Onions are a vegetable used nearly daily in many of our kitchens. Onions are a cold hardy crop that grows well in the zone 3 gardening climate of Canada and other parts of the northern hemisphere. Onions belong to the allium family and can be beneficial in your garden as a companion plant to many plants as a pest deterrent. (See below.)
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It is sad to admit, but personally I have struggled with growing large onions in my garden. Last fall, the onions I harvested were only slightly larger than my garlic. With a little research and some new knowledge I am confident that this year will be more successful. Let me share with you a few tips for growing onions that I have found out in the last year!
These are the 3 mistakes I believe I have made when growing onions.
#1 Possibly growing varieties other than long-day onions.
#2 Planting too late in the spring. (End of May vs. end of April).
#3 Planting the bulb too deep.
Here is what I have learned that has led me to believe I was making these mistakes with my onions.
Long Day vs. Short Day Onions
Onions are photothermic. That means they need enough hours of daylight to grow to their full potential.
One of the most exciting tips I have learned for growing onions is that there are long-day, intermediate-day and short-day onions. Up here in the northern hemisphere (or in latitudes 37–47°), where the summer days are long and winter days short, I need to be growing long-day onion varieties! Long-day onions require 14 to 16 hours of daylight to mature. Near the equator intermediate-day onions grow best and in the southern hemisphere, short-day onions.
As long-day onion bulbs grow quickly when there are more hours of sunlight in the day, it is beneficial to plant onions as soon as the soil is workable and night temperatures are warmer than -6C (20F). With June 21st being the longest day in respect to hours of sunlight, planting onions earlier allows them to get the most out of the long days.
Onions are Cool Hardy
Onions are cool hardy and tolerate light to medium frost, and even snow, well. To grow larger onions, plant onions up to 4 weeks prior to the last expected frost.
I grew some onions from seed this year and tested this by planting some of my onions out on May 1st. They had frost on them multiple times and snow on them 2 or 3 times. I planted other seed onions May 4th. Now it is only June 4th but the ones I planted outdoors earlier are looking stronger and healthier than the ones I planted out later. I did not cover my onions during the frost or snow. During that time, it got down to -10C (14F). Although the onion tips received a little frost bite, the rest of the plant remained strong and healthy.
Onion Bulbs are Not Part of the Root System
For some reason I had assumed that the bulb portion of the onion was part of the root and was planting my onions too deep, thinking this would help the bulb grow larger when in fact, onions should be planted no deeper than 1 inch beneath the surface of the soil. As the bulb develops it will push soil away and 1/2 to 2/3 may end up exposed above the soil. Do not cover the exposed portion with more soil.
The onion bulb is technically not root or stem but rather a tunicated bulb, or a modified stem where the fleshy layers of the onion bulb store food and transfer this to other parts of the plant when needed.
Onion Sets or Seeds?
Onion sets are small onion bulbs that have been grown from seed, dried, and packaged to plant the next season. Onion sets are preferred by many as they are easy to plant and work with. If you wish to grow onions from seed, they should be started indoors in mid to late January. (Find my full printable seed starting guide here.)
Onions are biennial. This means they form seed heads in their second year of growth. Some feel onion sets are at a disadvantage because they may put energy into forming these seed heads instead of bulb growth.
This is my first year growing onions from seed. I am curious to see what ends up larger at harvest, seed or bulb onions.
Find my printable seed starting guide here.
How to Plant Onions
If possible, choose a full sun location to grow your onions.
Plant onions in loose, well drained soil.
Make a hole about the size on the onion.
Plant onions 4 inches apart and 1 inch deep with the root end facing down.
Cover onion with soil.
Water immediately after planting and continue to water as needed afterward.
Once onion tops are about 4 inches tall they can be harvested and used as green onions. Choose an onion that has at least 3 green tops and cut one of them about 2/3 the way down. Taking too many onion tops from one plant may stall onion bulb development.
List of Long-Day Onions
Long Day Onion Varieties
Early Yellow Globe
Rossa d'Inverno Rubino
Southport White Globe
Southport Red Globe
Sweet Spanish Utah
Yellow Sweet Spanish
Onion Companion Plants
Plant onions next to beets, brassicas (cabbage, broccoli, cauliflower & brussels sprouts), chamomile, cucumbers, dill, kale, leeks, peppers, potatoes, summer savory, spinach, squash, strawberries or tomatoes.
Avoid planting near asparagus, peas and beans.
You can find my full printable companion planting guide here.
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