Bryn Mawr-Skyway, WA planting zone & frost dates
Bryn Mawr-Skyway is in USDA hardiness zone 9a. The last spring frost usually comes around March 13 and the first fall frost around November 16, for a growing season of about 248 days.
Planting calendar for Bryn Mawr-Skyway
Dates are counted from the average last spring frost (March 13) 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 16 – Jan 30 Transplant outdoors: Mar 20 – Mar 27 |
| Peppers | Start seeds indoors: Jan 2 – Jan 16 Transplant outdoors: Mar 27 – Apr 3 |
| Eggplant | Start seeds indoors: Jan 2 – Jan 16 Transplant outdoors: Mar 27 – Apr 3 |
| Broccoli | Start seeds indoors: Jan 2 – Jan 16 Transplant outdoors: Feb 13 – Feb 27 |
| Cabbage | Start seeds indoors: Jan 2 – Jan 16 Transplant outdoors: Feb 13 – Feb 27 |
| Onions (sets) | Plant outdoors: Feb 13 – Feb 27 |
| Peas | Sow outdoors: Jan 30 – Feb 13 |
| Spinach | Sow outdoors: Jan 30 – Feb 13 |
| Lettuce | Sow outdoors: Feb 13 – Feb 27 |
| Carrots | Sow outdoors: Feb 13 – Feb 27 |
| Potatoes | Plant outdoors: Feb 13 – Feb 27 |
| Beans | Sow outdoors: Mar 20 – Mar 27 |
| Sweet corn | Sow outdoors: Mar 20 – Mar 27 |
| Cucumbers | Sow outdoors: Mar 20 – Mar 27 |
| Squash & zucchini | Sow outdoors: Mar 20 – Mar 27 |
| Basil | Start seeds indoors: Jan 30 – Feb 13 Transplant outdoors: Mar 20 – Mar 27 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Sep 21 (8 weeks before the average first fall frost on Nov 16).
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 19 | Mar 13 | Mar 31 |
| First 32°F frost in fall is before | Dec 9 | Nov 16 | Oct 29 |
How to read it: in spring there is a 10% chance of a frost after March 31, so that is a safe date for tender plants. In fall there is a 10% chance of frost before October 29. A hard freeze (28°F) usually ends around February 13.
Nearby cities
- Renton zone 9a, last frost Mar 13
- Tukwila zone 9a, last frost Mar 13
- SeaTac zone 9a, last frost Mar 2
- Columbia City zone 9a, last frost Mar 13
- Mercer Island zone 9a, last frost Mar 13
- Fairwood zone 8b, last frost Mar 13
- Newcastle zone 8b, last frost Mar 13
- East Hill-Meridian zone 8b, last frost Mar 20
Questions
What growing zone is Bryn Mawr-Skyway, WA?
Bryn Mawr-Skyway 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 Bryn Mawr-Skyway?
The average last spring frost (32°F) in Bryn Mawr-Skyway is March 13. There is still a 10% chance of frost until March 31.
When can I plant tomatoes in Bryn Mawr-Skyway?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around Mar 20 – Mar 27. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Renton Muni Ap, WA (USW00094248), 2.0 km (1.2 mi) from the city center, elevation 9 m, based on 19 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.