USDA Hardiness Zone 4a
Frost Dates for 58504 — Bismarck, North Dakota
NOAA 1991–2020 normals from Bismarck WFO, ND (1,651 ft), under a mile northwest.
Updated
In Bismarck, the last spring frost (32°F) is around May 14 in half of years and has passed by May 27 in nine years out of ten. The first fall frost comes around September 30, as early as September 18 one year in ten, leaving a typical freeze-free season of 138 days (NOAA, Bismarck WFO, ND).
- Last spring frost
- May 14
- First fall frost
- September 30
- Growing season
- 138 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
- October 29
- Last snow
- April 23
- Winters with snow
- 100%
- Snow per year
- 50.5"
median, 1991–2020
median, 1991–2020
30 of 30 observed
NOAA normal
Frost risk by date in Bismarck
Half of springs at Bismarck WFO, ND see their last 32°F night by May 14; only one in ten is past it by May 1, and one in ten still has one after May 27. Planting tender crops after May 19 leaves a 30% risk of a frost on them, after May 23 20%, and after May 27 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 21% of the 33 North Dakota stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 30 in half of years, as early as September 18 one year in ten, and holds off past October 13 one year in ten. A hard freeze of 28°F follows 8 days later, around October 8; in spring the one-in-ten date for 28°F is May 18, 9 days before the 32°F one. The freeze-free season lasts 138 days in a typical year, longer than at 55% of the 33 North Dakota stations; it reaches 156 days one year in ten and falls short of 119 one year in ten. On average 185 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 9 days longer, to about May 23, and return around September 21. Severe cold of 16°F or below comes every winter, usually between November 3 and April 4.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 12 | May 15 | May 18 | May 20 | May 23 | May 26 | May 28 | May 31 | Jun 5 |
| 32°F | May 1 | May 5 | May 8 | May 12 | May 14 | May 16 | May 19 | May 23 | May 27 |
| 28°F | Apr 17 | Apr 24 | Apr 28 | May 1 | May 3 | May 6 | May 10 | May 13 | May 18 |
| 24°F | Apr 7 | Apr 12 | Apr 16 | Apr 20 | Apr 23 | Apr 26 | Apr 30 | May 3 | May 9 |
| 20°F | Mar 31 | Apr 4 | Apr 7 | Apr 9 | Apr 12 | Apr 16 | Apr 18 | Apr 23 | Apr 29 |
| 16°F | Mar 18 | Mar 25 | Mar 30 | Apr 2 | Apr 4 | Apr 7 | Apr 10 | Apr 14 | Apr 19 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 8 | Sep 12 | Sep 16 | Sep 19 | Sep 21 | Sep 23 | Sep 26 | Sep 29 | Oct 3 |
| 32°F | Sep 18 | Sep 22 | Sep 25 | Sep 28 | Sep 30 | Oct 2 | Oct 5 | Oct 9 | Oct 13 |
| 28°F | Sep 25 | Sep 30 | Oct 3 | Oct 6 | Oct 8 | Oct 11 | Oct 14 | Oct 17 | Oct 21 |
| 24°F | Oct 4 | Oct 8 | Oct 12 | Oct 15 | Oct 18 | Oct 20 | Oct 23 | Oct 26 | Oct 30 |
| 20°F | Oct 12 | Oct 18 | Oct 21 | Oct 24 | Oct 26 | Oct 29 | Nov 1 | Nov 4 | Nov 9 |
| 16°F | Oct 21 | Oct 26 | Oct 29 | Nov 1 | Nov 3 | Nov 6 | Nov 9 | Nov 13 | Nov 19 |
Freeze probabilities 1991–2020 at Bismarck WFO, ND, 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 58504 →Compare Bismarck with another place →
Compared with the next station
The nearest other station, Bismarck 2.4 NNW, ND, 5 miles northwest of Bismarck and 180 feet higher, has a last frost 4 days earlier (May 10), the same first-frost date, a season 4 days longer.
When it snows in Bismarck, North Dakota
The first measurable snow (0.1 inch or more) in Bismarck usually arrives around October 29, and the last of the season around April 23. Those are the middle dates across the winters of 1991–2020 at Bismarck, ND, 0.3 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 21 days after the last snow.
Planting calendar for 58504
| When | What to do |
|---|---|
| March 5 – March 19 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 19 – April 2 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 16 – April 30 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 14 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 8 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 16 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 30 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 58504 is under a mile from Bismarck WFO, ND, which stands at 1,651 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 58504 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 North 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.