When to plant in Newcastle, WA
USDA Zone 8bNewcastle, Washington frost dates, USDA zone, and a full-year planting calendar, drawn from the nearest NOAA station and tuned to the local season.
A generous ~248-day season lets Newcastle gardeners direct-sow more and still ripen long-maturity crops like melons and winter squash. Zone 8b means many perennials and even some tender shrubs overwinter in Newcastle, while your frost dates still decide when annuals go out.
Frost probability
RENTON MUNI AP · 1991–2020The date the last spring and first fall frost occur, by threshold and probability. A 90% date is later in spring — and earlier in fall — than a 10% date; the 50% · 32°F row is what most gardeners plan around. These are Newcastle’s own odds, recorded at RENTON MUNI AP.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | Apr 25 | Apr 6 | Mar 21 | Oct 17 | Oct 31 | Nov 17 |
| 32°F | Mar 31 | Mar 13 | Feb 19 | Oct 29 | Nov 16 | Dec 9 |
| 28°F | Mar 6 | Feb 13 | Jan 1 | Nov 11 | Dec 6 | Jan 9 |
Download this table as CSV ↓ — every threshold and probability, plus this city’s planting-window dates.
What to plant now
TODAY · JULY 19Full-year planting calendar
Each bar is the exact window to take a planting action in Newcastle, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 14 km · complete 32°F normalsWhen stations disagree by more than a few days, that spread is real microclimate variation — elevation, water, urban heat. Judge which station best matches your own yard.
Newcastle planting FAQ
When is the last spring frost in Newcastle, WA?
Plan for the last spring frost in Newcastle around March 13 (the date it has a 50% chance of a 32°F freeze). Anything frost-sensitive should go out after it.
When is the first fall frost in Newcastle, WA?
Expect Newcastle's first fall frost near November 16 — a 50% chance of 32°F by that date. Bring in or cover tender crops ahead of it.
What hardiness zone is Newcastle in?
Newcastle is in USDA hardiness zone 8b. In zone 8b, winters are mild — many tender perennials overwinter here.
How long is the growing season in Newcastle?
There are roughly 248 frost-free days in Newcastle (a long growing season), running from the average last frost around March 13 to the first fall frost near November 16.
When should I plant tomatoes in Newcastle?
In Newcastle, start tomato seeds indoors around January 16–January 30, then transplant seedlings outdoors around March 20 once the danger of frost has passed.
Never miss a window in Newcastle
An email when it’s time to start seeds, transplant, and sow — timed to Newcastle’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Mercer Island · 6 km
- Renton · 6 km
- Bryn Mawr-Skyway · 7 km
- Bellevue · 7 km
- East Renton Highlands · 9 km
- Issaquah · 9 km
- Fairwood · 10 km
- Tukwila · 10 km
Frost dates recorded at RENTON MUNI AP, 6 km from the city center · 1991–2020 NOAA climate normals · zone from the USDA/PRISM 2023 map. How we compute this.
BlissGarden. "When to Plant in Newcastle, WA — Frost Dates & Zone 8b." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USW00094248. Retrieved from https://blissgarden.com/washington/newcastle.