Oklahoma planting calendar

When to plant onions in Oklahoma — sow, transplant & harvest dates

Oklahoma is mostly USDA zone 7b (range 6b-8a). Dates below are derived from onions's frost tolerance and Oklahoma's frost window — not generic national averages.

Onions planting timetable for Oklahoma

Stage	When in Oklahoma	Anchor
Start seeds indoors	late January (January 25)	10 weeks before the last frost (early April)
Transplant outside	early March (March 8)	28 days before the last frost (early April)
First harvest (estimate)	late June (June 26)	~110 days from transplant

Dates are state-wide averages for the dominant zone. Local microclimates — elevation, urban heat, coastal moderation — can shift the window by 1-2 weeks. Use the frost-date calculator for a date tuned to your town.

Why Oklahoma's climate shifts the onions dates

Oklahoma's last spring frost averages early April and first fall frost late October, which sets the whole planting clock. Oklahoma has a long, hot, often windy season. Summer heat and drought stress are as limiting as the winter low across most of the state. Sow early — onions bolt once daytime temperatures hold above 24 °C, so the earlier they go in, the longer the harvest.

Onions are day-length sensitive: long-day varieties (zones 1–6) begin bulbing when days exceed 14 hours, short-day types (zones 7–10) bulb at 10–12 hours, and intermediate-day varieties span zones 5–6. Start seeds indoors 10–12 weeks before the last spring frost and transplant out 4–6 weeks before it — young onion seedlings tolerate frost down to about -6 °C once hardened off. In zones 8–10 a second planting from sets in autumn is common, overwintering for an early-summer harvest.

Frost-risk note

Don't plant before early April — a hard freeze can still set young plants back. In the Panhandle High Plains (zone 6b) the safe date runs a week or two later.

Regional variation within Oklahoma

the Panhandle High Plains (zone 6b) runs roughly 1-2 weeks behind the state average; the south-central and southeast lowlands (zone 8a) can plant 1-2 weeks earlier.

Oklahoma City — USDA zone 7b
Tulsa — USDA zone 7b
Norman — USDA zone 7b
Lawton — USDA zone 8a

What else to plant in Oklahoma around then

The same early window suits peas, lettuce, spinach, and onion sets.

Quick-grow guide

Sun: Full sun — 6+ hours direct.
Soil temperature for germination: 10-35 °C (50-95 °F).
Spacing: 4-6 inches (10-15 cm) between plants.
Days to harvest: ~110 days from planting out.

Frequently asked questions

When is the best time to plant onions in Oklahoma?

In Oklahoma (mostly USDA zone 7b), sow onions indoors around late January, transplant outdoors early March (before the last frost, early April), and harvest from late June. Onions are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

What USDA zone is Oklahoma?

Most of Oklahoma sits in USDA hardiness zone 7b, with the state spanning roughly 6b-8a from the Panhandle High Plains (zone 6b) to the south-central and southeast lowlands (zone 8a). The last spring frost averages early April and the first fall frost late October.

Can you grow onions in Oklahoma?

Yes. Oklahoma's dominant zone 7b supports onions — the key is timing. Onions are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

Does the planting date change across Oklahoma?

the Panhandle High Plains (zone 6b) runs roughly 1-2 weeks behind the state average; the south-central and southeast lowlands (zone 8a) can plant 1-2 weeks earlier.

What else can I plant in Oklahoma around the same time?

The same early window suits peas, lettuce, spinach, and onion sets.

Source and methodology

State zone spans from the USDA Plant Hardiness Zone Map (2023); frost-date averages from NOAA Climate Data Online. Hot-state two-season timing cross-checked against the UF/IFAS Florida Gardening Calendar and the University of Arizona Cooperative Extension planting calendar. Curated by the Growli editorial team.