Frost dates for Bismarck, North Dakota
In Bismarck, half of springs have had their last frost by May 14 (and 1 spring in 10 still has one after May 27), and half of falls have had their first frost by September 27, leaving about 136 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
Bismarck, North Dakota
Last spring frost
May 14
Half of springs have their last frost by this date. For a safer bet, wait until May 27: only 1 spring in 10 has a frost after that.
First fall frost
September 27
Half of falls have their first frost by this date. In 1 fall in 10 it comes by September 15.
Growing season
136 days
Frost-free days in a typical year. 9 years in 10 get at least 117.
Hardiness zone
4a
2023 USDA map: the coldest night of winter averages −30°F to −25°F. It was 4a on the 2012 map too. All 3 ZIP codes within about 6 miles of the city's center are in zone 4a.
Print a year planner for Bismarck
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 1 | May 14 | May 27 |
| First frost in fall | September 15 | September 27 | October 9 |
The frost-free season between them runs 136 days in a typical year. In 1 year in 10 it is 153 days or longer, and in 1 year in 10 it is 117 days or shorter.
- Hard freeze (28°F): typically last on May 3 and first on October 5. 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 May 25 and first on September 19. 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 Bismarck comes between May 1 and May 27, a window of 26 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 North Dakota's 125 NOAA stations with a frost every year, 41 percent have their typical last frost later than Bismarck does.
Planting calendar for Bismarck
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 |
|---|---|---|
| February | ||
| February 26 to March 26 | Broccoli and cabbage Start seeds indoors | 5 to 7 weeks before planting them out |
| March | ||
| March 12 to April 9 | Cauliflower Start seeds indoors | 5 to 7 weeks before planting out |
| March 26 to April 16 | Eggplant Start seeds indoors | 6 to 9 weeks before planting out |
| April | ||
| April 2 to 16 | Peppers Start seeds indoors | 6 to 8 weeks before planting out |
| April 9 to 23 | Tomatoes Start seeds indoors | 5 to 7 weeks before planting out |
| April 16 to 30 | Peas, spinach, lettuce, radishes, onion sets, turnips Sow outdoors, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April 16 to 30 | Broccoli and cabbage Plant out, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April 30 to May 14 | Beets, carrots, potatoes, Swiss chard Plant outdoors, as early as | semi-hardy crops: up to 2 weeks before the typical last frost |
| April 30 to May 14 | Cauliflower Plant out, as early as | semi-hardy: up to 2 weeks before the typical last frost |
| May | ||
| May 14 | Snap beans, sweet corn, cucumbers, summer squash Sow outdoors around | tender crops: around the typical last frost date |
| May 28 | Tomatoes, peppers, eggplant Plant out from | very tender: 2 weeks or more after the typical last frost |
| May 28 | Melons, winter squash, pumpkins, lima beans Sow outdoors from | very tender: 2 weeks or more after the typical last frost |
| July | ||
| July 1 | 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 5 | Carrots for fall Last date to sow | 70 days to harvest, plus 2 weeks for slower fall growth |
| July 6 | 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 10 | Peas for fall Last date to sow | 65 days to harvest, plus 2 weeks for slower fall growth |
| July 11 | 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 15 | Leaf lettuce and beets for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth |
| July 25 | Turnips and kohlrabi for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth |
| August | ||
| August 4 | Spinach for fall Last date to sow | 40 days to harvest, plus 2 weeks for slower fall growth |
| August 14 | Radishes for fall Last date to sow | 30 days to harvest, plus 2 weeks for slower fall growth |
| September | ||
| September 15 | 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 12 to 19 | 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 May 27, 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 Bismarck (station USW00024011), 3 miles from the center of Bismarck. It sits 100 feet lower, at 1,660 feet above sea level. NOAA rates this station's record as standard: at least 24 of the 30 years, with gaps filled from nearby stations.
The same station also gives the frost dates for Mandan.
Our ZIP code lookup matches these 3 ZIP codes to the same station, so they get the same dates: 58501, 58504, 58558. Hardiness zones are worked out separately for each ZIP code.
The nearest other places with pages
- Aberdeen, South Dakota: last frost around May 9, first frost around September 26 (145 miles away)
See frost dates across North Dakota, or look up your own ZIP code for the station nearest you. Want the background? Read what a last frost date really means.