Growing Onions: A Complete Profile
By Growing Home Greens Team · July 18, 2026
Onions are one of the slower crops in the garden, around 100 days from transplant to harvest, and they start life indoors well before most of the garden is even being planned, which catches a lot of first-time growers off guard. There’s no shortcut here: get the timing right up front and the rest of the crop mostly takes care of itself.
Starting it indoors, months before the ground is ready
Start onions indoors about 8 weeks before your last frost date and set transplants out roughly 3 weeks before that date arrives. They tolerate a light frost fine. Onions are also one of the few crops planted dense: 9 per square foot, packed in tight, since each plant only needs room for a single bulb rather than sprawling foliage. Which variety bulbs up properly in your area depends heavily on day length (short-day, day-neutral, or long-day types are matched to latitude), so check what’s sold locally rather than assuming a variety that worked for a neighbor two states away will perform the same for you.
Thin bulbs mean the wrong day-length type
Thin, scallion-like bulbs at harvest are usually a day-length mismatch, the wrong type of onion for your latitude never gets the trigger to bulb up properly, no matter how well it’s otherwise grown. Bulbs that rot in storage often started with damage at harvest; let the tops fully flop over and the necks dry out before pulling and curing.
A dense edge crop that helps its neighbors
Onion’s sulfur scent is reputed to confuse pests looking for carrots and brassicas by smell, which is why it shows up as a companion across several other profiles. See the full companion guide for onions. Its dense 9-per-square-foot spacing makes it a good edge or border crop in the Garden Designer, and because it occupies a bed for the better part of a season, plan around what else needs that square footage before and after it.
Companion planting guide for Onion · Find your planting dates
Typically viable in USDA zones 3-10. Not sure your zone? Look it up by ZIP code.
Method: Start indoors: Start indoors from seed, then transplant outside. Onion needs a head start most zones can't give it by direct-sowing alone.
See exact start-indoors, direct-sow, and harvest dates for your zone →
How many Onion plants fit per square foot?
Spacing: 16 per square foot (square-foot-gardening spacing). Mature height: 1-1.5 ft.
Soil & water: pH 6-6.5. well-drained. Amend with lime if soil pH falls below 6.
Varieties worth considering
- Texas Grano 1015Y: A short-day onion bred at Texas A&M specifically for the South, a solid pick for warm, short-winter-day zones like 9b where long-day types never get the daylight trigger to bulb properly. (source)
- Copra: A long-day storage onion rated 4.9 stars in Cornell's Vegetable Varieties for Gardeners database, the top-rated onion in their system, with a thin neck and hard, dark yellow skin built for keeping through winter. The one to grow in a northern, long-day zone if Texas Grano's short-day type won't even bulb for you. (source)
- Ailsa Craig Exhibition: Also highly rated in Cornell's database at 4.5 stars, a large, slightly oval long-day type prized for sweetness over long storage life. Choose it over Copra if fresh eating quality matters more to you than months in the pantry. (source)
- 'Walla Walla Sweet' (best for: fresh eating, not storage): Johnny's lists this long-day Northwest classic as ultra-mild and juicy, best fall-planted where winters stay above -10°F, but explicitly not a storage onion the way Copra is. Grow it if fresh eating quality is the goal and you'll use the crop within weeks of harvest rather than through winter. (source)
Cited from the source shown next to each variety. We haven't grown these ourselves yet, so treat this as a research-backed starting point, not a personal endorsement.
Where to buy onion seeds
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See it growing
Search YouTube for "growing onion" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
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Growing Onion: A slow, ~100-day crop started from seed indoors months before it ever touches the ground outside.
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