Boise, Idaho: planting zone & frost dates
Boise 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 Apr 30 and the first fall frost around Oct 14.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | May 9 | Oct 5 |
| Typical planning date (30% risk) | Apr 30 | Oct 14 |
| Median (50%) | Apr 24 | Oct 21 |
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 BOISE AIR TERMINAL, ID (USW00024131), 2.3 mi (3.7 km) from the city center and 72 ft higher than the city center (+22 m). Record used for the 1991–2020 normals: 27 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Boise
Boise spans more than one half-zone. Share of the city's land area by zone (via its 11 ZIP codes): 7a (83%), 6b (17%). The headline zone is the one covering the most land. Look up your ZIP for your exact zone.
Vegetable planting calendar for Boise
Dates are counted from the 30%-risk frost dates above (last frost Apr 30, first frost Oct 14). 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 5 – Mar 19 | May 7 – May 21 | — | — |
| Pepper | Feb 19 – Mar 5 | May 14 – May 28 | — | — |
| Lettuce | Mar 19 – Apr 2 | Apr 16 – May 7 | Apr 2 – May 14 | Aug 5 – Sep 2 |
| Green Beans | — | — | May 7 – Jun 11 | Jul 22 – Aug 5 |
| Sweet Corn | — | — | May 7 – Jun 4 | — |
| Zucchini & Summer Squash | Apr 2 – Apr 9 | May 7 – May 21 | May 7 – May 28 | Jul 22 – Aug 5 |
| Cucumber | Apr 2 – Apr 9 | May 14 – May 21 | May 7 – May 28 | Jul 22 – Aug 5 |
| Carrot | — | — | Apr 9 – May 14 | Jul 22 – Aug 5 |
| Onion | Feb 5 – Feb 19 | Apr 2 – Apr 16 | — | — |
| Potato | — | Apr 2 – Apr 23 | — | — |
| Basil | Mar 19 – Apr 2 | May 14 – May 28 | May 14 – Jun 4 | — |
| Spinach | — | — | Mar 19 – Apr 16 | Aug 19 – Sep 16 |
| Kale | Mar 5 – Mar 19 | Apr 2 – Apr 23 | Apr 2 – Apr 23 | Aug 5 – Sep 2 |
| Broccoli | Mar 5 – Mar 19 | Apr 16 – May 7 | — | Jul 22 – Aug 5 |
| Peas | — | — | Mar 19 – Apr 9 | Aug 5 – Aug 19 |
| Eggplant | Feb 19 – Mar 5 | May 14 – May 28 | — | — |
| Cabbage | Mar 5 – Mar 19 | Apr 2 – Apr 16 | — | Jul 22 – Aug 5 |
| Radish | — | — | Mar 26 – May 14 | Sep 2 – Sep 30 |
| Strawberry | — | Apr 2 – Apr 23 | — | — |
| Beets | — | — | Apr 9 – May 21 | Aug 5 – Aug 19 |
Nearby cities in Idaho
- Meridian — zone 7a, last frost May 5, first frost Oct 6
- Nampa — zone 7a, last frost May 5, first frost Oct 6
More: all Idaho cities · other zone 7a cities: Louisville, KY, Wichita, KS, Cleveland, OH, Lexington, KY, St. Louis, MO, Amarillo, TX, Providence, RI, Paterson, NJ
Boise gardening questions
When is the last frost in Boise, ID?
Plan around Apr 30. At NOAA's Boise Air Terminal, ID station, 2.3 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 24, and after May 9 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Apr 2. The 90% and 10% dates are 35 days apart, close to the 36-day median for cities on this site.
When should I plant tomatoes in Boise, ID?
Start seeds indoors Mar 5 – Mar 19 and set transplants outside May 7 – May 21, once nights stay above 50°F and the soil is near 60°F. That leaves 167 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 Boise?
About 179 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 156 days, and in 1 year in 10 it runs 203 days or more. In fall there is a 10% chance of frost by Oct 5 and a 30% chance by Oct 14. That is the longest of the 3 Idaho cities on this site.
When should I plant a fall garden in Boise?
Count back from the first fall frost (Oct 14): transplant broccoli Jul 22 – Aug 5; sow kale Aug 5 – Sep 2; sow lettuce Aug 5 – Sep 2; sow radishes Sep 2 – Sep 30. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Oct 31. How the math works: succession and fall planting.
Did Boise's hardiness zone change on the 2023 map?
No. Going by the zone that covers most of the city's land, Boise 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.
Is all of Boise in zone 7a?
No. Zone 7a covers about 83% of the city's land; the rest is in 6b (17%), measured across the city's 11 ZIP codes. Check your own ZIP code in the table above or with the ZIP lookup.