Rock Springs, WY planting zone & frost dates

Rock Springs is in USDA hardiness zone 5a. The last spring frost usually comes around May 24 and the first fall frost around September 24, for a growing season of about 121 days.

USDA hardiness zone5aavg. extreme winter low -20°F to -15°F

Average last spring frostMay 2490% chance of no frost after June 9

Average first fall frostSeptember 2410% chance of frost by September 9

Growing season121 daysfrost-free days in an average year

Planting calendar for Rock Springs

Dates are counted from the average last spring frost (May 24) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.

Crop	When
Tomatoes	Start seeds indoors: Mar 29 – Apr 12 Transplant outdoors: May 31 – Jun 7
Peppers	Start seeds indoors: Mar 15 – Mar 29 Transplant outdoors: Jun 7 – Jun 14
Eggplant	Start seeds indoors: Mar 15 – Mar 29 Transplant outdoors: Jun 7 – Jun 14
Broccoli	Start seeds indoors: Mar 15 – Mar 29 Transplant outdoors: Apr 26 – May 10
Cabbage	Start seeds indoors: Mar 15 – Mar 29 Transplant outdoors: Apr 26 – May 10
Onions (sets)	Plant outdoors: Apr 26 – May 10
Peas	Sow outdoors: Apr 12 – Apr 26
Spinach	Sow outdoors: Apr 12 – Apr 26
Lettuce	Sow outdoors: Apr 26 – May 10
Carrots	Sow outdoors: Apr 26 – May 10
Potatoes	Plant outdoors: Apr 26 – May 10
Beans	Sow outdoors: May 31 – Jun 7
Sweet corn	Sow outdoors: May 31 – Jun 7
Cucumbers	Sow outdoors: May 31 – Jun 7
Squash & zucchini	Sow outdoors: May 31 – Jun 7
Basil	Start seeds indoors: Apr 12 – Apr 26 Transplant outdoors: May 31 – Jun 7

Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Jul 30 (8 weeks before the average first fall frost on Sep 24).

Useful for zone 5a gardens

Seed starting kit with dome — to start seeds indoors before the last frost
LED grow light for seedlings — stops leggy seedlings
Frost cloth / plant covers — for late spring and early fall frosts
Soil thermometer — warm-season crops need soil above 60°F
Cold frame / mini greenhouse — adds weeks to a short season

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Frost risk in detail

	90% chance	50% chance	10% chance
Last 32°F frost in spring is after	May 8	May 24	Jun 9
First 32°F frost in fall is before	Oct 4	Sep 24	Sep 9

How to read it: in spring there is a 10% chance of a frost after June 9, so that is a safe date for tender plants. In fall there is a 10% chance of frost before September 9. A hard freeze (28°F) usually ends around May 9.

Hardiness zone by ZIP code in Rock Springs

82901 zone 5b
82902 zone 5a

Nearby cities

Riverton zone 4b, last frost May 12
Evanston zone 5a, last frost Jun 12
Jackson zone 4b, last frost Jun 20
Casper zone 5a, last frost May 10
Laramie zone 4a, last frost Jun 7
Sheridan zone 5a, last frost May 21
Cheyenne zone 5b, last frost May 14
Gillette zone 5a, last frost May 15

All cities in Wyoming → · Other zone 5a cities →

Questions

What growing zone is Rock Springs, WY?

Rock Springs is in USDA Plant Hardiness Zone 5a (average extreme winter low -20°F to -15°F), according to the USDA 2023 map. Some ZIP codes of the city fall in zone 5b.

When is the last frost in Rock Springs?

The average last spring frost (32°F) in Rock Springs is May 24. There is still a 10% chance of frost until June 9.

When can I plant tomatoes in Rock Springs?

Transplant tomatoes outdoors 1–2 weeks after the average last frost: around May 31 – Jun 7. Start seeds indoors 6–8 weeks before the last frost.

Frost dates: NOAA U.S. Climate Normals 1991–2020, station Rock Springs Fire Dept, WY (USC00487847), 3.2 km (2.0 mi) from the city center, elevation 1911 m, based on 18 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.