What does USDA hardiness zone 4a mean in Utah?

Zone 4a means an average annual extreme minimum winter temperature of −30 to −25 °F — the standard USDA measure of which perennials survive winter. 1 location in Utah fall in this zone. It does not set planting dates; see the frost calendar below for that.

When should I plant tomatoes in Utah's zone 4a?

Using Randolph's frost dates (this page's median-season location): start seeds indoors about Apr 19 – May 3, then transplant outside about Jun 21 – Jun 28. 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 Utah's zone 4a 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 4a in Utah

−30 to −25 °F avg. annual extreme minimum · 1 location in this group · NOAA 1991–2020 normals

USDA plant hardiness zone 4a covers 1 location across Utah (average annual extreme minimum −30 to −25 °F): Randolph, UT. Average last spring frost across this group ranges June 14 and growing seasons run 76 days — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Utah location's own frost dates; the printable planting calendar uses Randolph, this group's median-season location.

USDA zone: 4a−30 to −25 °F
Last frost range: Jun 14avg, 32°F
First frost range: Sep 1avg, 32°F
Growing season range: 76days

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)
Randolph *	—	Randolph	Jun 14	Sep 1	76

* Randolph 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 (Randolph, representative)

Computed from Randolph's average frost dates — the median-season location in this Utahzone 4a 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 Randolph (Utah, zone 4a), this group's representative location.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting	Season fit
Tomato	Tender	Apr 19 – May 3	Jun 21 – Jun 28	Aug 20 – Sep 9	—	needs season extension (cold frame, row cover, or transplants) to mature
Pepper	Very tender	Apr 5 – Apr 19	Jun 28 – Jul 5	Aug 27 – Sep 26	—	needs season extension (cold frame, row cover, or transplants) to mature
Cucumber	Tender	May 17 – May 24	Jun 21 – Jun 28	Aug 10 – Aug 30	—	matures, but with little margin
Summer squash / zucchini	Tender	—	Jun 21 – Jun 28	Aug 5 – Aug 20	—	matures, but with little margin
Bush bean	Tender	—	Jun 21 – Jun 28	Aug 10 – Aug 20	Jul 3 – Jul 13	matures, but with little margin
Sweet corn	Tender	—	Jun 14 – Jun 28	Aug 13 – Sep 12	—	needs season extension (cold frame, row cover, or transplants) to mature
Basil	Very tender	May 3 – May 17	Jun 21 – Jun 28	Jul 21 – Aug 5	—	matures comfortably
Lettuce	Half-hardy	May 3 – May 17	May 17 – May 31	Jul 1 – Jul 16	Jun 19 – Jul 4	matures comfortably
Pea	Hardy	—	May 3 – May 17	Jun 27 – Jul 12	Jun 9 – Jun 24	matures comfortably
Spinach	Hardy	—	May 3 – May 17	Jun 12 – Jun 22	Jun 29 – Jul 9	matures comfortably
Carrot	Half-hardy	—	May 24 – May 31	Jul 23 – Aug 12	May 30 – Jun 19	matures comfortably
Broccoli	Half-hardy	Apr 19 – May 3	May 17 – May 31	Jul 11 – Jul 31	Jun 4 – Jun 24	matures comfortably

Which crops fit this growing season

Using Randolph's own 76-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 6 of 12 crops mature here with comfortable margin, 3mature with little room to spare, and 3 need season extension (starting indoors earlier, a cold frame, or row cover) to reliably reach harvest before the first fall frost. The tightest fits: tomato (-8 day margin), pepper (-25 day margin), cucumber (+2 day margin), summer squash / zucchini (+12 day margin), bush bean (+12 day margin), sweet corn (-11 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 (Randolph)

From NOAA's 1991–2020 Climate Normals at station USC00427165. 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), Randolph.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	—	—	—	—	48
32°F (freeze)	Jun 14	Jun 30	Sep 1	Sep 13	76
28°F	May 30	Jun 14	Sep 11	Sep 25	105
24°F	May 12	May 31	Sep 21	Oct 5	130

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 1,205; Randolph's own reading is shown below.

Annual growing degree days for Randolph (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	1,205	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	2,727	cool-season crops (brassicas, greens)

Hardiness zone 4a in Utah

Zone 4a means an average annual extreme minimum winter temperature of about −30 to −25 °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. Utah spans 9 hardiness zones in this dataset — see all Utah locations for the full range, including zones5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b.

Explore zone 4a in other states at zone 4a, or see all USDA hardiness zones.

Frequently asked questions

What does USDA hardiness zone 4a mean in Utah?: Zone 4a means an average annual extreme minimum winter temperature of −30 to −25 °F — the standard USDA measure of which perennials survive winter. 1 location in Utah fall in this zone. It does not set planting dates; see the frost calendar below for that.
When should I plant tomatoes in Utah's zone 4a?: Using Randolph's frost dates (this page's median-season location): start seeds indoors about Apr 19 – May 3, then transplant outside about Jun 21 – Jun 28. 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 Utah's zone 4a 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.