What does USDA hardiness zone 5b mean in Oregon?

Zone 5b means an average annual extreme minimum winter temperature of −15 to −10 °F — the standard USDA measure of which perennials survive winter. 1 location in Oregon fall in this zone. It does not set planting dates; see the frost calendar below for that.

When should I plant tomatoes in Oregon's zone 5b?

Using Seneca's frost dates (this page's median-season location): start seeds indoors about Apr 2 – Apr 16, then transplant outside about Jun 4 – Jun 11. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.

Does every location in Oregon's zone 5b have the same frost dates?

No — they do not all share a weather station, so frost dates vary by a week or more across the 1 locations listed (see the table above for each location's own dates).

USDA zone 5b in Oregon

−15 to −10 °F avg. annual extreme minimum · 1 location in this group · NOAA 1991–2020 normals

USDA plant hardiness zone 5b covers 1 location across Oregon (average annual extreme minimum −15 to −10 °F): Seneca, OR. Average last spring frost across this group ranges May 28 and growing seasons run 113 days — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Oregon location's own frost dates; the printable planting calendar uses Seneca, this group's median-season location.

USDA zone: 5b−15 to −10 °F
Last frost range: May 28avg, 32°F
First frost range: Sep 18avg, 32°F
Growing season range: 113days

Locations in this group

Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.

Own frost dates per location.
Location	Also covers	Nearest station	Last frost	First frost	Season (days)
Seneca *	—	John Day	May 28	Sep 18	113

* Seneca is this group's median-season location — the calendar below is computed from its data.

Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.

Planting calendar (Seneca, representative)

Computed from Seneca's average frost dates — the median-season location in this Oregonzone 5b group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).

Crop

JanFebMarAprMayJunJulAugSepOctNovDec

Tomato

Pepper

Cucumber

Summer squash / zucchini

Start indoors
Plant out
Fall sowing
First harvest

Planting windows for Seneca (Oregon, zone 5b), this group's representative location.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting	Season fit
Tomato	Tender	Apr 2 – Apr 16	Jun 4 – Jun 11	Aug 3 – Aug 23	—	matures comfortably
Pepper	Very tender	Mar 19 – Apr 2	Jun 11 – Jun 18	Aug 10 – Sep 9	—	matures, but with little margin
Cucumber	Tender	Apr 30 – May 7	Jun 4 – Jun 11	Jul 24 – Aug 13	—	matures comfortably
Summer squash / zucchini	Tender	—	Jun 4 – Jun 11	Jul 19 – Aug 3	—	matures comfortably
Bush bean	Tender	—	Jun 4 – Jun 11	Jul 24 – Aug 3	Jul 20 – Jul 30	matures comfortably
Sweet corn	Tender	—	May 28 – Jun 11	Jul 27 – Aug 26	—	matures comfortably
Basil	Very tender	Apr 16 – Apr 30	Jun 4 – Jun 11	Jul 4 – Jul 19	—	matures comfortably
Lettuce	Half-hardy	Apr 16 – Apr 30	Apr 30 – May 14	Jun 14 – Jun 29	Jul 6 – Jul 21	matures comfortably
Pea	Hardy	—	Apr 16 – Apr 30	Jun 10 – Jun 25	Jun 26 – Jul 11	matures comfortably
Spinach	Hardy	—	Apr 16 – Apr 30	May 26 – Jun 5	Jul 16 – Jul 26	matures comfortably
Carrot	Half-hardy	—	May 7 – May 14	Jul 6 – Jul 26	Jun 16 – Jul 6	matures comfortably
Broccoli	Half-hardy	Apr 2 – Apr 16	Apr 30 – May 14	Jun 24 – Jul 14	Jun 21 – Jul 11	matures comfortably

Which crops fit this growing season

Using Seneca's own 113-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 11 of 12 crops mature here with comfortable margin, 1matures with little room to spare. The tightest fits: pepper (+9 day margin). A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.

Frost & freeze dates (Seneca)

From NOAA's 1991–2020 Climate Normals at station USC00354291. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.

Freeze probabilities by temperature threshold (MM/DD, NOAA 1991–2020), Seneca.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	Jun 19	Jul 8	Sep 2	Sep 20	76
32°F (freeze)	May 28	Jun 15	Sep 18	Oct 4	113
28°F	May 8	May 24	Oct 1	Oct 16	146
24°F	Apr 23	May 7	Oct 13	Nov 2	175

Growing degree days

Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 1 locations is 1,760; Seneca's own reading is shown below.

Annual growing degree days for Seneca (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	1,760	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	3,642	cool-season crops (brassicas, greens)

Hardiness zone 5b in Oregon

Zone 5b means an average annual extreme minimum winter temperature of about −15 to −10 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Oregon spans 9 hardiness zones in this dataset — see all Oregon locations for the full range, including zones6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b.

Explore zone 5b in other states at zone 5b, or see all USDA hardiness zones.

Frequently asked questions

What does USDA hardiness zone 5b mean in Oregon?: Zone 5b means an average annual extreme minimum winter temperature of −15 to −10 °F — the standard USDA measure of which perennials survive winter. 1 location in Oregon fall in this zone. It does not set planting dates; see the frost calendar below for that.
When should I plant tomatoes in Oregon's zone 5b?: Using Seneca's frost dates (this page's median-season location): start seeds indoors about Apr 2 – Apr 16, then transplant outside about Jun 4 – Jun 11. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
Does every location in Oregon's zone 5b have the same frost dates?: No — they do not all share a weather station, so frost dates vary by a week or more across the 1 locations listed (see the table above for each location's own dates).

Sources & method

Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.