Frost dates for 83853Porthill, ID
The average last spring frost in Porthill is May 4 and the average first fall frost is September 30, giving a typical growing season of about 145 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 4
- Average first fall frost
- Sep 30
- Growing season
- 145 days
Safer after May 28 (1-in-10 risk)
Possible by Sep 10 (1-in-10 risk)
Last frost typically in 189 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) | May 3 · May 21 · Jun 8 | Aug 30 · Sep 16 · Oct 1 | 117 days | 100% |
| Frost / freeze (32°F) | Apr 20 · May 4 · May 28 | Sep 10 · Sep 30 · Oct 14 | 145 days | 100% |
| Hard freeze (28°F) | Mar 28 · Apr 16 · May 6 | Sep 24 · Oct 11 · Oct 27 | 175 days | 100% |
Planting calendar for Porthill
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 | Apr 3 – Jun 9 |
| Tomatoes | Transplant outdoors | May 20 – Jun 10 |
| Peppers | Start seeds indoors | Apr 3 – May 4 |
| Peppers | Transplant outdoors | Jun 3 – Jul 4 |
| Eggplant | Start seeds indoors | Apr 20 – May 19 |
| Eggplant | Transplant outdoors | Jun 3 – Jul 4 |
| Cucumbers | Sow outdoors | Jun 3 – Jun 20 |
| Summer squash | Sow outdoors | May 20 – Jul 4 |
| Winter squash & pumpkins | Sow outdoors | Jun 3 – Jul 4 |
| Snap beans | Sow outdoors | May 20 – Jul 13 |
| Sweet corn | Sow outdoors | May 20 – Jun 10 |
| Watermelon & cantaloupe | Sow outdoors | Jun 3 – Jul 4 |
| Okra | Sow outdoors | May 27 – Jun 19 |
| Peas | Sow outdoors (spring) | Apr 3 – May 19 |
| Potatoes | Plant outdoors (spring) | Apr 3 – Jun 3 |
| Onions | Start seeds indoors (spring) | Feb 20 – Mar 19 |
| Onions | Transplant outdoors (spring) | Apr 20 – May 19 |
| Broccoli | Start seeds indoors (spring) | Mar 16 – Apr 19 |
| Broccoli | Transplant outdoors (spring) | Apr 20 – May 19 |
| Broccoli | Start seeds indoors (fall) | May 31 – Jun 10 |
| Broccoli | Transplant outdoors (fall) | Jun 30 – Jul 11 |
| Cabbage | Start seeds indoors (spring) | Mar 6 – Apr 3 |
| Cabbage | Transplant outdoors (spring) | Apr 3 – May 4 |
| Cabbage | Start seeds indoors (fall) | May 21 – Jun 20 |
| Cabbage | Transplant outdoors (fall) | Jun 20 – Jul 21 |
| Leaf lettuce | Sow outdoors (spring) | Apr 3 – Jun 19 |
| Leaf lettuce | Sow outdoors (fall) | Jun 20 – Aug 6 |
| Spinach | Sow outdoors (spring) | Mar 27 – May 10 |
| Spinach | Sow outdoors (fall) | Jul 7 – Aug 11 |
| Radishes | Sow outdoors (spring) | Apr 3 – May 24 |
| Radishes | Sow outdoors (fall) | Jun 20 – Aug 21 |
| Kale | Sow outdoors (spring) | Apr 20 – May 10 |
| Kale | Sow outdoors (fall) | Jun 13 – Jul 21 |
| Carrots | Sow outdoors (spring) | May 4 – Jun 19 |
| Carrots | Sow outdoors (fall) | May 21 – Jul 6 |
| Garlic | Plant outdoors (fall) | Sep 20 – Oct 21 |
Where these dates come from
ZIP code 83853 is matched to the NOAA station Porthill 1 Sw, ID, 1.8 km away, at 1,799 ft elevation (458 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Porthill 1 Sw, ID (used) | 1,799 ft | May 4 | Sep 30 |
| Bonners Ferry, ID | 2,075 ft | Apr 30 | Oct 4 |
| Yaak 9Nne, MT | 3,085 ft | — | — |
| Boundary Dam, WA | 1,837 ft | May 4 | Oct 4 |
Frost dates near Porthill
- Eastport, ID 83826 · last Apr 30, first Oct 4
- Bonners Ferry, ID 83805 · last Apr 30, first Oct 4
- Moyie Springs, ID 83845 · last Apr 30, first Oct 4
- Naples, ID 83847 · last Apr 30, first Oct 4
- Nordman, ID 83848 · last May 20, first Sep 13
- Coolin, ID 83821 · last May 20, first Sep 13
- Metaline Falls, WA 99153 · last May 4, first Oct 4
- Metaline, WA 99152 · last May 4, first Oct 4
Frequently asked questions
- When is the last frost in Porthill, ID?
- For ZIP code 83853, the average last spring frost (32°F) is May 4, based on NOAA 1991-2020 climate normals for the Porthill 1 Sw, ID weather station. There is a 1-in-10 chance of a frost after May 28.
- When is the first frost in Porthill, ID?
- The average first fall frost (32°F) is September 30. There is a 1-in-10 chance of frost by September 10, so tender plants are at risk from that point on.
- How long is the growing season in 83853?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 145 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.