PlantAlong

When to plant peas in zone 9a

Transplant outdoors around Feb 3. That is 4 weeks before zone 9a's median last frost, Mar 21. Across most of zone 9a that date falls between Jan 19 and Feb 19.

Why a range: zone 9a is defined by winter lows, not frost dates. Its ZIP codes have median last frosts from Feb 16 to Mar 182, so a single zone date can be weeks off for you. The rule comes from Oregon State University Extension Service.

Last reviewed
Stations
432
ZIP codes
1,671
Photo: Mateusz Feliksik / 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
  4. Plant for fallTexas A&M (E-502)
  • 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. Peas in zone 9a. 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
Jan 68 weeks before last frost (Oregon State, central OR)
Transplant outdoors
Feb 3range Jan 19 – Feb 19
Fall planting
Sep 32-12 weeks before first frost

Five digits. The calendar is computed on your device.

What each source says, applied to zone 9a

The same frost dates give different answers depending on whose rule you follow. These are all the published rules we hold for peas, worked out at zone 9a's median frost dates.

Table 1. Peas rules from every source, at zone 9a's median last frost (Mar 2) and first frost (Nov 26).
SourceWhatRuleZone 9a median
Colorado State3Used aboveSow outdoors2-4 weeks before last frostFeb 3 – Feb 17
Oregon State, central OR1Used aboveTransplant outdoors4 weeks before last frostFeb 3
Oregon State, central OR1Used aboveStart indoors8 weeks before last frostJan 6
Texas A&M (E-502)4Sow outdoors2-8 weeks before last frostJan 6 – Feb 17
Texas A&M (E-502)4Used abovePlant for fall2-12 weeks before first frostSep 3 – Nov 12

Frost across zone 9a

  1. Last spring frostmedian Mar 2
  2. First fall frostmedian Nov 26
  • Frost-free season (median)
Figure 2. Frost dates across zone 9a, from 432 NOAA stations matched to 1,671 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. Texas AgriLife Extension Service, The Texas A&M System, Texas Home Vegetable Gardening Guide (E-502), 2/09. Retrieved 2026-11-02.