Frost dates for the Rapid City area
When the last spring frost and the first fall frost usually come. Use them to plan when to set out tender plants, and when to get cover crops and leaves on the soil.
These dates come from past weather records. No year is average, so treat them as odds, not promises, and check the forecast. Typical means half of years: in spring, the cold is over by then; in fall, it has arrived by then.
Spring: the last cold night
| Night at or below | Early year1 in 10 | Typicalhalf of years | Late year1 in 10 |
|---|---|---|---|
| Last hard freeze 28° | Apr 13 | Apr 28 | May 11 |
| Last frost 32° | Apr 27 | May 10 | May 25 |
| Last cold night 36° | May 8 | May 21 | Jun 1 |
Frost can form on leaves even when the air is a few degrees above freezing, especially on clear, calm nights and in low spots. That is why gardeners treat 36° as the danger line for tender plants such as tomatoes, peppers and squash. In half of years the last 36° night is past by May 21, and it is rare after June 1.
Fall: the first cold night
| Night at or below | Early year1 in 10 | Typicalhalf of years | Late year1 in 10 |
|---|---|---|---|
| First cold night 36° | Sep 7 | Sep 21 | Oct 3 |
| First frost 32° | Sep 16 | Oct 1 | Oct 14 |
| First hard freeze 28° | Sep 26 | Oct 9 | Oct 23 |
The first frost ends the season for tender plants, but the soil still needs cover. Sow cover crops early enough that they grow before the cold, and spread fallen leaves on bare beds.
Higher in the Hills
Frost comes later in spring as you go up. On SDSU's map of 1991–2020 records, most of the plains near Rapid City reach their typical last 32° night between May 10 and May 12, while much of the Black Hills does not until between May 13 and May 27. If you garden in the Hills, plan on the later end of these dates.
Then what?
In spring and fall, the Plan tab in My Soil shows a short frost reminder with these dates. Before the first fall frost is a good time to get the soil covered.
Where these dates come from
- National Gardening Association. The spring and fall tables: frost dates for Rapid City, SD.
- SDSU Extension and Mesonet. The Black Hills note: their map of the typical last spring frost, 1991–2020, made in 2022 by Bret Lang and Laura Edwards.