USDA zone 6b in Oklahoma
USDA plant hardiness zone 6b covers 6 locations across Oklahoma (average annual extreme minimum −5 to 0 °F): Beaver, OK, Boise, OK, Guymon, OK, Hooker, OK, Kenton, OK, North Miami, OK. Average last spring frost across this group ranges April 6 (North Miami) to April 29 (Kenton), and growing seasons run 166–203 days (Kenton to North Miami) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Oklahoma location's own frost dates; the printable planting calendar uses Guymon, this group's median-season location.
- USDA zone
- 6b−5 to 0 °F
- Last frost range
- Apr 6–Apr 29avg, 32°F
- First frost range
- Oct 13–Oct 27avg, 32°F
- Growing season range
- 166–203days
Locations in this group
Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.
| Location | Also covers | Nearest station | Last frost | First frost | Season (days) |
|---|---|---|---|---|---|
| Beaver | Forgan | Beaver | Apr 21 | Oct 21 | 181 |
| Boise | Felt | Boise City 2 E | Apr 26 | Oct 17 | 173 |
| Guymon * | — | Guymon Muni Ap | Apr 18 | Oct 23 | 188 |
| Hooker | Adams, Hardesty | Hooker | Apr 16 | Oct 25 | 192 |
| Kenton | Campo | Campo 7 S | Apr 29 | Oct 13 | 166 |
| North Miami | — | Miami | Apr 6 | Oct 27 | 203 |
* Guymon is this group's median-season location — the calendar below is computed from its data.
Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.
Planting calendar (Guymon, representative)
Computed from Guymon's average frost dates — the median-season location in this Oklahomazone 6b group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting | Season fit |
|---|---|---|---|---|---|---|
| Tomato | Tender | Feb 21 – Mar 7 | Apr 25 – May 2 | Jun 24 – Jul 14 | — | matures comfortably |
| Pepper | Very tender | Feb 7 – Feb 21 | May 2 – May 9 | Jul 1 – Jul 31 | — | matures comfortably |
| Cucumber | Tender | Mar 21 – Mar 28 | Apr 25 – May 2 | Jun 14 – Jul 4 | — | matures comfortably |
| Summer squash / zucchini | Tender | — | Apr 25 – May 2 | Jun 9 – Jun 24 | — | matures comfortably |
| Bush bean | Tender | — | Apr 25 – May 2 | Jun 14 – Jun 24 | Aug 24 – Sep 3 | matures comfortably |
| Sweet corn | Tender | — | Apr 18 – May 2 | Jun 17 – Jul 17 | — | matures comfortably |
| Basil | Very tender | Mar 7 – Mar 21 | Apr 25 – May 2 | May 25 – Jun 9 | — | matures comfortably |
| Lettuce | Half-hardy | Mar 7 – Mar 21 | Mar 21 – Apr 4 | May 5 – May 20 | Aug 10 – Aug 25 | matures comfortably |
| Pea | Hardy | — | Mar 7 – Mar 21 | May 1 – May 16 | Jul 31 – Aug 15 | matures comfortably |
| Spinach | Hardy | — | Mar 7 – Mar 21 | Apr 16 – Apr 26 | Aug 20 – Aug 30 | matures comfortably |
| Carrot | Half-hardy | — | Mar 28 – Apr 4 | May 27 – Jun 16 | Jul 21 – Aug 10 | matures comfortably |
| Broccoli | Half-hardy | Feb 21 – Mar 7 | Mar 21 – Apr 4 | May 15 – Jun 4 | Jul 26 – Aug 15 | matures comfortably |
Which crops fit this growing season
Using Guymon's own 188-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.
Frost & freeze dates (Guymon)
From NOAA's 1991–2020 Climate Normals at station USW00003030. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.
| Threshold | Last spring — avg | Last spring — 90%-safe | First fall — avg | First fall — 90%-safe | Season (days) |
|---|---|---|---|---|---|
| 36°F | Apr 28 | May 10 | Oct 14 | Oct 26 | 169 |
| 32°F (freeze) | Apr 18 | May 1 | Oct 23 | Nov 3 | 188 |
| 28°F | Apr 8 | Apr 23 | Nov 1 | Nov 12 | 206 |
| 24°F | Mar 29 | Apr 14 | Nov 8 | Nov 22 | 225 |
Growing degree days
Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 6 locations is 4,367; Guymon's own reading is shown below.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 4,437 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 7,059 | cool-season crops (brassicas, greens) |
Hardiness zone 6b in Oklahoma
Zone 6b means an average annual extreme minimum winter temperature of about −5 to 0 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Oklahoma spans 4 hardiness zones in this dataset — see all Oklahoma locations for the full range, including zones7a, 7b, 8a.
Explore zone 6b in other states at zone 6b, or see all USDA hardiness zones.
Frequently asked questions
- What does USDA hardiness zone 6b mean in Oklahoma?
- Zone 6b means an average annual extreme minimum winter temperature of −5 to 0 °F — the standard USDA measure of which perennials survive winter. 6 locations in Oklahoma fall in this zone. It does not set planting dates; see the frost calendar below for that.
- Where in Oklahoma's zone 6b is the growing season longest?
- North Miami runs the longest season on this page at about 203 days; Kenton is shortest at about 166 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
- When should I plant tomatoes in Oklahoma's zone 6b?
- Using Guymon's frost dates (this page's median-season location): start seeds indoors about Feb 21 – Mar 7, then transplant outside about Apr 25 – May 2. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
- Does every location in Oklahoma's zone 6b have the same frost dates?
- No — they do not all share a weather station, so frost dates vary by a week or more across the 6 locations listed (see the table above for each location's own dates).
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.