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.
What to expect
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 genuinely dense: 9 per square foot, packed in tight, since each plant only needs room for a single bulb rather than sprawling foliage. Which variety actually 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.
Common problems
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.
Where this fits in your garden
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 →
Spacing: 9 per square foot (square-foot-gardening spacing).
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)