Frost Dates for Mercer Island, WA
In Mercer Island, WA, the average last spring frost is around Mar 13 and the average first fall frost around Nov 17, for a growing season of about 247 days. For frost-tender plants, wait until Apr 1, when the chance of frost drops to 10%.
Based on NOAA 1991–2020 records from the Seattle Boeing Fld, WA weather station, 4 miles away, elevation 20 ft. Frost can come earlier in low spots and valleys and later near cities and large lakes.
Frost probability by date
Chance of a 32°F frost after the spring date, or before the fall date.
| Chance | Last spring frost | First fall frost |
|---|---|---|
| 10% | Apr 1 | Nov 1 |
| 20% | Mar 25 | Nov 6 |
| 30% | Mar 21 | Nov 10 |
| 40% | Mar 17 | Nov 13 |
| 50% | Mar 13 | Nov 17 |
| 60% | Mar 9 | Nov 21 |
| 70% | Mar 4 | Nov 24 |
| 80% | Feb 28 | Nov 29 |
| 90% | Feb 20 | Dec 6 |
Light frost vs. hard freeze
Average (50%) dates for each temperature. Tender plants are damaged at 36°F; most hardy crops survive until 28°F.
| Temperature | Last in spring | First in fall |
|---|---|---|
| Light frost (36°F) | Apr 3 | Oct 31 |
| Frost / freeze (32°F) | Mar 13 | Nov 17 |
| Hard freeze (28°F) | Feb 18 | Dec 2 |
Planting calendar for Mercer Island
Transplant Mar 20 – Apr 3
Transplant Mar 27 – Apr 10
Transplant Mar 27 – Apr 10
Transplant Mar 20 – Apr 3
Sow or transplant Mar 20 – Apr 3
Sow or transplant Mar 20 – Apr 3
Sow or transplant Mar 27 – Apr 10
Sow or transplant Feb 13 – Feb 27
Fall sowing Sep 22 – Oct 20
Fall sowing Sep 22 – Oct 13
Fall sowing Sep 8 – Sep 22
Sow or transplant Feb 13 – Feb 27
Fall sowing Sep 8 – Oct 6
Transplant Feb 27 – Mar 13
Fall sowing Aug 25 – Sep 8
Transplant Feb 20 – Mar 6
Fall sowing Aug 25 – Sep 8
Fall sowing Aug 25 – Sep 8
Fall sowing Oct 6 – Oct 27
Fall sowing Sep 8 – Sep 22
Plant Feb 13 – Feb 27
Based on the average last frost (Mar 13) and first frost (Nov 17). The dashed lines mark those dates. Seed packets list days to maturity; adjust for your varieties.