Frost dates for Rapid City, South Dakota
In Rapid City, half of springs have had their last frost by May 12 (and 1 spring in 10 still has one after May 26), and half of falls have had their first frost by October 1, leaving about 139 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
Rapid City, South Dakota
Last spring frost
May 12
Half of springs have their last frost by this date. For a safer bet, wait until May 26: only 1 spring in 10 has a frost after that.
First fall frost
October 1
Half of falls have their first frost by this date. In 1 fall in 10 it comes by September 16.
Growing season
139 days
Frost-free days in a typical year. 9 years in 10 get at least 120.
Hardiness zone
5a
2023 USDA map: the coldest night of winter averages −20°F to −15°F. It was 5a on the 2012 map too. ZIP codes within about 6 miles of the city's center: 1 in 5a and 1 in 5b.
Stations near you disagree. NOAA's Rapid City Regional Airport (8 miles away, at 3,160 feet above sea level), the one we used, gives a typical last frost of May 12 and a typical first frost of October 1. NOAA's Pactola Dam (15 miles away, at 4,720 feet above sea level) gives a typical last frost of May 28 and a typical first frost of September 18. So the typical last frost could fall anywhere from May 12 to 28 and the typical first frost from September 18 to October 1, depending on whether your garden is more like one or the other. Local terrain matters: hillsides, valley floors, water and city heat can change frost dates a lot over a few miles. Treat the dates here as a starting point, and compare with a nearby gardener or your county extension office.
Print a year planner for Rapid City
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 12 | May 26 |
| First frost in fall | September 16 | October 1 | October 14 |
The frost-free season between them runs 139 days in a typical year. In 1 year in 10 it is 157 days or longer, and in 1 year in 10 it is 120 days or shorter.
- Hard freeze (28°F): typically last on May 2 and first on October 9. 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 22 and first on September 21. 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 Rapid City comes between May 1 and May 26, a window of 25 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 South Dakota's 166 NOAA stations with a frost every year, 23 percent have their typical last frost later than Rapid City does.
Planting calendar for Rapid City
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 24 to March 24 | Broccoli and cabbage Start seeds indoors | 5 to 7 weeks before planting them out |
| March | ||
| March 10 to April 7 | Cauliflower Start seeds indoors | 5 to 7 weeks before planting out |
| March 24 to April 14 | Eggplant Start seeds indoors | 6 to 9 weeks before planting out |
| March 31 to April 14 | Peppers Start seeds indoors | 6 to 8 weeks before planting out |
| April | ||
| April 7 to 21 | Tomatoes Start seeds indoors | 5 to 7 weeks before planting out |
| April 14 to 28 | Peas, spinach, lettuce, radishes, onion sets, turnips Sow outdoors, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April 14 to 28 | Broccoli and cabbage Plant out, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April 28 to May 12 | Beets, carrots, potatoes, Swiss chard Plant outdoors, as early as | semi-hardy crops: up to 2 weeks before the typical last frost |
| April 28 to May 12 | Cauliflower Plant out, as early as | semi-hardy: up to 2 weeks before the typical last frost |
| May | ||
| May 12 | Snap beans, sweet corn, cucumbers, summer squash Sow outdoors around | tender crops: around the typical last frost date |
| May 26 | Tomatoes, peppers, eggplant Plant out from | very tender: 2 weeks or more after the typical last frost |
| May 26 | Melons, winter squash, pumpkins, lima beans Sow outdoors from | very tender: 2 weeks or more after the typical last frost |
| July | ||
| July 5 | 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 9 | Carrots for fall Last date to sow | 70 days to harvest, plus 2 weeks for slower fall growth |
| July 10 | 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 14 | Peas for fall Last date to sow | 65 days to harvest, plus 2 weeks for slower fall growth |
| July 15 | 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 19 | Leaf lettuce and beets for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth |
| July 29 | Turnips and kohlrabi for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth |
| August | ||
| August 8 | Spinach for fall Last date to sow | 40 days to harvest, plus 2 weeks for slower fall growth |
| August 18 | Radishes for fall Last date to sow | 30 days to harvest, plus 2 weeks for slower fall growth |
| September | ||
| September 16 | 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 16 to 23 | 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 14 days later. That plans around May 26, 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 Rapid City Regional Airport (station USW00024090), 8 miles from the center of Rapid City. It sits 120 feet lower, at 3,160 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 Box Elder.
Our ZIP code lookup matches these 4 ZIP codes to the same station, so they get the same dates: 57703, 57706, 57738, 57761. Hardiness zones are worked out separately for each ZIP code.
The nearest other places with pages
- Gillette, Wyoming: last frost around May 22, first frost around September 25 (115 miles away)
See frost dates across South Dakota, or look up your own ZIP code for the station nearest you. Want the background? Read what a last frost date really means.