How to Grow Onion
Onion At a Glance
Difficulty
Easy
Category
Vegetable
Sun Exposure
Full Sun
Frost Tolerance
Frost Hardy
Cold Hardiness
Survives to -12°C
Plant Family
Amaryllidaceae
Growing Season
Cool Season
Plant Lifecycle
Biennial
How to Start It
★ Recommended for beginners
Sets are tiny onion bulbs grown the year before, and they are the easiest, most forgiving way to grow onions. Plant them about 4 weeks before your last spring frost, as soon as the soil can be dug, pointy end up, 2 cm deep and 10 cm apart, with just the tip showing. Pick sets no bigger than a marble, since big ones tend to flower instead of making a good bulb.
Onions form their bulbs when the summer days get long, so in Canada pick long-day varieties, or the bulbs stay small. Big, firm storage onions keep for months, and you can pull a few early to use as green onions.
When To Start
Onion likes cool weather. Sow it in early spring, as soon as the ground can be worked.
We do not have exact sowing dates for this one yet.
When should you plant Onion?
Your planting dates depend on your local climate. Sign up and add your location to unlock personalized dates.
Your Onion Planting Window
Start planting
May 15, 2026
Last chance
Sep 10, 2026
Your Onion Calendar
Set your location to turn these into exact dates and reminders.
Optional: start onion seeds indoors for bigger bulbs
10 weeks before your last frost· optional
Plant onion sets or young plants outdoors now
4 weeks before your last frost
Onions are ready when most tops have flopped over
110 days after your last frost
Did you water your onion seedlings today? Keep the top of the soil damp until they are up and growing.
About 1 days after you plant it
Time to thin the onion seedlings: snip the extras at soil level so each one has room to grow.
About 24 days after you plant it
Your onions are growing! Keep weeds away, onions do not like to share space.
About 51 days after you plant it
Nice work! Leave the soil loose around the bulbs so they have room to swell.
About 87 days after you plant it
Picking time may be here: check your onion.
About 110 days after you plant it
The Journey Ahead
Onion's Lifecycle
Seedling
Mature Plant
Seed Production
Step 2
Planting & Sprouting
Expect sprouts in 7–14 days
Growing Tips
- 1Grow onions in full sun, at least 6 hours a day, in loose soil with compost mixed in, since their short roots cannot push through hard ground.
- 2Water evenly about once a week, then stop watering once the tops start to fall over, so the bulbs can firm up for storing.
- 3Feed with compost tea every 2 to 3 weeks until the bulbs begin to swell, then stop.
- 4Keep the bed free of weeds, which crowd out the thin onion leaves, and never pile soil over the bulbs, which like to sit at the surface.
- 5Cover young plants with row cover to keep off the small flies whose grubs tunnel into the bulbs.
- 6Onions are toxic to cats and dogs, so keep chewing pets away.
Seedling Phase
Step 3
Growth & Maturity
~110
Days to Maturity
45 cm
Mature Height
10 cm
Mature Width
Pests to Watch For
Diseases to Watch For
Mature Plant
Step 4
Harvesting
Harvest Window
14 days
When to Pick
Harvest when the tops yellow and flop over in mid to late summer
How to Harvest
- 1Onions are ready when most of the tops have yellowed and flopped over.
- 2Ease the bulbs out with a fork on a dry day and lay them on the soil for a day or two.
- 3Cure them in a dry, airy, shaded spot for 2 to 3 weeks, until the necks are dry and the skins rustle.
- 4Trim the roots and cut the tops to about 2 to 3 cm, then store them in a mesh bag somewhere cool, dark and dry.
- 5Use any with thick necks first, since those do not store well.
Step 5
Saving Seeds
How to Save Seeds
Onions are biennial: they make a bulb the first year and flower only in the second. Store a few of your best bulbs over winter somewhere cool and dry, then replant them in spring, and each will send up a tall stalk with a round flower head. Bees cross onions with other onions of the same kind, so let only one variety flower within about 800 m, and let at least 6 plants flower together. Hybrid F1 seeds will not grow true, so save only from a variety that is not a hybrid. When the heads dry and you see black seeds, cut them into a paper bag, let them dry for another 2 weeks, then rub the seeds out. Onion seed is short-lived, so store it labelled in a cool, dark, dry place and use it within 1 to 2 years.
Seed Production
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