PlantAlong

When to plant zucchini in zone 6b

Transplant outdoors around May 6. That is 2 weeks after zone 6b's median last frost, Apr 221. Across most of zone 6b that date falls between Apr 24 and May 17.

Why a range: zone 6b is defined by winter lows, not frost dates. Its ZIP codes have median last frosts from Apr 10 to May 32, so a single zone date can be weeks off for you. The rule comes from Oregon State University Extension Service.

Last reviewed
Stations
899
ZIP codes
4,372
Photo: Gu Bra / 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. Zucchini in zone 6b. 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
Apr 151 weeks before last frost (Oregon State, central OR)
Transplant outdoors
May 6range Apr 24 – May 17

Five digits. The calendar is computed on your device.

What each source says, applied to zone 6b

The same frost dates give different answers depending on whose rule you follow. These are all the published rules we hold for zucchini, worked out at zone 6b's median frost dates.

Table 1. Zucchini rules from every source, at zone 6b's median last frost (Apr 22) and first frost (Oct 22).
SourceWhatRuleZone 6b median
Colorado State3Used aboveSow outdoorsOn the last frostApr 22
Utah State4Sow outdoorsOn the last frostApr 22
Oregon State, central OR1Used aboveTransplant outdoors2 weeks after last frostMay 6
Oregon State, central OR1Used aboveStart indoors1 weeks before last frostApr 15
Texas A&M (E-502)5Sow outdoors1-4 weeks after last frostApr 29 – May 20
Texas A&M (E-502)5Plant for fall12-15 weeks before first frostJul 9 – Jul 30

Frost across zone 6b

  1. Last spring frostmedian Apr 22
  2. First fall frostmedian Oct 22
  • Frost-free season (median)
Figure 2. Frost dates across zone 6b, from 899 NOAA stations matched to 4,372 ZIP codes.

Planting zucchini with others

  • Marigold Tested in a study Tradition lists marigold as a squash companion (no reason given). Field tests of squash (Cucurbita pepo) intercropped with French marigold found no consistent nematode effect.67788
  • Blue Hubbard squash Tested in a study A border of Blue Hubbard squash draws striped cucumber beetles away from the summer squash it encircles; the border is sprayed when beetles arrive.99910109

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.
  6. University of California Agriculture and Natural Resources (UCCE Master Gardener Program), Companion Planting Chart: Companion planting in the vegetable garden, File dated 2023-09 in URL path; no date printed. Retrieved 2026-11-02.
  7. Journal of Nematology 25(4):666-673 (Society of Nematologists); FLVC journal host, Effects of Mixed Cropping on a Soil Nematode Community in Honduras, 1993. Retrieved 2026-11-02.
  8. University of Florida, IFAS Extension (Entomology and Nematology Department), Marigolds (Tagetes spp.) for Nematode Management (ENY-056), reviewed Reviewed November 2019; page footer "Reviewed: 01/2024". Retrieved 2026-11-02.
  9. University of Vermont Extension, Vermont Vegetable and Berry Program, Perimeter Trap Cropping: A Novel Approach to Insect Pest Control, July 2004. Retrieved 2026-11-02.
  10. Journal of Extension 42(5), Article 13, Demonstrating a Perimeter Trap Crop Approach to Pest Management on Summer Squash in New England, October 2004. Retrieved 2026-11-02.