PlantAlong

When to plant beans in zone 8b

Transplant outdoors around Mar 24. That is 1 weeks after zone 8b's median last frost, Mar 171. Across most of zone 8b that date falls between Mar 13 and Apr 8.

Why a range: zone 8b is defined by winter lows, not frost dates. Its ZIP codes have median last frosts from Mar 6 to Apr 12, so a single zone date can be weeks off for you. The rule comes from Oregon State University Extension Service.

Last reviewed
Stations
652
ZIP codes
2,535
Photo: Gobral / Pexels
These dates use the typical last frost for the whole zone. Your ZIP code gives a closer answer.
  1. Start indoorsOregon State, central OR
  2. Transplant outdoorsOregon State, central OR
  3. Sow outdoorsColorado State
  • Start indoors
  • Plant outdoors
  • Range across the zone
  • Frost-free season (median)
  • Spring frost risk (90% to 10%)
  • Fall frost risk (10% to 90%)
Figure 1. Beans in zone 8b. Dark bars: at the zone's median frost dates. Pale bars: across most of the zone's ZIP codes. Hatched blue: where the zone's last and first frosts fall.
Start seeds indoors
Feb 253 weeks before last frost (Oregon State, central OR)
Transplant outdoors
Mar 24range Mar 13 – Apr 8

Five digits. The calendar is computed on your device.

What each source says, applied to zone 8b

The same frost dates give different answers depending on whose rule you follow. These are all the published rules we hold for beans, worked out at zone 8b's median frost dates.

Table 1. Beans rules from every source, at zone 8b's median last frost (Mar 17) and first frost (Nov 13).
SourceWhatRuleZone 8b median
Colorado State3Used aboveSow outdoorsOn the last frostMar 17
Utah State4Sow outdoorsOn the last frostMar 17
Oregon State, central OR1Used aboveTransplant outdoors1 weeks after last frostMar 24
Oregon State, central OR1Used aboveStart indoors3 weeks before last frostFeb 25
Texas A&M (E-502)5Sow outdoors1-4 weeks after last frostMar 24 – Apr 14
Texas A&M (E-502)5Plant for fall8-10 weeks before first frostSep 4 – Sep 18
Texas A&M (E-502)5Plant for fall14-16 weeks before first frostJul 24 – Aug 7

Frost across zone 8b

  1. Last spring frostmedian Mar 17
  2. First fall frostmedian Nov 13
  • Frost-free season (median)
Figure 2. Frost dates across zone 8b, from 652 NOAA stations matched to 2,535 ZIP codes.

Sources

  1. Oregon State University Extension Service, When to start seeds indoors in central Oregon, reviewed 2024. Retrieved 2026-11-02.
  2. NOAA National Centers for Environmental Information, U.S. Climate Normals 2020: U.S. Annual/Seasonal Climate Normals (1991-2020), 2021. Retrieved 2026-11-02.
  3. Colorado State University Extension, Vegetable Planting Guide (CMG GardenNotes #720), reviewed September 2024. Retrieved 2026-11-02.
  4. Utah State University Extension, Suggested Vegetable Planting Dates for Utah, January 2018; revised May 2025. Retrieved 2026-11-02.
  5. Texas AgriLife Extension Service, The Texas A&M System, Texas Home Vegetable Gardening Guide (E-502), 2/09. Retrieved 2026-11-02.