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When to plant Onion (bulb)

Computed from land-grant Extension planting-window rules (cited below), localized to real ZIP-level median frost dates, not a single national guess. These are national-generic rules by hardiness class; individual state Extension offices layer their own regional adjustment on top (earlier in the Deep South, later in the Upper Midwest). Enter your ZIP for your own dates, or read the four representative locations below.

Planting windows and crop timing here are computed from USDA/NOAA climate data and the university extension sources cited below, not a site visit or soil test. Treat this as a starting point: local conditions vary, and a local nursery or extension office can advise on your exact site. See our full Disclaimer.

Representative timing, by climate band

When to plant Onion (bulb) in four US climates

Each column is the most nursery-dense location in our directory within that USDA zone band, computed from that location's own real median frost dates, not a made-up example.

Stage Zones 1-5 (cold winters)
Fort Plain, NY 		Zones 6-7 (temperate)
McMinnville, TN 		Zones 8-9 (warm)
Apopka, FL 		Zones 10-13 (hot, frost rare or absent)
Loxahatchee, FL
Start seed indoors Not available Not available Not available –
Direct-sow outside Apr 8–Apr 22 Mar 10–Mar 24 Jan 27–Feb 10 –
Transplant outside Not available Not available Not available –
Fall planting Not available Not available Not available –
Expected harvest Jun 22–Aug 20 May 24–Jul 22 Apr 12–Jun 10 –

Zones 10-13 (hot, frost rare or absent) (Loxahatchee, FL): Frost is rare here (about 359 frost-free days a year); most years see little or no hard freeze. This is a hardy crop. In climates like this one, hardy and semi-hardy crops typically go in during the cooler months (fall through late winter), not on a frost-relative schedule.

Bulb onions go into the ground two to four weeks before your last frost, from seed or from sets. Colorado State University Extension's hardy-crop rule (Fact Sheet 7.212) states that window; Colorado State and Purdue Extension's soil-temperature tables (HO-186-W) agree exactly on a 35°F minimum, one of the coldest soil floors on this page and consistent with how hardy onion actually is.

Days to maturity for bulb onions run 75 to 120: NC State Extension's 75-to-105-day figure is from seed, and Colorado State's roughly 110 days and Missouri Extension's 100 to 120 land in a similar range from the same seed-or-sets convention. This figure is for bulb onion specifically; NC State gives a separate, much faster 42-to-56-day figure for green onion, a different crop use not folded into this row's range.

Because onion is hardy with a 35°F soil floor, a cold-winter climate can direct-seed or set out sets two to four weeks before frost without much risk; a mild-winter climate shifts the same window earlier and, depending on variety day-length requirements, may support a fall-planted crop as well.

Bulb onions are sold three ways at the nursery: seed, sets (small dormant bulbs planted directly), and occasionally transplants sold in bunches. Sets are the fastest and most forgiving route to a bulb harvest; seed takes the full 75-to-120-day range from the ground up.

Frost hardiness

Hardy. Tolerates hard frost. Can go in the ground before the last frost date.

Minimum soil temperature

35°F

For direct sowing/germination, where an Extension source stated it.

Days to maturity

75–120

Sourcing notes

From direct seed (sets/seed). CSU's hardy rule used. CSU and PURDUE Table 3 soil-temp minimums agree exactly at 35F. DTM convention differs: NCSU's 75-105 is from seed for bulb onions, CSU (~110) and MOEXT (100-120) roughly agree with each other for the seed/sets convention; combined range 75-120 reported, flagged. Green onion has a separate, faster NCSU figure (42-56 days) not included here since this row is for the bulb-onion crop.

Related crops

Growing zones for this crop

Nurseries near these locations

Sources