USDA Hardiness Zone 4a
Frost Dates for 57445 — Groton, South Dakota
NOAA 1991–2020 normals from Andover #2, SD (1,478 ft), 12 miles east.
Updated
In Groton, the last spring frost (32°F) is around May 6 in half of years and has passed by May 21 in nine years out of ten. The first fall frost comes around October 4, as early as September 21 one year in ten, leaving a typical freeze-free season of 150 days (NOAA, Andover #2, SD).
- Last spring frost
- May 6
- First fall frost
- October 4
- Growing season
- 150 days
- Hardiness zone
- 4a
50% probability
50% probability
freeze-free, 50%
-30 to -25°F (-34.4 to -31.7°C) coldest night
- First snow
- November 15
- Last snow
- April 1
- Winters with snow
- 100%
- Snow per year
- 32.3"
median, 1991–2020
median, 1991–2020
15 of 15 observed
NOAA normal
Frost risk by date in Groton
Half of springs at Andover #2, SD see their last 32°F night by May 6; only one in ten is past it by April 22, and one in ten still has one after May 21. Planting tender crops after May 12 leaves a 30% risk of a frost on them, after May 16 20%, and after May 21 10%. The 15 days between the even-odds date and the one-in-ten date is wider than at 84% of the 49 South Dakota stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 4 in half of years, as early as September 21 one year in ten, and holds off past October 19 one year in ten. A hard freeze of 28°F follows 10 days later, around October 14; in spring the one-in-ten date for 28°F is May 12, 9 days before the 32°F one. The freeze-free season lasts 150 days in a typical year, longer than at 53% of the 49 South Dakota stations; it reaches 169 days one year in ten and falls short of 132 one year in ten. On average 165 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 10 days longer, to about May 16, and return around September 26. Severe cold of 16°F or below comes every winter, usually between November 8 and April 1.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 30 | May 6 | May 9 | May 13 | May 16 | May 19 | May 22 | May 25 | May 29 |
| 32°F | Apr 22 | Apr 28 | Apr 30 | May 3 | May 6 | May 8 | May 12 | May 16 | May 21 |
| 28°F | Apr 12 | Apr 17 | Apr 22 | Apr 25 | Apr 28 | May 1 | May 3 | May 7 | May 12 |
| 24°F | Apr 3 | Apr 8 | Apr 11 | Apr 15 | Apr 18 | Apr 22 | Apr 26 | Apr 30 | May 3 |
| 20°F | Mar 24 | Mar 31 | Apr 3 | Apr 6 | Apr 9 | Apr 12 | Apr 15 | Apr 20 | Apr 26 |
| 16°F | Mar 15 | Mar 21 | Mar 25 | Mar 29 | Apr 1 | Apr 4 | Apr 7 | Apr 11 | Apr 17 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 12 | Sep 17 | Sep 20 | Sep 23 | Sep 26 | Sep 28 | Sep 30 | Oct 3 | Oct 7 |
| 32°F | Sep 21 | Sep 27 | Sep 30 | Oct 2 | Oct 4 | Oct 6 | Oct 10 | Oct 13 | Oct 19 |
| 28°F | Oct 1 | Oct 4 | Oct 7 | Oct 11 | Oct 14 | Oct 17 | Oct 20 | Oct 23 | Oct 27 |
| 24°F | Oct 8 | Oct 13 | Oct 17 | Oct 20 | Oct 24 | Oct 27 | Oct 30 | Nov 2 | Nov 6 |
| 20°F | Oct 17 | Oct 23 | Oct 27 | Oct 30 | Nov 1 | Nov 4 | Nov 6 | Nov 10 | Nov 15 |
| 16°F | Oct 25 | Oct 31 | Nov 2 | Nov 5 | Nov 8 | Nov 10 | Nov 14 | Nov 17 | Nov 23 |
Freeze probabilities 1991–2020 at Andover #2, 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 57445 →Compare Groton with another place →
Weather by month in Groton
July is the warmest month at Andover #2, SD, averaging 82°F by day and 61°F at night; January is the coldest at 22°F and 5°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 68% of years.
Warmth for growing adds up to 2,564 growing degree days a year (base 50°F), fewer than at 67% of the 49 South Dakota stations. 32% of them (831) have built up by the end of June, and July adds the most, 666.
| Month | High °F | Low °F | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|
| Jan | 22 | 5 | 100% | 31 | 0 |
| Feb | 27 | 9 | 100% | 27 | 0 |
| Mar | 40 | 21 | 100% | 25 | 12 |
| Apr | 56 | 33 | 100% | 14 | 61 |
| May | 68 | 46 | 68% | 3 | 255 |
| Jun | 77 | 56 | 0% | 0 | 504 |
| Jul | 82 | 61 | 0% | 0 | 666 |
| Aug | 80 | 59 | 0% | 0 | 614 |
| Sep | 73 | 50 | 33% | <1 | 355 |
| Oct | 58 | 37 | 100% | 11 | 92 |
| Nov | 41 | 23 | 100% | 23 | 6 |
| Dec | 28 | 11 | 100% | 31 | 0 |
Monthly normals 1991–2020 at Andover #2, SD (1,478 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, Aberdeen 3 E, SD, 14 miles west of Groton and 177 feet lower, has a last frost 2 days later (May 8), a first frost 5 days earlier (September 29), a season 6 days shorter.
When it snows in Groton, South Dakota
The first measurable snow (0.1 inch or more) in Groton usually arrives around November 15, and the last of the season around April 1. Those are the middle dates across the winters of 1991–2020 at Groton, SD, 2 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 35 days after the last snow.
Planting calendar for 57445
| When | What to do |
|---|---|
| February 25 – March 11 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 11 – March 25 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 8 – April 22 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 6 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 12 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 20 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 4 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 57445 is 12 miles from Andover #2, SD, which stands at 1,478 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 57445 in zone 4a, the band where the coldest night of the year averaged -30 to -25°F (-34.4 to -31.7°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.