunching onions: Evergreen Ishikura Improved, Evergreen Long White Nebuka, Kincho, Long White, Parade, Red Spark, Tokyo Long White
    • Storage onions:
      • Spanish: Calibra, Crockett, Harmony, Ovation, Ringmaster, Teton, Vision, White Sweet Spanish
      • Red: Mars, Mercury,  Red Beauty, Red Burgermaster
      • Yellow: Cannon, Copra, Festival, Fortress, Frontier, Genisis, Mustang, Nebula, Nobility, Prince, Sturon Organic, Tahoe, Talon, Timberline
Onions require plentiful, even moisture for good yields.
  • Onions compete poorly with weeds especially when they are small, so stay on top of weeding and consider mulch for pathways. Besides weeding, onions are fairly low maintenance. They do not require a lot of fertilizer and are usually free of insect and disease problems.
  • Onions do best with an ample supply of water, about  2.5 cm (1") of water per week for most soils. Sandy soil may require additional water during hot dry weather.
  • Use mulch to retain moisture and suppress weeds.
  • Onions are not drought tolerant and are shallow rooted so must water fairly often. Watering is especially important when the bulbs are expanding.
  • Water early in the day to allow time for the foliage to dry before nightfall in order to reduce disease susceptibility.
  • As bulbs mature, the bulbs tend to push out of ground. This is normal. Their roots are below the bulbs. Do not cover the bulbs with soil, especially the neck.
  • Reduce watering in the fall. See the "How to Harvest" tab.

Onions can be fall seeded once it is cold enough that seeds will not germinate.  See: Fall seeding

You can also plant sets in late fall in much the same way as you would do fall seeding. It is especially important to mulch sets deeply after planting for best winter survival. Be sure to mark the rows too.

Onions are a good crop to grow in the far north with the exception of Spanish or sweet onions that require a long number of days to maturity. 

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Forgot what you planted? Not sure if it's a weed? Germination in onion

See our preservation section for more videos.

Growing in containers

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Onions can be grown in a container outdoors. Choose a generously sized container with a hole in the bottom for drainage. Space onions in a grid as per the instructions for planting in the ground.

See: Vegetable container gardening

See our Growing indoors page for detailed growing advice.

Scallions or bunching onions work well in containers, as do onions grown from sets.

Saving seeds

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Seeds are expected to be shelf-stable for one year from date of sale if purchased from a reputable retailer. If you wish to save your seeds beyond that, store them in a sealed jar in the fridge. Seeds lose viability more quickly if they are too humid, too dry or too warm.

The life expectancy of onion seed stored under favourable conditions is one to two years.
 
Seeds stored under less favourable conditions will show poor germination after just a single year of storage. Beyond this, you can expect your germination rates to go down (ie. not all of your seeds will grow, but some might). To test your seeds, you can do a simple germination test. Follow the link for instructions. If you are still getting some seeds germinating, seed more thickly and thin any extra.

We do not recommend saving seeds from onions. Onions are biennials. This means that they do not produce flowers in their first year's growth. Instead, onions will collect energy in the form of natural sugars and store it in their bulb during the first year's growing season.

Sometimes onions prematurely produce a flower stalk in their first growing season if they are exposed to large fluctuations in temperatures. Flower stalks usually result in smaller bulbs or sets because energy goes into flower and seed production. If bolting occurs, you can allow the flower to fully mature until it becomes dry. Harvest seeds once the flower is completely dry.

Harvest

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Reduce watering in fall. A dry autumn season is desirable because it allows the bulb to go dormant. Ideally, the leaves should start to brown and the neck of the bulb starts to dry naturally.

Harvest onions after the necks dry and fall over naturally.

If the tops are not drying down naturally in fall, (perhaps due to wet weather) then gently stomp on onions to break the necks.  This is not ideal as it can leave an open wound that is susceptible to fungal diseases. Take extra care when curing these onions to make sure the neck is dry.

 



 

Onions are ready for harvest when 1/3 to 1/2 of the tops have dried and fallen over. Dry tops prevent bacteria and disease from getting inside the bulb. You can bend over the tops when the onions are in the ground to speed this up. Once they are ready, loosen soil with a fork to remove the onions taking care not to pierce the bulbs and gently life the plants

 

 

 

Storage

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Curing onion bulbs

Onions need to be cured (dried) before storing. Trim off the (dry) tops to 3 – 4 cm (1 ½" - 2"). Set onions on a layer of newspaper or ventilated racks in a warm (at 27°C is ideal), dry, sheltered place for about a week.

Check the onions regularly to see if any are mouldy and remove them right away. Once they are dry, gently remove the roots (which should be dry) and any loose outer papery skin.

Properly cured onions should store 3 - 5  months.

Thick necks

Onions with thick necks are immature and will not store properly even if cured. The necks are just too thick to dry and cure properly for long term storage. Leave these in the soil as long as you can or eat them right away.

Thick necks caused by:  a late maturing variety which has had an insufficient number of long days for maturity, excess applications of nitrogen fertilizer and/or excess moisture. Thick necks are common in Spanish and sweet onions.

You can store properly cured onions for 3 - 5 months.

Place the onions in mesh bags, baskets or any box (plastic or cardboard) with slats or holes. They will last longer if they are not piled up too much and have good air circulation. Store in a cool, dry and well ventilated area in your home. Optimal temperature is 10°C and 60% - 70% relative humidity, which is fairly dry.

If you don't have a root cellar, use a thermometer to check other spots in your home: a cupboard, pantry, closet or shelf in the kitchen or a spare room are potential places to store these vegetables. The key is that the temperature should not fluctuate. Avoid placing onions too close to exterior walls, windows or hot air vents. 

Onions stored longer than 5 months may begin to shrivel or sprout.

See our cold storage page for detailed advice on finding a suitable storage location and choosing storage methods.

Other preservation methods we recommend include freezing, fermenting, dehydrating (drying) or canning.

Cooking and preserving

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Preservation methods we recommend include freezing, fermenting, dehydrating (drying) or canning.
Dehydrating onion

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This method for making powdered tomatoes can be used to make onion powder too

Alternative ways to eat common vegetables

 

Troubleshooting

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Onions are relatively low maintenance. Providing their water, light and soil needs are managed they don't tend to get a lot of issues. Watering deeply once a week and keeping weeds picked will go a long way towards preventing most issues.

Onion root maggot can be a problem.

See the Common problems tab on this page for advice on this and other specific garlic issues.

 

 

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Common questions

Research and student activities

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