Frost dates for Nampa, Idaho
In Nampa, half of springs have had their last frost by April 29 (and 1 spring in 10 still has one after May 18), and half of falls have had their first frost by October 13, leaving about 164 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
Nampa, Idaho
Last spring frost
April 29
Half of springs have their last frost by this date. For a safer bet, wait until May 18: only 1 spring in 10 has a frost after that.
First fall frost
October 13
Half of falls have their first frost by this date. In 1 fall in 10 it comes by September 29.
Growing season
164 days
Frost-free days in a typical year. 9 years in 10 get at least 142.
Hardiness zone
7a
2023 USDA map: the coldest night of winter averages 0°F to 5°F. It was 7a on the 2012 map too. All 2 ZIP codes within about 6 miles of the city's center are in zone 7a.
Print a year planner for Nampa
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 | April 15 | April 29 | May 18 |
| First frost in fall | September 29 | October 13 | October 28 |
The frost-free season between them runs 164 days in a typical year. In 1 year in 10 it is 186 days or longer, and in 1 year in 10 it is 142 days or shorter.
- Hard freeze (28°F): typically last on April 11 and first on October 25. 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 16 and first on September 30. 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 Nampa comes between April 15 and May 18, a window of 33 days. That is about average for NOAA's stations (the typical window is 31 days).
Among Idaho's 127 NOAA stations with a frost every year, 84 percent have their typical last frost later than Nampa does.
Planting calendar for Nampa
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: 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 11 to March 11 | Broccoli and cabbage Start seeds indoors | 5 to 7 weeks before planting them out |
| February 25 to March 25 | Cauliflower Start seeds indoors | 5 to 7 weeks before planting out |
| March | ||
| March 11 to April 1 | Eggplant Start seeds indoors | 6 to 9 weeks before planting out |
| March 18 to April 1 | Peppers Start seeds indoors | 6 to 8 weeks before planting out |
| March 25 to April 8 | Tomatoes Start seeds indoors | 5 to 7 weeks before planting out |
| April | ||
| April 1 to 15 | Peas, spinach, lettuce, radishes, onion sets, turnips Sow outdoors, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April 1 to 15 | Broccoli and cabbage Plant out, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April 15 to 29 | Beets, carrots, potatoes, Swiss chard Plant outdoors, as early as | semi-hardy crops: up to 2 weeks before the typical last frost |
| April 15 to 29 | Cauliflower Plant out, as early as | semi-hardy: up to 2 weeks before the typical last frost |
| April 29 | Snap beans, sweet corn, cucumbers, summer squash Sow outdoors around | tender crops: around the typical last frost date |
| May | ||
| May 13 | Tomatoes, peppers, eggplant Plant out from | very tender: 2 weeks or more after the typical last frost |
| May 13 | Melons, winter squash, pumpkins, lima beans Sow outdoors from | very tender: 2 weeks or more after the typical last frost |
| June | ||
| June 7 to 21 | Broccoli for fall Start seeds | set the plants out by July 26 |
| July | ||
| July 17 | 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 21 | Carrots for fall Last date to sow | 70 days to harvest, plus 2 weeks for slower fall growth |
| July 22 | 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 26 | Peas for fall Last date to sow | 65 days to harvest, plus 2 weeks for slower fall growth |
| July 27 | 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 31 | Leaf lettuce and beets for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth |
| August | ||
| August 10 | Turnips and kohlrabi for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth |
| August 20 | Spinach for fall Last date to sow | 40 days to harvest, plus 2 weeks for slower fall growth |
| August 30 | Radishes for fall Last date to sow | 30 days to harvest, plus 2 weeks for slower fall growth |
| September | ||
| September 29 | 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 |
| November | ||
| November 1 to 8 | 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 19 days later. That plans around May 18, 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 Nampa Sugar Factory (station USC00106305), 1 mile from the center of Nampa. It sits at about the same elevation, 2,470 feet above sea level. NOAA rates this station's record as representative: at least 10 of the 30 years, with the gaps filled from nearby stations.
The same station also gives the frost dates for Caldwell, Eagle, Star and Middleton.
Our ZIP code lookup matches these 10 ZIP codes to the same station, so they get the same dates: 83605, 83607, 83616, 83641, 83644, 83646, 83651, 83669, 83686, 83687. Hardiness zones are worked out separately for each ZIP code.
Nearby places
- Boise, Idaho: last frost around April 24, first frost around October 21 (15 miles away)
See frost dates across Idaho, or look up your own ZIP code for the station nearest you. Want the background? Read what a last frost date really means.