Onions are a cool-season crop and can be planted as soon as the soil is workable; as early as 4 weeks before the first frost free days. In Manitoba, our average first frost free date is May 24, so onions could go in around April 20th if the soil is ready. Even if the green tops start poking out, onions can take frost or even a layer of snow.
Why Plant Onions Early?
Did you know that onions are photothermoperiodic? Cool word, but what does it have to do with planting onions? It means onions are sensitive to light and temperature, in other words, onions need to get enough hours of daylight at the right temperature for optimum growth.
Long-day onions (white, yellow or red cooking onions) – the kind we grow here in Manitoba – need about 13 to 16 hours of light daily during bulb formation (early May to July). We need to get our onions in the ground as early as we can to meet those daylight requirements. Remember the longest day of the year is June 21 and daylight time decreases after that.
Get onions in as soon as the soil can be worked and overnight temps are higher than -6°C (20°F) to take advantage of those long days. I usually plant mine sometime between April 20 and May 5 – depending on temperature, soil temperature, soil moisture, etc.
If you’ve ever planted onions and wondered why you’re bulbs were so tiny – not enough daylight is likely the main culprit.
How to Get Bigger Onion Bulbs:
- Ensure they aren’t shaded, as stated above, onions need the maximum number of hours of daylight to grow big bulbs.
- Provide adequate space between onion bulbs, 3-4 inches (even though the bag may say 1 inch, as mine did).
- Remove weeds that may compete for light and/or moisture.
- Ensure sufficient moisture during bulb formation especially – onions won’t look like they need water (ie they won’t wilt), but they do!
- Plant early enough in the season to ensure onions will get enough hours of daylight.
- Plant the right variety for your area – long-day (north), intermediate-day (central) and short-day (south). Buy local and check the label to be sure your onion sets are sourced from your region – Canadian sourced onion sets will most likely be long-day onions unless specifically labelled otherwise.
- Loosen the soil so the soil is not too compact for the bulb to grow.
How to Plant Onions
It is easiest to grow onions from onion”sets” – immature onion bulbs. If you prefer to start from onion seeds, they must be started in doors very early in the year. One little onion set will grow into one big onion, so plant as many sets as you want to harvest. Put the onion with the root side down and the pointy side up in the soil.
When to Plant: Early, 4 weeks before last frost free day (end of April to mid-May in Winnipeg) – when soil is workable
Days to Maturity:75-110 days depending on variety, green onion tops can be harvested within 3 weeks
Where to Plant: Full sun is best in well drained, fertile soil
How to Plant Onions: With pointy tip up, place sets in soil and cover with 1″ (2.5 cm) of soil. Don’t go too deep!
Spacing Between Sets:space 3-4″ (8 cm) apart so each bulb has plenty of space to grow
Spacing Between Rows: space rows;12-16″ (30-40 cm) apart
Depth of Set: 1″ (2.5 cm) deep
Companion Seeding: Seed onions next to cabbage, broccoli, kale, kohlrabi, brussel sprouts, tomatoes, celery, carrots, beets, peppers, spinach, parsnips, strawberries. I like planting onions next to my carrots with the hope that the onions keep carrot flies away – I’ve never had them, so I keep this partnership alive!
NON- Companions: Avoid planting onions next to beans, peas, sage and asparagus
Here are some random photos of onions growing in our garden.
More Tips for Planting Your Garden
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