When to plant onions in Oklahoma
Oklahoma’s average last spring frost is April 1, and the first fall frost typically arrives around November 1 — about 214 frost-free days (USDA zones 6b, 7a, 7b, 8a). Onion needs 90–120 days to mature, which fits comfortably within Oklahoma's growing season.
When to plant onions in Oklahoma: the short answer
For a spring planting, plant out Mar 4 – Mar 21, with seeds started indoors Jan 14 – Jan 28. Seeds germinate in soil from 40 to 90°F.
Windows are ~1–2 week bands around each date. Frost dates are a statewide average from NOAA/NCEI normals; your town may differ by two weeks or more. Calendar year 2026.
How to grow onions in Oklahoma, step by step
- Start seeds indoors (Jan 14 – Jan 28). Sow seeds ½ inch deep in seed-starting mix under bright light. They take 7-14 days to sprout, fastest in soil around 70°F. Harden seedlings off for a week before they go outside.
- Prepare the bed. They need at least six to eight hours of direct sun a day and loose soil at least 12 inches deep, with a pH between 6.0 and 7.0. Dig in compost before planting.
- Plant out (Mar 4 – Mar 21). Space plants about 4 inches apart in rows 12 inches apart. It handles frost well, so it can go out before the last frost date. As a cool-season crop it does best before summer heat arrives in Oklahoma.
- Water and feed. Give it steady, even moisture, about an inch of water a week from rain or the hose.
- Watch for pests and problems. Pests: onion maggot, onion thrips. Diseases and disorders: downy mildew, white rot, neck rot, purple blotch.
- Harvest (from about Jun 9 – Jul 9). Onion takes 90-120 days to reach harvest. Match the day-length type to your latitude: long-day onions for the north, short-day for the south, day-neutral anywhere. Bulbing is triggered by day length, not calendar date.
Figures come from our crop data; dates use Oklahoma’s average frost dates. More in the full onion growing guide.
Onion planting dates by USDA zone in Oklahoma
Oklahoma spans USDA zones 6b, 7a, 7b, 8a. Colder zones, usually higher or further inland, have a later last spring frost and an earlier first fall frost than the state average, so the onion dates shift with them.
When to plant onions in nearby states
| State | Last frost | Plant out |
|---|---|---|
| Oklahoma (this page) | April 1 | Mar 4 – Mar 21 |
| North Dakota | May 15 | Apr 17 – May 4 |
| South Dakota | May 10 | Apr 12 – Apr 29 |
| Nebraska | April 30 | Apr 2 – Apr 19 |
| Kansas | April 15 | Mar 18 – Apr 4 |
Questions gardeners in Oklahoma ask
When is the best time to plant onions in Oklahoma?
Plant onion transplants outdoors in Oklahoma between March 4 and March 21. That timing is set by Oklahoma's average last spring frost of April 1.
When should I start onion seeds indoors in Oklahoma?
Start seeds indoors between January 14 and January 28, about 10 weeks before the last frost, so the seedlings are ready to plant out from March 4.
When will onions planted in Oklahoma be ready to harvest?
Planted on time, onions are usually ready from about June 9 to July 9, 90-120 days after transplanting.
When is the last frost in Oklahoma?
On average around April 1, with the first fall frost around November 1 - about 214 frost-free days. Your town may differ by two weeks or more.