When to plant zucchini in zone 9a

Transplant outdoors around Mar 16. That is 2 weeks after zone 9a's median last frost, Mar 21. Across most of zone 9a that date falls between Mar 1 and Apr 1.

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: 2026-11-02
Stations: 432
ZIP codes: 1,671

Photo: Gu Bra / Pexels

These dates use the typical last frost for the whole zone. Your ZIP code gives a closer answer.

Start indoorsOregon State, central ORStart indoors across most of the zone: Feb 9 to Mar 11Start indoors at the zone median: Feb 24 (Oregon State, central OR)
Transplant outdoorsOregon State, central ORTransplant outdoors across most of the zone: Mar 1 to Apr 1Transplant outdoors at the zone median: Mar 16 (Oregon State, central OR)
Sow outdoorsColorado StateSow outdoors across most of the zone: Feb 16 to Mar 18Sow outdoors at the zone median: Mar 2 (Colorado State)
Plant for fallTexas A&M (E-502)Plant for fall across most of the zone: Aug 3 to Sep 16Plant for fall at the zone median: Aug 13 to Sep 3 (Texas 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. Zucchini 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: Feb 241 weeks before last frost (Oregon State, central OR)
Transplant outdoors: Mar 16range Mar 1 – Apr 1
Fall planting: Aug 1312-15 weeks before first frost

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 zucchini, worked out at zone 9a's median frost dates.

Table 1. Zucchini rules from every source, at zone 9a's median last frost (Mar 2) and first frost (Nov 26).
Source	What	Rule	Zone 9a median
Colorado State3Used above	Sow outdoors	On the last frost	Mar 2
Utah State4	Sow outdoors	On the last frost	Mar 2
Oregon State, central OR1Used above	Transplant outdoors	2 weeks after last frost	Mar 16
Oregon State, central OR1Used above	Start indoors	1 weeks before last frost	Feb 24
Texas A&M (E-502)5	Sow outdoors	1-4 weeks after last frost	Mar 9 – Mar 30
Texas A&M (E-502)5Used above	Plant for fall	12-15 weeks before first frost	Aug 13 – Sep 3

Frost across zone 9a

Last spring frostmedian Mar 2Full range across the zone: Jan 6 to Jun 3Most of the zone (10th to 90th percentile): Feb 16 to Mar 18Zone median: Mar 2
First fall frostmedian Nov 26Full range across the zone: Sep 14 to Feb 1Most of the zone (10th to 90th percentile): Nov 16 to Dec 9Zone median: Nov 26

Frost-free season (median)

Figure 2. Frost dates across zone 9a, from 432 NOAA stations matched to 1,671 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.6 7 7 8 8
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.9 9 9 10 10 9

Sources

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