Thornton, WA frost dates
Last spring frostMay 7median date
First fall frostSep 28median date
Growing season144 daysfrost-free
Hardiness zone6bZone 6b
How Thornton compares
- In 8 years out of 10, the last spring frost in Thornton falls between April 22 and May 25, a 33-day window. The first fall frost falls between September 11 and October 16.
- The median last frost is 16 days later than the Washington median of Apr 21.
- Its 144-day growing season is longer than 13% of the 491 Washington places with a regular frost season (state median 182 days).
- The last frost is 15 days later than the zone 6b median of Apr 22. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 6b chart.
- The weather station records an average of 146 nights a year at or below 32°F.
- Compared with Spokane, WA, 60 km away, the last frost here is 11 days later than there and the growing season is 28 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 22 |
| 50% (median) | May 7 |
| 10% (safe for tender plants) | May 25 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 11 |
| 50% (median) | September 28 |
| 90% (late) | October 16 |
Frost here means 32°F (0°C). A median date means half of years have their last frost earlier and half later.
Planting calendar for Thornton, WA
Thornton, WA frost dates — last frost May 7, first frost Sep 28, zone 6b. whenisthelastfrost.com
Crop
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Start indoors: Feb 12 to Feb 26Transplant outside: Apr 9 to Apr 23
Start indoors: Feb 26 to Mar 12Transplant outside: May 21 to Jun 4
Start indoors: Feb 26 to Mar 12Transplant outside: May 21 to Jun 4
Start indoors: Mar 12 to Mar 26Transplant outside: May 14 to May 28
Start indoors: Mar 12 to Mar 26Transplant outside: Apr 16 to Apr 30Sow outdoors: Apr 9 to May 14Plant for fall: Aug 3 to Aug 31
Start indoors: Mar 12 to Mar 26Transplant outside: Apr 9 to Apr 23Sow outdoors: Apr 9 to Apr 23Plant for fall: Jul 20 to Aug 10
Start indoors: Mar 12 to Mar 26Transplant outside: Apr 23 to May 7Plant for fall: Jun 22 to Jul 13
Start indoors: Mar 12 to Mar 26Transplant outside: Apr 16 to Apr 30Plant for fall: Jun 22 to Jul 13
Start indoors: Mar 12 to Mar 26Transplant outside: Apr 23 to May 7Plant for fall: Jun 22 to Jul 13
Start indoors: Mar 26 to Apr 9Transplant outside: May 28 to Jun 11Sow outdoors: May 28 to Jun 11
Start indoors: Mar 26 to Apr 9Transplant outside: May 14 to May 28
Sow outdoors: Mar 26 to Apr 16Plant for fall: Jul 6 to Jul 27
Sow outdoors: Mar 26 to Apr 16Plant for fall: Aug 3 to Aug 24
Sow outdoors: Apr 2 to May 14Plant for fall: Aug 17 to Sep 7
Start indoors: Apr 9 to Apr 16Transplant outside: May 21 to May 28Sow outdoors: May 14 to May 28Plant for fall: Jul 13 to Jul 27
Start indoors: Apr 9 to Apr 16Sow outdoors: May 14 to May 28Plant for fall: Jul 20 to Aug 3
Start indoors: Apr 9 to Apr 16Sow outdoors: May 14 to May 28
Start indoors: Apr 9 to Apr 16Transplant outside: May 21 to Jun 4
Sow outdoors: Apr 16 to May 14Plant for fall: Jul 6 to Jul 20
Sow outdoors: Apr 16 to May 14Plant for fall: Jul 20 to Aug 3
Sow outdoors: Apr 16 to May 7
Sow outdoors: Apr 23 to May 21Plant for fall: Jul 20 to Aug 3
Sow outdoors: Apr 23 to May 14Plant for fall: Aug 3 to Aug 24
Sow outdoors: May 14 to Jun 4Plant for fall: Jul 13 to Jul 27
Sow outdoors: May 14 to May 28
Transplant outside: May 21 to Jun 11
Plant for fall: Sep 14 to Oct 19
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Thornton, WA
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 12 – Feb 26 | Apr 9 – Apr 23 | — | — |
| Peppers | Feb 26 – Mar 12 | May 21 – Jun 4 | — | — |
| Eggplant | Feb 26 – Mar 12 | May 21 – Jun 4 | — | — |
| Tomatoes | Mar 12 – Mar 26 | May 14 – May 28 | — | — |
| Lettuce | Mar 12 – Mar 26 | Apr 16 – Apr 30 | Apr 9 – May 14 | Aug 3 – Aug 31 |
| Kale | Mar 12 – Mar 26 | Apr 9 – Apr 23 | Apr 9 – Apr 23 | Jul 20 – Aug 10 |
| Broccoli | Mar 12 – Mar 26 | Apr 23 – May 7 | — | Jun 22 – Jul 13 |
| Cabbage | Mar 12 – Mar 26 | Apr 16 – Apr 30 | — | Jun 22 – Jul 13 |
| Cauliflower | Mar 12 – Mar 26 | Apr 23 – May 7 | — | Jun 22 – Jul 13 |
| Okra | Mar 26 – Apr 9 | May 28 – Jun 11 | May 28 – Jun 11 | — |
| Basil | Mar 26 – Apr 9 | May 14 – May 28 | — | — |
| Peas | — | — | Mar 26 – Apr 16 | Jul 6 – Jul 27 |
| Spinach | — | — | Mar 26 – Apr 16 | Aug 3 – Aug 24 |
| Radishes | — | — | Apr 2 – May 14 | Aug 17 – Sep 7 |
| Cucumbers | Apr 9 – Apr 16 | May 21 – May 28 | May 14 – May 28 | Jul 13 – Jul 27 |
| Zucchini & Summer Squash | Apr 9 – Apr 16 | — | May 14 – May 28 | Jul 20 – Aug 3 |
| Winter Squash & Pumpkins | Apr 9 – Apr 16 | — | May 14 – May 28 | — |
| Melons & Watermelon | Apr 9 – Apr 16 | May 21 – Jun 4 | — | — |
| Carrots | — | — | Apr 16 – May 14 | Jul 6 – Jul 20 |
| Beets | — | — | Apr 16 – May 14 | Jul 20 – Aug 3 |
| Potatoes | — | — | Apr 16 – May 7 | — |
| Swiss Chard | — | — | Apr 23 – May 21 | Jul 20 – Aug 3 |
| Cilantro | — | — | Apr 23 – May 14 | Aug 3 – Aug 24 |
| Green Beans | — | — | May 14 – Jun 4 | Jul 13 – Jul 27 |
| Sweet Corn | — | — | May 14 – May 28 | — |
| Sweet Potatoes | — | May 21 – Jun 11 | — | — |
| Garlic | — | — | — | Sep 14 – Oct 19 |
Dates come from the median frost dates and common extension-service timing. Adjust for your soil temperature, microclimate and the varieties you grow.
About these dates
Based on 1991–2020 NOAA climate normals for the Rosalia, WA weather station, 12 km away (elevation 2,421 ft (738 m)).
Frost dates near Thornton
- Oakesdale May 7 · Sep 28
- Rosalia May 7 · Sep 28
- Malden May 7 · Sep 28
- Steptoe Apr 29 · Oct 4
- Saint John Apr 29 · Oct 4
- Belmont May 7 · Sep 28
- Garfield May 15 · Sep 21
- Farmington May 15 · Sep 21
- Tekoa May 11 · Oct 5
- Latah May 11 · Oct 5
Frequently asked questions
When is the last frost in Thornton, WA?
The median last spring frost in Thornton, WA is May 7. There is still about a 10% chance of frost after May 25, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Thornton, WA?
The median first fall frost is September 28, with about a 10% chance of frost before September 11.
How long is the growing season in Thornton, WA?
About 144 days between the median last spring frost and first fall frost.
What planting zone is Thornton, WA?
Thornton, WA is in USDA hardiness zone 6b.