Sumas, WA frost dates
Last spring frostApr 18median date
First fall frostOct 18median date
Growing season183 daysfrost-free
Hardiness zone8aZone 8a
How Sumas compares
- In 8 years out of 10, the last spring frost in Sumas falls between March 27 and May 5, a 39-day window. The first fall frost falls between September 28 and November 8.
- The median last frost is 3 days earlier than the Washington median of Apr 21.
- Its 183-day growing season is longer than 51% of the 491 Washington places with a regular frost season (state median 182 days).
- The last frost is 20 days later than the zone 8a median of Mar 29. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 8a chart.
- The weather station records an average of 57 nights a year at or below 32°F.
- Compared with Bellingham, WA, 31 km away, the last frost here is 17 days later than there and the growing season is 32 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | March 27 |
| 50% (median) | April 18 |
| 10% (safe for tender plants) | May 5 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 28 |
| 50% (median) | October 18 |
| 90% (late) | November 8 |
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 Sumas, WA
Sumas, WA frost dates — last frost Apr 18, first frost Oct 18, zone 8a. whenisthelastfrost.com
Crop
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Start indoors: Jan 24 to Feb 7Transplant outside: Mar 21 to Apr 4
Start indoors: Feb 7 to Feb 21Transplant outside: May 2 to May 16
Start indoors: Feb 7 to Feb 21Transplant outside: May 2 to May 16
Start indoors: Feb 21 to Mar 7Transplant outside: Apr 25 to May 9
Start indoors: Feb 21 to Mar 7Transplant outside: Mar 28 to Apr 11Sow outdoors: Mar 21 to Apr 25Plant for fall: Aug 23 to Sep 20
Start indoors: Feb 21 to Mar 7Transplant outside: Mar 21 to Apr 4Sow outdoors: Mar 21 to Apr 4Plant for fall: Aug 9 to Aug 30
Start indoors: Feb 21 to Mar 7Transplant outside: Apr 4 to Apr 18Plant for fall: Jul 12 to Aug 2
Start indoors: Feb 21 to Mar 7Transplant outside: Mar 28 to Apr 11Plant for fall: Jul 12 to Aug 2
Start indoors: Feb 21 to Mar 7Transplant outside: Apr 4 to Apr 18Plant for fall: Jul 12 to Aug 2
Start indoors: Mar 7 to Mar 21Transplant outside: May 9 to May 23Sow outdoors: May 9 to May 23
Start indoors: Mar 7 to Mar 21Transplant outside: Apr 25 to May 9
Sow outdoors: Mar 7 to Mar 28Plant for fall: Jul 26 to Aug 16
Sow outdoors: Mar 7 to Mar 28Plant for fall: Aug 23 to Sep 13
Sow outdoors: Mar 14 to Apr 25Plant for fall: Sep 6 to Sep 27
Start indoors: Mar 21 to Mar 28Transplant outside: May 2 to May 9Sow outdoors: Apr 25 to May 9Plant for fall: Aug 2 to Aug 16
Start indoors: Mar 21 to Mar 28Sow outdoors: Apr 25 to May 9Plant for fall: Aug 9 to Aug 23
Start indoors: Mar 21 to Mar 28Sow outdoors: Apr 25 to May 9
Start indoors: Mar 21 to Mar 28Transplant outside: May 2 to May 16
Sow outdoors: Mar 28 to Apr 25Plant for fall: Jul 26 to Aug 9
Sow outdoors: Mar 28 to Apr 25Plant for fall: Aug 9 to Aug 23
Sow outdoors: Mar 28 to Apr 18
Sow outdoors: Apr 4 to May 2Plant for fall: Aug 9 to Aug 23
Sow outdoors: Apr 4 to Apr 25Plant for fall: Aug 23 to Sep 13
Sow outdoors: Apr 25 to May 16Plant for fall: Aug 2 to Aug 16
Sow outdoors: Apr 25 to May 9
Transplant outside: May 2 to May 23
Plant for fall: Oct 4 to Nov 8
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Sumas, WA
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Jan 24 – Feb 7 | Mar 21 – Apr 4 | — | — |
| Peppers | Feb 7 – Feb 21 | May 2 – May 16 | — | — |
| Eggplant | Feb 7 – Feb 21 | May 2 – May 16 | — | — |
| Tomatoes | Feb 21 – Mar 7 | Apr 25 – May 9 | — | — |
| Lettuce | Feb 21 – Mar 7 | Mar 28 – Apr 11 | Mar 21 – Apr 25 | Aug 23 – Sep 20 |
| Kale | Feb 21 – Mar 7 | Mar 21 – Apr 4 | Mar 21 – Apr 4 | Aug 9 – Aug 30 |
| Broccoli | Feb 21 – Mar 7 | Apr 4 – Apr 18 | — | Jul 12 – Aug 2 |
| Cabbage | Feb 21 – Mar 7 | Mar 28 – Apr 11 | — | Jul 12 – Aug 2 |
| Cauliflower | Feb 21 – Mar 7 | Apr 4 – Apr 18 | — | Jul 12 – Aug 2 |
| Okra | Mar 7 – Mar 21 | May 9 – May 23 | May 9 – May 23 | — |
| Basil | Mar 7 – Mar 21 | Apr 25 – May 9 | — | — |
| Peas | — | — | Mar 7 – Mar 28 | Jul 26 – Aug 16 |
| Spinach | — | — | Mar 7 – Mar 28 | Aug 23 – Sep 13 |
| Radishes | — | — | Mar 14 – Apr 25 | Sep 6 – Sep 27 |
| Cucumbers | Mar 21 – Mar 28 | May 2 – May 9 | Apr 25 – May 9 | Aug 2 – Aug 16 |
| Zucchini & Summer Squash | Mar 21 – Mar 28 | — | Apr 25 – May 9 | Aug 9 – Aug 23 |
| Winter Squash & Pumpkins | Mar 21 – Mar 28 | — | Apr 25 – May 9 | — |
| Melons & Watermelon | Mar 21 – Mar 28 | May 2 – May 16 | — | — |
| Carrots | — | — | Mar 28 – Apr 25 | Jul 26 – Aug 9 |
| Beets | — | — | Mar 28 – Apr 25 | Aug 9 – Aug 23 |
| Potatoes | — | — | Mar 28 – Apr 18 | — |
| Swiss Chard | — | — | Apr 4 – May 2 | Aug 9 – Aug 23 |
| Cilantro | — | — | Apr 4 – Apr 25 | Aug 23 – Sep 13 |
| Green Beans | — | — | Apr 25 – May 16 | Aug 2 – Aug 16 |
| Sweet Corn | — | — | Apr 25 – May 9 | — |
| Sweet Potatoes | — | May 2 – May 23 | — | — |
| Garlic | — | — | — | Oct 4 – Nov 8 |
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 Clearbrook, WA weather station, 9 km away (elevation 66 ft (20 m)).
Frost dates near Sumas
- Maple Falls Apr 18 · Oct 18
- Nooksack Apr 18 · Oct 18
- Everson Apr 18 · Oct 18
- Lynden Apr 18 · Oct 18
- Deming Apr 18 · Oct 18
- Custer Mar 31 · Nov 4
- Bellingham Apr 1 · Nov 2
- Ferndale Mar 31 · Oct 30
- Acme Mar 27 · Nov 6
- Blaine Mar 31 · Nov 4
Frequently asked questions
When is the last frost in Sumas, WA?
The median last spring frost in Sumas, WA is April 18. There is still about a 10% chance of frost after May 5, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Sumas, WA?
The median first fall frost is October 18, with about a 10% chance of frost before September 28.
How long is the growing season in Sumas, WA?
About 183 days between the median last spring frost and first fall frost.
What planting zone is Sumas, WA?
Sumas, WA is in USDA hardiness zone 8a.