Newcastle, WA planting zone & frost dates
Newcastle is in USDA hardiness zone 8b. 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 Newcastle
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 8b 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
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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
- West Lake Sammamish zone 8b, last frost Mar 13
- East Renton Highlands zone 8b, last frost Mar 13
- Mercer Island zone 9a, last frost Mar 13
- Renton zone 9a, last frost Mar 13
- Bellevue zone 9a, last frost Mar 8
- Fairwood zone 8b, last frost Mar 13
- Bryn Mawr-Skyway zone 9a, last frost Mar 13
- Columbia City zone 9a, last frost Mar 13
Questions
What growing zone is Newcastle, WA?
Newcastle is in USDA Plant Hardiness Zone 8b (average extreme winter low 15°F to 20°F), according to the USDA 2023 map.
When is the last frost in Newcastle?
The average last spring frost (32°F) in Newcastle is March 13. There is still a 10% chance of frost until March 31.
When can I plant tomatoes in Newcastle?
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), 6.7 km (4.2 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.