What does USDA hardiness zone 5b mean in California?

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 California fall in this zone. It does not set planting dates; see the frost calendar below for that.

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

Using Big Creek's frost dates (this page's median-season location): start seeds indoors about Jan 1 – Jan 12, then transplant outside about Mar 2 – Mar 9. 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 California'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 California

−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 California (average annual extreme minimum −15 to −10 °F): Big Creek, CA. Average last spring frost across this group ranges February 23 and growing seasons run 294 days — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every California location's own frost dates; the printable planting calendar uses Big Creek, this group's median-season location.

USDA zone: 5b−15 to −10 °F
Last frost range: Feb 23avg, 32°F
First frost range: Dec 12avg, 32°F
Growing season range: 294days

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)
Big Creek *	—	Balch Pwr House	Feb 23	Dec 12	294

* Big Creek 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 (Big Creek, representative)

Computed from Big Creek's average frost dates — the median-season location in this Californiazone 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 Big Creek (California, zone 5b), this group's representative location.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting	Season fit
Tomato	Tender	Jan 1 – Jan 12	Mar 2 – Mar 9	May 1 – May 21	—	matures comfortably
Pepper	Very tender	Jan 1	Mar 9 – Mar 16	May 8 – Jun 7	—	matures comfortably
Cucumber	Tender	Jan 26 – Feb 2	Mar 2 – Mar 9	Apr 21 – May 11	—	matures comfortably
Summer squash / zucchini	Tender	—	Mar 2 – Mar 9	Apr 16 – May 1	—	matures comfortably
Bush bean	Tender	—	Mar 2 – Mar 9	Apr 21 – May 1	Oct 13 – Oct 23	matures comfortably
Sweet corn	Tender	—	Feb 23 – Mar 9	Apr 24 – May 24	—	matures comfortably
Basil	Very tender	Jan 12 – Jan 26	Mar 2 – Mar 9	Apr 1 – Apr 16	—	matures comfortably
Lettuce	Half-hardy	Jan 12 – Jan 26	Jan 26 – Feb 9	Mar 12 – Mar 27	Sep 29 – Oct 14	matures comfortably
Pea	Hardy	—	Jan 12 – Jan 26	Mar 8 – Mar 23	Sep 19 – Oct 4	matures comfortably
Spinach	Hardy	—	Jan 12 – Jan 26	Feb 21 – Mar 3	Oct 9 – Oct 19	matures comfortably
Carrot	Half-hardy	—	Feb 2 – Feb 9	Apr 3 – Apr 23	Sep 9 – Sep 29	matures comfortably
Broccoli	Half-hardy	Jan 1 – Jan 12	Jan 26 – Feb 9	Mar 22 – Apr 11	Sep 14 – Oct 4	matures comfortably

Which crops fit this growing season

Using Big Creek's own 294-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable 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 (Big Creek)

From NOAA's 1991–2020 Climate Normals at station USC00040449. 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), Big Creek.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	Apr 2	Apr 24	Nov 27	Dec 12	240
32°F (freeze)	Feb 23	Apr 4	Dec 12	Jan 7	294
28°F	Jan 21	Mar 3	Dec 27	Feb 11	351
24°F	Dec 31	Jan 29	Dec 29	Jan 28	365

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 4,923; Big Creek's own reading is shown below.

Annual growing degree days for Big Creek (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	4,923	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	8,069	cool-season crops (brassicas, greens)

Hardiness zone 5b in California

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. California spans 12 hardiness zones in this dataset — see all California locations for the full range, including zones6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b, 10a, 10b, 11a.

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 California?: 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 California fall in this zone. It does not set planting dates; see the frost calendar below for that.
When should I plant tomatoes in California's zone 5b?: Using Big Creek's frost dates (this page's median-season location): start seeds indoors about Jan 1 – Jan 12, then transplant outside about Mar 2 – Mar 9. 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 California'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.