SeaTac, WA planting zone & frost dates
SeaTac is in USDA hardiness zone 9a. The last spring frost usually comes around March 2 and the first fall frost around November 23, for a growing season of about 266 days.
Planting calendar for SeaTac
Dates are counted from the average last spring frost (March 2) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.
| Crop | When |
|---|---|
| Tomatoes | Start seeds indoors: Jan 5 – Jan 19 Transplant outdoors: Mar 9 – Mar 16 |
| Peppers | Start seeds indoors: Dec 22 – Jan 5 Transplant outdoors: Mar 16 – Mar 23 |
| Eggplant | Start seeds indoors: Dec 22 – Jan 5 Transplant outdoors: Mar 16 – Mar 23 |
| Broccoli | Start seeds indoors: Dec 22 – Jan 5 Transplant outdoors: Feb 2 – Feb 16 |
| Cabbage | Start seeds indoors: Dec 22 – Jan 5 Transplant outdoors: Feb 2 – Feb 16 |
| Onions (sets) | Plant outdoors: Feb 2 – Feb 16 |
| Peas | Sow outdoors: Jan 19 – Feb 2 |
| Spinach | Sow outdoors: Jan 19 – Feb 2 |
| Lettuce | Sow outdoors: Feb 2 – Feb 16 |
| Carrots | Sow outdoors: Feb 2 – Feb 16 |
| Potatoes | Plant outdoors: Feb 2 – Feb 16 |
| Beans | Sow outdoors: Mar 9 – Mar 16 |
| Sweet corn | Sow outdoors: Mar 9 – Mar 16 |
| Cucumbers | Sow outdoors: Mar 9 – Mar 16 |
| Squash & zucchini | Sow outdoors: Mar 9 – Mar 16 |
| Basil | Start seeds indoors: Jan 19 – Feb 2 Transplant outdoors: Mar 9 – Mar 16 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Sep 28 (8 weeks before the average first fall frost on Nov 23).
Useful for zone 9a gardens
- Seed starting kit with dome — to start seeds indoors before the last frost
- LED grow light for seedlings — stops leggy seedlings
- Frost cloth / plant covers — for late spring and early fall frosts
- Soil thermometer — warm-season crops need soil above 60°F
- Shade cloth — for hot summers
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Frost risk in detail
| 90% chance | 50% chance | 10% chance | |
|---|---|---|---|
| Last 32°F frost in spring is after | Feb 5 | Mar 2 | Mar 23 |
| First 32°F frost in fall is before | Dec 15 | Nov 23 | Nov 6 |
How to read it: in spring there is a 10% chance of a frost after March 23, so that is a safe date for tender plants. In fall there is a 10% chance of frost before November 6. A hard freeze (28°F) usually ends around February 4.
Nearby cities
- Tukwila zone 9a, last frost Mar 13
- Des Moines zone 9a, last frost Mar 2
- Burien zone 9a, last frost Mar 2
- Bryn Mawr-Skyway zone 9a, last frost Mar 13
- Renton zone 9a, last frost Mar 13
- Kent zone 8b, last frost Mar 20
- White Center zone 9a, last frost Mar 13
- Lakeland North zone 8b, last frost Mar 20
Questions
What growing zone is SeaTac, WA?
SeaTac is in USDA Plant Hardiness Zone 9a (average extreme winter low 20°F to 25°F), according to the USDA 2023 map.
When is the last frost in SeaTac?
The average last spring frost (32°F) in SeaTac is March 2. There is still a 10% chance of frost until March 23.
When can I plant tomatoes in SeaTac?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around Mar 9 – Mar 16. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Seattle Tacoma Intl Ap, WA (USW00024233), 1.7 km (1.1 mi) from the city center, elevation 113 m, based on 26 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.