What USDA hardiness zone is Elk River?

Elk River, Idaho is in USDA plant hardiness zone 6b on the 2023 map (average annual extreme minimum temperature −5 to 0 °F) — from the USDA Plant Hardiness Zone Map 2023, matched to this location's ZIP. See the methodology page for sources.

When is the last frost in Elk River?

The average (median) last spring frost at 32°F is around May 16, from NOAA's 1991–2020 climate normals at the nearest reporting station. Roughly one year in ten the last frost is as late as June 1, so wait until then before setting out frost-tender plants if you want to be safe.

When is the first fall frost in Elk River?

The average first fall frost at 32°F is around September 23. That leaves a growing season of about 128 days between the average last spring and first fall frosts.

When should I start tomatoes in Elk River?

Start tomato seeds indoors about Mar 21 – Apr 4 and transplant them outside about May 23 – May 30, once the danger of frost has passed. Estimated first harvest is around Jul 22 – Aug 11.

How long is the growing season in Elk River?

About 128 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~May 16) and the average first fall frost (~September 23). Cold-hardy crops extend usable time at both ends; frost-tender crops fit inside it.

Elk River, ID planting calendar

USDA hardiness zone 6b · nearest station Elk Rvr (0.6 km) · NOAA 1991–2020 normals

USDA zone: 6b−5 to 0 °F
Last frost: May 16avg, 32°F
First frost: Sep 23avg, 32°F
Growing season: 128days

Elk River, Idaho is in USDA plant hardiness zone 6b. Its average last spring frost is around May 16 and the first fall frost around September 23, giving a growing season of about 128 days (NOAA 1991–2020 normals, 32°F, median). Start tender crops like tomatoes and peppers indoors weeks before the last frost and set them out afterward; sow hardy crops such as peas, spinach, and lettuce before it. The planner below turns those frost dates into a printable per-crop planting calendar.

Elk River planting calendar

Each crop's windows are counted from Elk River's average frost dates. 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.

Crop

JanFebMarAprMayJunJulAugSepOctNovDec

Tomato

Pepper

Cucumber

Summer squash / zucchini

Bush bean

Sweet corn

Basil

Lettuce

Pea

Spinach

Carrot

Broccoli

Start indoors
Plant out
Fall sowing
First harvest

Planting windows for Elk River. Dates are planning ranges from U.S. Cooperative Extension guides.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting
Tomato	Tender	Mar 21 – Apr 4	May 23 – May 30	Jul 22 – Aug 11	—
Pepper	Very tender	Mar 7 – Mar 21	May 30 – Jun 6	Jul 29 – Aug 28	—
Cucumber	Tender	Apr 18 – Apr 25	May 23 – May 30	Jul 12 – Aug 1	—
Summer squash / zucchini	Tender	—	May 23 – May 30	Jul 7 – Jul 22	—
Bush bean	Tender	—	May 23 – May 30	Jul 12 – Jul 22	Jul 25 – Aug 4
Sweet corn	Tender	—	May 16 – May 30	Jul 15 – Aug 14	—
Basil	Very tender	Apr 4 – Apr 18	May 23 – May 30	Jun 22 – Jul 7	—
Lettuce	Half-hardy	Apr 4 – Apr 18	Apr 18 – May 2	Jun 2 – Jun 17	Jul 11 – Jul 26
Pea	Hardy	—	Apr 4 – Apr 18	May 29 – Jun 13	Jul 1 – Jul 16
Spinach	Hardy	—	Apr 4 – Apr 18	May 14 – May 24	Jul 21 – Jul 31
Carrot	Half-hardy	—	Apr 25 – May 2	Jun 24 – Jul 14	Jun 21 – Jul 11
Broccoli	Half-hardy	Mar 21 – Apr 4	Apr 18 – May 2	Jun 12 – Jul 2	Jun 26 – Jul 16

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.

Frost & freeze dates

From NOAA's 1991–2020 Climate Normals at station USC00102892. 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 (p10 for spring, p90 for fall) — the conservative date to plant after or harvest before.

Freeze probabilities by temperature threshold (MM/DD, NOAA 1991–2020).
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	Jun 6	Jul 6	Sep 10	Sep 25	92
32°F (freeze)	May 16	Jun 1	Sep 23	Oct 9	128
28°F	Apr 30	May 14	Oct 8	Oct 29	160
24°F	Apr 7	Apr 27	Oct 29	Nov 20	203

32°F is the standard "freeze" line that damages tender crops; lighter 36°F frost can nip the most cold-sensitive plants, while hardy crops shrug off light frost down toward 28°F. Use the threshold that matches what you are protecting.

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. Warm-season crops need a long, warm GDD total; a short, cool GDD total favors greens and brassicas.

Annual growing degree days for Elk River (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	1,556	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	3,264	cool-season crops (brassicas, greens)

Hardiness zone 6b

Elk River sits in USDA plant hardiness zone 6b on the 2023 map — meaning its average annual extreme minimum winter temperature is about −5 to 0 °F. That number 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.

Explore more places in zone 6b, or see all USDA hardiness zones.

Frequently asked questions

What USDA hardiness zone is Elk River?: Elk River, Idaho is in USDA plant hardiness zone 6b on the 2023 map (average annual extreme minimum temperature −5 to 0 °F) — from the USDA Plant Hardiness Zone Map 2023, matched to this location's ZIP. See the methodology page for sources.
When is the last frost in Elk River?: The average (median) last spring frost at 32°F is around May 16, from NOAA's 1991–2020 climate normals at the nearest reporting station. Roughly one year in ten the last frost is as late as June 1, so wait until then before setting out frost-tender plants if you want to be safe.
When is the first fall frost in Elk River?: The average first fall frost at 32°F is around September 23. That leaves a growing season of about 128 days between the average last spring and first fall frosts.
When should I start tomatoes in Elk River?: Start tomato seeds indoors about Mar 21 – Apr 4 and transplant them outside about May 23 – May 30, once the danger of frost has passed. Estimated first harvest is around Jul 22 – Aug 11.
How long is the growing season in Elk River?: About 128 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~May 16) and the average first fall frost (~September 23). Cold-hardy crops extend usable time at both ends; frost-tender crops fit inside it.

Sources & method

Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020 for station USC00102892 (Elk Rvr, 0.6 km away). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to this 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.