When to plant cucumbers in zone 4a

Transplant outdoors around May 19. That is 1 weeks after zone 4a's median last frost, May 121. Across most of zone 4a that date falls between May 12 and May 31.

Why a range: zone 4a is defined by winter lows, not frost dates. Its ZIP codes have median last frosts from May 5 to May 242, 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: 276
ZIP codes: 720

Photo: Agung Sutrisno / 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: Apr 21 to May 10Start indoors at the zone median: Apr 28 (Oregon State, central OR)
Transplant outdoorsOregon State, central ORTransplant outdoors across most of the zone: May 12 to May 31Transplant outdoors at the zone median: May 19 (Oregon State, central OR)
Sow outdoorsColorado StateSow outdoors across most of the zone: May 5 to May 24Sow outdoors at the zone median: May 12 (Colorado 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. Cucumbers in zone 4a. 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 282 weeks before last frost (Oregon State, central OR)
Transplant outdoors: May 19range May 12 – May 31

What each source says, applied to zone 4a

The same frost dates give different answers depending on whose rule you follow. These are all the published rules we hold for cucumbers, worked out at zone 4a's median frost dates.

Table 1. Cucumbers rules from every source, at zone 4a's median last frost (May 12) and first frost (Sep 28).
Source	What	Rule	Zone 4a median
Colorado State3Used above	Sow outdoors	On the last frost	May 12
Utah State4	Sow outdoors	On the last frost	May 12
Oregon State, central OR1Used above	Transplant outdoors	1 weeks after last frost	May 19
Oregon State, central OR1Used above	Start indoors	2 weeks before last frost	Apr 28
Texas A&M (E-502)5	Sow outdoors	1-6 weeks after last frost	May 19 – Jun 23
Texas A&M (E-502)5	Plant for fall	10-12 weeks before first frost	Jul 6 – Jul 20

Frost across zone 4a

Last spring frostmedian May 12Full range across the zone: May 2 to Jun 14Most of the zone (10th to 90th percentile): May 5 to May 24Zone median: May 12
First fall frostmedian Sep 28Full range across the zone: Sep 1 to Oct 9Most of the zone (10th to 90th percentile): Sep 20 to Oct 4Zone median: Sep 28

Frost-free season (median)

Figure 2. Frost dates across zone 4a, from 276 NOAA stations matched to 720 ZIP codes.

Planting cucumbers with others

Marigold Tested in a study Claimed: marigold root exudates suppress nematodes. Field tests intercropping cucumber and squash with French marigold found no consistent effect on soil nematodes.6 6 6 7 7
Blue Hubbard squash Tested in a study A border of Blue Hubbard squash, which striped cucumber beetles prefer, encircles the cucumbers; beetles concentrate on the border, which is then sprayed.8 8 8 9 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.
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 Connecticut Cooperative Extension System (UConn IPM), Protecting Cucumbers From Beetles and Wilt With Perimeter Trap Cropping, reviewed Reviewed 2012. 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.