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.
Zones
2-11
pH Range
4.3-8.3
Sun
Full Sun
Days to Maturity
110
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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
USDA PLANTS Database
Sun
Full Sun
plant_species_v5.csv
Drainage
well (dry spells)
plant_species_v5.csv
Frost Tolerance
39.2°F
plant_species_v5.csv
Days to Maturity
110 days
From transplanted sets/starts; bulb sizing depends on day-length match.
UMass-Veg
GDD Required
1700+
plant_species_v5.csv
Mature Height
1.5 ft
plant_species_v5.csv
Frost-Free Days
85+
plant_species_v5.csv
Start the season right
Plant onion in full sun with at least 6 hours of direct sun, once the soil has warmed and frost risk has passed.
Match the soil
Onion prefers pH 4.3 to 8.3 (USDA PLANTS Database). 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.
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: Xerces Society, Pollinator Partnership.)
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.
Zones 2–11·Where Onion growsOpen map →
Continental US shown — Alaska and US Pacific territories sit outside the federal map's polygon dataset.
On USDA hardiness-zone overlap, Onion can grow in these states:
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:
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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?
Most growers plant onion after the last spring frost, once the soil has warmed, leaving enough of the season for its 85-day frost-free need. 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 (USDA PLANTS Database). 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 (Xerces Society, 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.