Onion is a perennial grown for the harvest, ready about 110 days after sowing. It's hardy across USDA zones 2 through 11 and stands up to deer. Its summer flowers are a moderate draw for honeybees, native bees, and butterflies, even though the harvest is the prize. As an allium (the onion family), give it a fresh bed each year — away from where its relatives just grew — so the soil-borne pests and diseases of the family never get a foothold.
Onion — the short answer
Onion: grown in zones 2–11, full sun, pH 4.3–8.3, about 110 days to maturity.
- USDA zones
- 2–11
- Manual horticultural correction (source not retained); NC State Extension and Missouri Botanical Garden, with the remaining rows from other published sources or Growable Ground compilation
- Soil pH
- 4.3–8.3
- FAO ECOCROP
- Sun
- Full Sun
- Growable Ground Plant Database
- Days to Maturity
- 110 days
- UMass-Veg
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS and university Extension sources — each tile names its own row's source, because per-field provenance varies.
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See Onion
What Onion is
Onion grows as a perennial and reaches around a foot and a half at maturity. It blooms white in summer. It's also deer-resistant.
How to grow Onion
Onion grows in USDA zones 2 through 11 and is ready to harvest about 110 days after planting. Onion does best in full sun — at least 6 hours of direct sun a day — and soil from pH 4.3 to 8.3, on well-drained ground. It needs around 1,700 growing degree days to mature and a growing season of at least 85 frost-free days, which is why climate matters as much as soil.
USDA Zones
2-11
USDA PHZM 2023
Soil pH
4.3 - 8.3
FAO ECOCROP
Sun
Full Sun
Growable Ground plant catalog
Drainage
well (dry spells)
Growable Ground plant catalog
Minimum Growing Temperature
39.2°F
Below this it stops growing rather than dies — a pace limit, not a survival limit.
FAO ECOCROP
Days to Maturity
110 days
From transplanted sets/starts; bulb sizing depends on day-length match.
UMass-Veg
GDD Required
1700+
Growing degree-days of accumulated warmth it needs to mature — humid summers reach this faster than cool coastal ones.
Growable Ground plant catalog
Mature Height
1.5 ft
Growable Ground plant catalog
Frost-Free Days
85+
The frost-free stretch it needs start to finish — short-season areas may need an indoor head start.
Growable Ground plant catalog
Start the season right
Plant onion in full sun with at least 6 hours of direct sun. It grows in the cool halves of the year, so sow it in spring or late summer rather than waiting for midsummer heat.
Match the soil
Onion prefers pH 4.3 to 8.3 (FAO ECOCROP). A quick soil test from your local Extension lab tells you whether to add lime or sulfur to land in band.
Water steadily
Keep the root zone evenly moist through establishment. A 2–3 inch mulch layer holds moisture without waterlogging.
Harvest at maturity
Onion is ready about 110 days after sowing (UMass-Veg). Watch for cultivar-specific ripeness cues and pick at peak.
Where Onion thrives
On hardiness alone, onion grows across most of the country — its range (USDA zones 2 through 11) is unusually wide. Zone is only the starting point, though: the soil pH, drainage, and frost dates on your specific land decide how well it actually does.
A USDA zone is a 10°F band of average annual extreme winter minimum, so zones 2–11 spans average winter lows from -50°F to 50°F (USDA PHZM 2023). Across the 50 states and DC, that band covers 48 outright and splits 3 more down the middle — and which side of that line your land sits on changes the answer.
Two different numbers hide in that range: zones 2–11 is where onion is GROWN, but it survives winter in the ground only down to zone 5 (NC State Extension Gardener Plant Toolbox; Missouri Botanical Garden Plant Finder). Colder than that, it is grown as an annual or brought under cover.
Zones 2–11·Where Onion growsOpen map →
Continental US shown — Alaska and US Pacific territories sit outside the federal map's polygon dataset.
Where Onion stands, state by state
Onion is rated for zones 2–11 — a cold floor USDA puts at -50 to -40°F. Across the 50 states and DC, 48 sit fully inside that band, the line runs through 3 more, and 0 sit outside it — and inside every split state, the same line runs on at county grain.
Fully inside zones 2–11
48 states
3 of 48 shown
State zone extents: USDA Plant Hardiness Zone Map (PHZM) 2023. A zone is a 10°F band of average annual extreme minimum temperature, so a state that splits the band contains the boundary — its own page draws the county line, and a parcel report resolves which side your land sits on.
What grows around Onion
Growing guides for onion
In rotation planning, onion counts as a Allium — beds recover best when allium crops don’t follow each other in the same spot year over year. (Growable Ground derivation — crop-rotation group from botanical family)
Related plants in vegetable
Good to know
One caution for pet owners — onion is toxic to dogs and cats (moderate severity). Keep it out of reach, and call ASPCA Animal Poison Control at (888) 426-4435 in an emergency. (Source: ASPCA.)
Onion offers moderate value to bees and other pollinators. (Source: Pollinator Partnership.)
Before you harvest onion, know your soil
Anything you grow to eat takes up what's in the ground it grows in, so it's worth knowing what's documented near you before you plant onion for food. Our free screen reads 9 federal source types across roughly 1.8M indexed sites and shows which sit near your address and which way they drain. It's a screening estimate from public records and proximity — not a soil test — so a nearby record means a soil test is worth it, not that your soil is unsafe.
Your land is one point inside Onion's range
This page resolves to the species. Your state page draws the county line, and a report reads the parcel — the soil pH, drainage, sun, and frost dates on your exact ground, which no species average can see.
See if Onion will thrive on your land
Zone averages are a start. Your exact soil pH, drainage, sun exposure, and frost dates shape whether onion actually takes — we score it against the real conditions at your address.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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How we know this about Onion
The figures above are cited per row, not per site: the pH band names this plant’s own source column, the three temperature figures each carry their own, and days-to-maturity cites the publication that actually lists it. All of it comes from the Growable Ground Plant Database — a compilation over FAO ECOCROP, USDA PLANTS, and university Extension sources, published openly with per-field provenance.
Grounded inUSDA PLANTS Database•USDA PHZM•ASPCA
Frequently asked questions
Can I grow Onion in my zone?
Onion grows in USDA hardiness zones 2 through 11 (USDA PHZM 2023). Zone is one factor — soil pH, drainage, and frost dates on your specific parcel also shape whether it takes.
How long does Onion take to grow?
Onion is ready to harvest about 110 days after planting (UMass-Veg). Your local frost dates and soil temperature move that window earlier or later.
When should you plant Onion?
Onion is a cool-season crop, so it goes in during the cool halves of the year — early spring, and again in late summer for a fall planting — rather than at the height of summer heat. Your local frost dates set the exact window — a Growable Ground report reads them for your address.
How much sun does Onion need?
Onion needs full sun — a spot that catches at least 6 hours of direct summer sun a day. In more shade it still grows, but usually gives a smaller, later crop. The catch is that a yard rarely gets even light everywhere — a fence, the house, or one tall tree can quietly take those hours. A Growable Ground report reads the real sun-hours across your land, canopy and buildings included, so you can pick the brightest bed before you plant.
What soil does Onion need?
Onion prefers soil pH 4.3 to 8.3, on well-drained ground (FAO ECOCROP). Your report scores your parcel's actual soil against that using USDA SSURGO data.
Does Onion attract pollinators?
Yes — onion's flowers are a solid nectar source for honeybees, native bees, and butterflies. (Source: Pollinator Partnership.)
Is Onion safe for pets?
Onion is toxic to pets (dogs,cats) with moderate severity. Keep it out of reach, and call ASPCA Animal Poison Control at (888) 426-4435 in an emergency. (Source: ASPCA.)