Frost dates for 83799Boise, ID
The average last spring frost in Boise is April 24 and the average first fall frost is October 21, giving a typical growing season of about 179 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 24
- Average first fall frost
- Oct 21
- Growing season
- 179 days
Safer after May 9 (1-in-10 risk)
Possible by Oct 5 (1-in-10 risk)
First frost typically in 4 days
Frost risk by date
NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.
| Temperature | Last spring: 90% / 50% / 10% chance | First fall: 10% / 50% / 90% chance | Growing season (50%) | Years with at least one |
|---|---|---|---|---|
| Light frost (36°F) | Apr 23 · May 8 · May 29 | Sep 25 · Oct 8 · Oct 25 | 153 days | 100% |
| Frost / freeze (32°F) | Apr 4 · Apr 24 · May 9 | Oct 5 · Oct 21 · Nov 5 | 179 days | 100% |
| Hard freeze (28°F) | Mar 10 · Apr 2 · Apr 25 | Oct 17 · Oct 31 · Nov 19 | 212 days | 100% |
Planting calendar for Boise
Planting windows from the University of Maryland Extension calendar, shifted to your average frost dates. Use them as a starting point and adjust for seed packet instructions and local conditions.
| Crop | Task | Window |
|---|---|---|
| Tomatoes | Start seeds indoors | Mar 24 – May 30 |
| Tomatoes | Transplant outdoors | May 10 – Jul 1 |
| Peppers | Start seeds indoors | Mar 24 – Apr 24 |
| Peppers | Transplant outdoors | May 24 – Jun 24 |
| Eggplant | Start seeds indoors | Apr 10 – May 9 |
| Eggplant | Transplant outdoors | May 24 – Jun 24 |
| Cucumbers | Sow outdoors | May 24 – Jul 11 |
| Summer squash | Sow outdoors | May 10 – Jun 24 |
| Winter squash & pumpkins | Sow outdoors | May 24 – Jun 24 |
| Snap beans | Sow outdoors | May 10 – Aug 3 |
| Sweet corn | Sow outdoors | May 10 – Jul 1 |
| Watermelon & cantaloupe | Sow outdoors | May 24 – Jun 24 |
| Okra | Sow outdoors | May 17 – Jun 9 |
| Peas | Sow outdoors (spring) | Mar 24 – May 9 |
| Potatoes | Plant outdoors (spring) | Mar 24 – May 24 |
| Onions | Start seeds indoors (spring) | Feb 10 – Mar 9 |
| Onions | Transplant outdoors (spring) | Apr 10 – May 9 |
| Broccoli | Start seeds indoors (spring) | Mar 6 – Apr 9 |
| Broccoli | Transplant outdoors (spring) | Apr 10 – May 9 |
| Broccoli | Start seeds indoors (fall) | Jun 21 – Jul 1 |
| Broccoli | Transplant outdoors (fall) | Jul 21 – Aug 1 |
| Cabbage | Start seeds indoors (spring) | Feb 24 – Mar 24 |
| Cabbage | Transplant outdoors (spring) | Mar 24 – Apr 24 |
| Cabbage | Start seeds indoors (fall) | Jun 11 – Jul 11 |
| Cabbage | Transplant outdoors (fall) | Jul 11 – Aug 11 |
| Leaf lettuce | Sow outdoors (spring) | Mar 24 – Jun 9 |
| Leaf lettuce | Sow outdoors (fall) | Jul 11 – Aug 27 |
| Spinach | Sow outdoors (spring) | Mar 17 – Apr 30 |
| Spinach | Sow outdoors (fall) | Jul 28 – Sep 1 |
| Radishes | Sow outdoors (spring) | Mar 24 – May 14 |
| Radishes | Sow outdoors (fall) | Jul 11 – Sep 11 |
| Kale | Sow outdoors (spring) | Apr 10 – Apr 30 |
| Kale | Sow outdoors (fall) | Jul 4 – Aug 11 |
| Carrots | Sow outdoors (spring) | Apr 24 – Jun 9 |
| Carrots | Sow outdoors (fall) | Jun 11 – Jul 27 |
| Garlic | Plant outdoors (fall) | Oct 11 – Nov 11 |
Where these dates come from
ZIP code 83799 is matched to the NOAA station Boise Air Terminal, ID, 6 km away, at 2,814 ft elevation (114 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Boise Air Terminal, ID (used) | 2,814 ft | Apr 24 | Oct 21 |
| Boise 7 N, ID | 3,885 ft | May 17 | Oct 12 |
| Boise Lucky Peak Dam, ID | 2,840 ft | Apr 30 | Oct 22 |
| Arrowrock Dam, ID | 3,235 ft | Apr 28 | Oct 14 |
Frost dates near Boise
- Boise, ID 83707 · last Apr 24, first Oct 21
- Garden City, ID 83714 · last Apr 24, first Oct 21
- Meridian, ID 83680 · last Apr 29, first Oct 13
- Eagle, ID 83616 · last Apr 29, first Oct 13
- Kuna, ID 83634 · last Apr 24, first Oct 21
- Mountain Home Afb, ID 83648 · last Apr 30, first Oct 17
- Star, ID 83669 · last Apr 29, first Oct 13
- Nampa, ID 83687 · last Apr 29, first Oct 13
Frequently asked questions
- When is the last frost in Boise, ID?
- For ZIP code 83799, the average last spring frost (32°F) is April 24, based on NOAA 1991-2020 climate normals for the Boise Air Terminal, ID weather station. There is a 1-in-10 chance of a frost after May 9.
- When is the first frost in Boise, ID?
- The average first fall frost (32°F) is October 21. There is a 1-in-10 chance of frost by October 5, so tender plants are at risk from that point on.
- How long is the growing season in 83799?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 179 days long.
- Are these frost dates a forecast?
- No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.