Nampa, Idaho: planting zone & frost dates
Nampa is in USDA plant hardiness zone 7a, where the average coldest winter night reaches 0 to 5°F (-17.8 to -15.0°C). The typical last spring frost is around May 5 and the first fall frost around Oct 6.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | May 18 | Sep 29 |
| Typical planning date (30% risk) | May 5 | Oct 6 |
| Median (50%) | Apr 29 | Oct 13 |
How to read this: after the spring "10% risk" date, a 32°F frost happens in only about 1 year in 10. In fall, the "10% risk" date is the early end — a frost before it happens about 1 year in 10.
Frost data comes from NOAA station NAMPA SUGAR FACTORY, ID (USC00106305), 1.4 mi (2.3 km) from the city center and 7 ft lower than the city center (-2 m). Record used for the 1991–2020 normals: 22 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Nampa
All 3 ZIP codes covering Nampa are in zone 7a.
Vegetable planting calendar for Nampa
Dates are counted from the 30%-risk frost dates above (last frost May 5, first frost Oct 6). Shift a week later in cold spots or low-lying ground.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Mar 10 – Mar 24 | May 12 – May 26 | — | — |
| Pepper | Feb 24 – Mar 10 | May 19 – Jun 2 | — | — |
| Lettuce | Mar 24 – Apr 7 | Apr 21 – May 12 | Apr 7 – May 19 | Jul 28 – Aug 25 |
| Green Beans | — | — | May 12 – Jun 16 | Jul 14 – Jul 28 |
| Sweet Corn | — | — | May 12 – Jun 9 | — |
| Zucchini & Summer Squash | Apr 7 – Apr 14 | May 12 – May 26 | May 12 – Jun 2 | Jul 14 – Jul 28 |
| Cucumber | Apr 7 – Apr 14 | May 19 – May 26 | May 12 – Jun 2 | Jul 14 – Jul 28 |
| Carrot | — | — | Apr 14 – May 19 | Jul 14 – Jul 28 |
| Onion | Feb 10 – Feb 24 | Apr 7 – Apr 21 | — | — |
| Potato | — | Apr 7 – Apr 28 | — | — |
| Basil | Mar 24 – Apr 7 | May 19 – Jun 2 | May 19 – Jun 9 | — |
| Spinach | — | — | Mar 24 – Apr 21 | Aug 11 – Sep 8 |
| Kale | Mar 10 – Mar 24 | Apr 7 – Apr 28 | Apr 7 – Apr 28 | Jul 28 – Aug 25 |
| Broccoli | Mar 10 – Mar 24 | Apr 21 – May 12 | — | Jul 14 – Jul 28 |
| Peas | — | — | Mar 24 – Apr 14 | Jul 28 – Aug 11 |
| Eggplant | Feb 24 – Mar 10 | May 19 – Jun 2 | — | — |
| Cabbage | Mar 10 – Mar 24 | Apr 7 – Apr 21 | — | Jul 14 – Jul 28 |
| Radish | — | — | Mar 31 – May 19 | Aug 25 – Sep 22 |
| Strawberry | — | Apr 7 – Apr 28 | — | — |
| Beets | — | — | Apr 14 – May 26 | Jul 28 – Aug 11 |
Nearby cities in Idaho
- Meridian — zone 7a, last frost May 5, first frost Oct 6
- Boise — zone 7a, last frost Apr 30, first frost Oct 14
More: all Idaho cities · other zone 7a cities: Louisville, KY, Wichita, KS, Cleveland, OH, Lexington, KY, St. Louis, MO, Boise, ID, Amarillo, TX, Providence, RI
Nampa gardening questions
When is the last frost in Nampa, ID?
Plan around May 5. At NOAA's Nampa Sugar Factory, ID station, 1.4 mi from the city center, there is a 30% chance of a 32°F frost after that date. Half of springs have their last frost by Apr 29, and after May 18 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Apr 11. The 90% and 10% dates are 33 days apart, close to the 36-day median for cities on this site.
When should I plant tomatoes in Nampa, ID?
Start seeds indoors Mar 10 – Mar 24 and set transplants outside May 12 – May 26, once nights stay above 50°F and the soil is near 60°F. That leaves 154 days between the 30% frost dates, enough for most varieties including 80–85-day slicers. More: tomato planting dates by zone.
How long is the growing season in Nampa?
About 164 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 142 days, and in 1 year in 10 it runs 186 days or more. In fall there is a 10% chance of frost by Sep 29 and a 30% chance by Oct 6. That is the shortest of the 3 Idaho cities on this site.
When should I plant a fall garden in Nampa?
Count back from the first fall frost (Oct 6): transplant broccoli Jul 14 – Jul 28; sow kale Jul 28 – Aug 25; sow lettuce Jul 28 – Aug 25; sow radishes Aug 25 – Sep 22. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Oct 25. How the math works: succession and fall planting.
Did Nampa's hardiness zone change on the 2023 map?
No. Going by the zone that covers most of the city's land, Nampa is zone 7a on both the 2012 and the 2023 USDA maps (PRISM/OSU ZIP listings). About 42% of U.S. ZIP codes kept their half-zone in 2023. Why the 2023 map is warmer.
How does Nampa compare with Boise, ID?
Both are in zone 7a. The typical last spring frost in Nampa (May 5) comes about 5 days later than in Boise, ID (Apr 30), 17 miles away, and the first fall frost is Oct 6 versus Oct 14. Nampa sits about 266 ft lower, which explains part of the gap. The two cities use different NOAA stations.