Frost dates for Gillette, Wyoming
In Gillette, half of springs have had their last frost by May 22 (and 1 spring in 10 still has one after June 4), and half of falls have had their first frost by September 25, leaving about 125 frost-free days in a typical year. Here is how sure those dates are, what they mean for planting, and where they come from.
Frost dates for
Gillette, Wyoming
Last spring frost
May 22
Half of springs have their last frost by this date. For a safer bet, wait until June 4: only 1 spring in 10 has a frost after that.
First fall frost
September 25
Half of falls have their first frost by this date. In 1 fall in 10 it comes by September 9.
Growing season
125 days
Frost-free days in a typical year. 9 years in 10 get at least 106.
Hardiness zone
5a
2023 USDA map: the coldest night of winter averages −20°F to −15°F. On the 2012 map it was 4b, half a zone colder. All 2 ZIP codes within about 6 miles of the city's center are in zone 5a.
Print a year planner for Gillette
Frost risk through the year
How sure are these dates?
A frost date is a probability, not a promise. NOAA worked out, from 30 years of nightly lows, how often the last spring frost and the first fall frost fall on each date. The middle column is the typical year. The outer columns are the early and late years that come about once a decade.
| Early year 1 in 10 | Typical year 1 in 2 | Late year 1 in 10 | |
|---|---|---|---|
| Last frost in spring | May 8 | May 22 | June 4 |
| First frost in fall | September 9 | September 25 | October 8 |
The frost-free season between them runs 125 days in a typical year. In 1 year in 10 it is 146 days or longer, and in 1 year in 10 it is 106 days or shorter.
- Hard freeze (28°F): typically last on May 9 and first on October 4. It is a harder freeze than the 32°F frost line, cold enough to damage many garden plants; how hardy a crop is decides whether it comes through. (The National Weather Service's own hard-freeze threshold varies from office to office.)
- Frost possible (36°F at the station): typically last on June 3 and first on September 15. On clear, still nights the ground can be several degrees colder than the thermometer, so frost can form on plants when the official reading is in the mid-30s.
In 8 springs out of 10, the last frost in Gillette comes between May 8 and June 4, a window of 27 days. That is narrower than at most NOAA stations (the typical window is 31 days), so the typical date is a steadier guide here than in most places.
Among Wyoming's 129 NOAA stations with a frost every year, 38 percent have their typical last frost later than Gillette does.
Planting calendar for Gillette
These dates count from the typical last and first frosts, using the planting rules published by Colorado State University Extension (spring), Virginia Cooperative Extension (fall crops) and University of Minnesota Extension (garlic, where winters are hard). Weather in any one year can run early or late, so check the forecast before you plant tender crops.
Your season is too short for a separate fall planting of cabbage and broccoli: sown late enough to be a fall crop, it wouldn't be ready before the typical first frost. Your spring planting is your harvest.
| When | What to do | Why then |
|---|---|---|
| March | ||
| March 6 to April 3 | Broccoli and cabbage Start seeds indoors | 5 to 7 weeks before planting them out |
| March 20 to April 17 | Cauliflower Start seeds indoors | 5 to 7 weeks before planting out |
| April | ||
| April 3 to 24 | Eggplant Start seeds indoors | 6 to 9 weeks before planting out |
| April 10 to 24 | Peppers Start seeds indoors | 6 to 8 weeks before planting out |
| April 17 to May 1 | Tomatoes Start seeds indoors | 5 to 7 weeks before planting out |
| April 24 to May 8 | Peas, spinach, lettuce, radishes, onion sets, turnips Sow outdoors, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April 24 to May 8 | Broccoli and cabbage Plant out, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| May | ||
| May 8 to 22 | Beets, carrots, potatoes, Swiss chard Plant outdoors, as early as | semi-hardy crops: up to 2 weeks before the typical last frost |
| May 8 to 22 | Cauliflower Plant out, as early as | semi-hardy: up to 2 weeks before the typical last frost |
| May 22 | Snap beans, sweet corn, cucumbers, summer squash Sow outdoors around | tender crops: around the typical last frost date |
| June | ||
| June 5 | Tomatoes, peppers, eggplant Plant out from | very tender: 2 weeks or more after the typical last frost |
| June 5 | Melons, winter squash, pumpkins, lima beans Sow outdoors from | very tender: 2 weeks or more after the typical last frost |
| June 29 | Snap beans for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July | ||
| July 3 | Carrots for fall Last date to sow | 70 days to harvest, plus 2 weeks for slower fall growth |
| July 4 | Cucumbers for fall Last date to sow | 55 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July 8 | Peas for fall Last date to sow | 65 days to harvest, plus 2 weeks for slower fall growth |
| July 9 | Summer squash for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July 13 | Leaf lettuce and beets for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth |
| July 23 | Turnips and kohlrabi for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth |
| August | ||
| August 2 | Spinach for fall Last date to sow | 40 days to harvest, plus 2 weeks for slower fall growth |
| August 12 | Radishes for fall Last date to sow | 30 days to harvest, plus 2 weeks for slower fall growth |
| September | ||
| September 9 | Tomatoes, peppers, squash, melons, cucumbers Watch the forecast from | in 1 fall in 10 the first frost comes by this date; pick tender crops before a frost |
| October | ||
| October 11 to 18 | Garlic Plant cloves | one or two weeks after the typical first hard freeze (28°F), our reading of the first killing frost |
Want more insurance? Shift every spring date 13 days later. That plans around June 4, the date after which only 1 spring in 10 has a frost.
For spring bulbs such as tulips and daffodils, plant once the soil has cooled to about 50 to 55°F and keep going until a couple of weeks before the ground freezes. Our guide to fall planting explains how to tell.
Where these numbers come from
These dates come from NOAA's weather station Gillette Campbell Airport (station USW00094023), 5 miles from the center of Gillette. It sits 200 feet lower, at 4,350 feet above sea level. NOAA rates this station's record as representative: at least 10 of the 30 years, with the gaps filled from nearby stations.
The nearest other places with pages
- Casper, Wyoming: last frost around May 26, first frost around September 22 (105 miles away)
- Rapid City, South Dakota: last frost around May 12, first frost around October 1 (115 miles away)
See frost dates across Wyoming, or look up your own ZIP code for the station nearest you. Want the background? Read what a last frost date really means.