USDA Hardiness Zone 5a
Frost Dates for 57730 — Custer, South Dakota
NOAA 1991–2020 normals from Custer, SD (5,480 ft), 2 miles southeast.
Updated
In Custer, the last spring frost (32°F) is around May 18 in half of years and has passed by June 1 in nine years out of ten. The first fall frost comes around September 28, as early as September 10 one year in ten, leaving a typical freeze-free season of 129 days (NOAA, Custer, SD).
- Last spring frost
- May 18
- First fall frost
- September 28
- Growing season
- 129 days
- Hardiness zone
- 5a
50% probability
50% probability
freeze-free, 50%
-20 to -15°F (-28.9 to -26.1°C) coldest night
- First snow
- October 10
- Last snow
- May 1
- Winters with snow
- 100%
- Snow per year
- 57.9"
median, 1991–2020
median, 1991–2020
26 of 26 observed
NOAA normal
Frost risk by date in Custer
Half of springs at Custer, SD see their last 32°F night by May 18; only one in ten is past it by May 5, and one in ten still has one after June 1. Planting tender crops after May 25 leaves a 30% risk of a frost on them, after May 29 20%, and after June 1 10%. The 14 days between the even-odds date and the one-in-ten date is wider than at 59% of the 49 South Dakota stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 28 in half of years, as early as September 10 one year in ten, and holds off past October 10 one year in ten. A hard freeze of 28°F follows 6 days later, around October 4; in spring the one-in-ten date for 28°F is May 22, 10 days before the 32°F one. The freeze-free season lasts 129 days in a typical year, shorter than at 96% of the 49 South Dakota stations; it reaches 149 days one year in ten and falls short of 110 one year in ten. On average 181 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 12 days longer, to about May 30, and return around September 17. Severe cold of 16°F or below comes every winter, usually between November 1 and April 5.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 16 | May 21 | May 24 | May 27 | May 30 | Jun 1 | Jun 4 | Jun 8 | Jun 15 |
| 32°F | May 5 | May 9 | May 12 | May 15 | May 18 | May 21 | May 25 | May 29 | Jun 1 |
| 28°F | Apr 23 | Apr 28 | May 1 | May 3 | May 6 | May 9 | May 12 | May 16 | May 22 |
| 24°F | Apr 11 | Apr 15 | Apr 19 | Apr 21 | Apr 25 | Apr 28 | Apr 30 | May 4 | May 8 |
| 20°F | Mar 31 | Apr 4 | Apr 7 | Apr 11 | Apr 14 | Apr 17 | Apr 21 | Apr 25 | Apr 30 |
| 16°F | Mar 15 | Mar 23 | Mar 29 | Apr 1 | Apr 5 | Apr 8 | Apr 12 | Apr 16 | Apr 21 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 3 | Sep 6 | Sep 10 | Sep 14 | Sep 17 | Sep 20 | Sep 22 | Sep 26 | Oct 1 |
| 32°F | Sep 10 | Sep 17 | Sep 21 | Sep 25 | Sep 28 | Sep 30 | Oct 2 | Oct 5 | Oct 10 |
| 28°F | Sep 20 | Sep 25 | Sep 29 | Oct 1 | Oct 4 | Oct 7 | Oct 11 | Oct 14 | Oct 19 |
| 24°F | Sep 27 | Oct 3 | Oct 6 | Oct 10 | Oct 13 | Oct 16 | Oct 19 | Oct 24 | Oct 29 |
| 20°F | Oct 6 | Oct 11 | Oct 16 | Oct 18 | Oct 22 | Oct 25 | Oct 30 | Nov 2 | Nov 7 |
| 16°F | Oct 14 | Oct 19 | Oct 23 | Oct 27 | Nov 1 | Nov 4 | Nov 8 | Nov 12 | Nov 18 |
Freeze probabilities 1991–2020 at Custer, SD, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 57730 →Compare Custer with another place →
Weather by month in Custer
July is the warmest month at Custer, SD, averaging 80°F by day and 56°F at night; December is the coldest at 37°F and 17°F. A freezing night is all but certain in every month from October to May (a 90% chance or more). From July to August the chance of a 32°F night stays under 10% each month. In spring, June still brings one in 11% of years.
Warmth for growing adds up to 1,922 growing degree days a year (base 50°F), fewer than at 98% of the 49 South Dakota stations. 26% of them (493) have built up by the end of June, and July adds the most, 558. Precipitation totals 20.7 inches a year, most in May (3.5") and least in January (0.4"); May to September bring 68% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 37 | 16 | 0.4 | 100% | 30 | 0 |
| Feb | 37 | 16 | 0.7 | 100% | 26 | 0 |
| Mar | 46 | 24 | 0.9 | 100% | 26 | 6 |
| Apr | 51 | 31 | 2.2 | 100% | 20 | 22 |
| May | 61 | 41 | 3.5 | 96% | 7 | 127 |
| Jun | 72 | 50 | 3.4 | 11% | 1 | 337 |
| Jul | 80 | 56 | 3.2 | 0% | 0 | 558 |
| Aug | 79 | 55 | 2.4 | 0% | 0 | 517 |
| Sep | 71 | 46 | 1.5 | 60% | 2 | 285 |
| Oct | 56 | 34 | 1.5 | 100% | 15 | 61 |
| Nov | 45 | 24 | 0.6 | 100% | 25 | 8 |
| Dec | 37 | 17 | 0.4 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Custer, SD (5,480 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Johnson Siding, SD, 23 miles northeast of Custer and 1,296 feet lower, has a last frost 2 days later (May 20), a first frost 3 days earlier (September 25), a season 3 days shorter.
When it snows in Custer, South Dakota
The first measurable snow (0.1 inch or more) in Custer usually arrives around October 10, and the last of the season around May 1. Those are the middle dates across the winters of 1991–2020 at Custer, SD, 1.6 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 17 days after the last snow.
Planting calendar for 57730
| When | What to do |
|---|---|
| March 9 – March 23 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 23 – April 6 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 20 – May 4 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 18 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 6 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 14 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 28 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 57730 is 2 miles from Custer, SD, which stands at 5,480 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 57730 in zone 5a, the band where the coldest night of the year averaged -20 to -15°F (-28.9 to -26.1°C) over 1991–2020; a zone describes winter lows, not frost dates.
Frost dates across South Dakota →
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.