Frost dates for 99346Plymouth, WA
The average last spring frost in Plymouth is March 27 and the average first fall frost is November 4, giving a typical growing season of about 221 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Mar 27
- Average first fall frost
- Nov 4
- Growing season
- 221 days
Safer after Apr 14 (1-in-10 risk)
Possible by Oct 21 (1-in-10 risk)
First frost typically in 3 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) | Mar 31 · Apr 15 · May 1 | Oct 9 · Oct 24 · Nov 7 | 187 days | 100% |
| Frost / freeze (32°F) | Mar 8 · Mar 27 · Apr 14 | Oct 21 · Nov 4 · Nov 22 | 221 days | 100% |
| Hard freeze (28°F) | Feb 14 · Mar 6 · Mar 28 | Oct 30 · Nov 18 · Dec 6 | 252 days | 100% |
Planting calendar for Plymouth
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 | Feb 24 – May 2 |
| Tomatoes | Transplant outdoors | Apr 12 – Jul 15 |
| Peppers | Start seeds indoors | Feb 24 – Mar 27 |
| Peppers | Transplant outdoors | Apr 26 – May 27 |
| Eggplant | Start seeds indoors | Mar 13 – Apr 11 |
| Eggplant | Transplant outdoors | Apr 26 – May 27 |
| Cucumbers | Sow outdoors | Apr 26 – Jul 25 |
| Summer squash | Sow outdoors | Apr 12 – May 27 |
| Winter squash & pumpkins | Sow outdoors | Apr 26 – May 27 |
| Snap beans | Sow outdoors | Apr 12 – Aug 17 |
| Sweet corn | Sow outdoors | Apr 12 – Jul 15 |
| Watermelon & cantaloupe | Sow outdoors | Apr 26 – May 27 |
| Okra | Sow outdoors | Apr 19 – May 12 |
| Peas | Sow outdoors (spring) | Feb 24 – Apr 11 |
| Potatoes | Plant outdoors (spring) | Feb 24 – Apr 26 |
| Onions | Start seeds indoors (spring) | Jan 13 – Feb 9 |
| Onions | Transplant outdoors (spring) | Mar 13 – Apr 11 |
| Broccoli | Start seeds indoors (spring) | Feb 6 – Mar 12 |
| Broccoli | Transplant outdoors (spring) | Mar 13 – Apr 11 |
| Broccoli | Start seeds indoors (fall) | Jul 5 – Jul 15 |
| Broccoli | Transplant outdoors (fall) | Aug 4 – Aug 15 |
| Cabbage | Start seeds indoors (spring) | Jan 27 – Feb 24 |
| Cabbage | Transplant outdoors (spring) | Feb 24 – Mar 27 |
| Cabbage | Start seeds indoors (fall) | Jun 25 – Jul 25 |
| Cabbage | Transplant outdoors (fall) | Jul 25 – Aug 25 |
| Leaf lettuce | Sow outdoors (spring) | Feb 24 – May 12 |
| Leaf lettuce | Sow outdoors (fall) | Jul 25 – Sep 10 |
| Spinach | Sow outdoors (spring) | Feb 17 – Apr 2 |
| Spinach | Sow outdoors (fall) | Aug 11 – Sep 15 |
| Radishes | Sow outdoors (spring) | Feb 24 – Apr 16 |
| Radishes | Sow outdoors (fall) | Jul 25 – Sep 25 |
| Kale | Sow outdoors (spring) | Mar 13 – Apr 2 |
| Kale | Sow outdoors (fall) | Jul 18 – Aug 25 |
| Carrots | Sow outdoors (spring) | Mar 27 – May 12 |
| Carrots | Sow outdoors (fall) | Jun 25 – Aug 10 |
| Garlic | Plant outdoors (fall) | Oct 25 – Nov 25 |
Where these dates come from
ZIP code 99346 is matched to the NOAA station Mcnary Dam, WA, 8.2 km away, at 361 ft elevation (59 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Mcnary Dam, WA (used) | 361 ft | Mar 27 | Nov 4 |
| Mcnary Dam #2, OR | 361 ft | Mar 30 | Nov 4 |
| Hermiston 2 Nw, OR | 460 ft | Apr 27 | Oct 7 |
| Hermiston Muni Ap, OR | 641 ft | Apr 26 | Oct 10 |
Frost dates near Plymouth
- Umatilla, OR 97882 · last Apr 27, first Oct 7
- Irrigon, OR 97844 · last Apr 14, first Oct 21
- Hermiston, OR 97838 · last Apr 27, first Oct 7
- Stanfield, OR 97875 · last Apr 26, first Oct 10
- Echo, OR 97826 · last Apr 26, first Oct 10
- Boardman, OR 97818 · last Apr 14, first Oct 21
- Kennewick, WA 99338 · last Mar 28, first Oct 30
- Paterson, WA 99345 · last Apr 14, first Oct 21
Frequently asked questions
- When is the last frost in Plymouth, WA?
- For ZIP code 99346, the average last spring frost (32°F) is March 27, based on NOAA 1991-2020 climate normals for the Mcnary Dam, WA weather station. There is a 1-in-10 chance of a frost after April 14.
- When is the first frost in Plymouth, WA?
- The average first fall frost (32°F) is November 4. There is a 1-in-10 chance of frost by October 21, so tender plants are at risk from that point on.
- How long is the growing season in 99346?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 221 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.