Frost dates for 98010Black Diamond, WA
The average last spring frost in Black Diamond is April 20 and the average first fall frost is October 25, giving a typical growing season of about 187 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 20
- Average first fall frost
- Oct 25
- Growing season
- 187 days
Safer after May 10 (1-in-10 risk)
Possible by Oct 5 (1-in-10 risk)
Last frost typically in 170 days
Frost risk by date
NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.
| Temperature | Last spring: 90% / 50% / 10% chance | First fall: 10% / 50% / 90% chance | Growing season (50%) | Years with at least one |
|---|---|---|---|---|
| Light frost (36°F) | Apr 23 · May 10 · Jun 7 | Sep 19 · Oct 6 · Oct 26 | 146 days | 100% |
| Frost / freeze (32°F) | Mar 31 · Apr 20 · May 10 | Oct 5 · Oct 25 · Nov 12 | 187 days | 100% |
| Hard freeze (28°F) | Feb 28 · Mar 24 · Apr 16 | Oct 24 · Nov 12 · Dec 8 | 233 days | 100% |
Planting calendar for Black Diamond
Planting windows from the University of Maryland Extension calendar, shifted to your average frost dates. Use them as a starting point and adjust for seed packet instructions and local conditions.
| Crop | Task | Window |
|---|---|---|
| Tomatoes | Start seeds indoors | Mar 20 – May 26 |
| Tomatoes | Transplant outdoors | May 6 – Jul 5 |
| Peppers | Start seeds indoors | Mar 20 – Apr 20 |
| Peppers | Transplant outdoors | May 20 – Jun 20 |
| Eggplant | Start seeds indoors | Apr 6 – May 5 |
| Eggplant | Transplant outdoors | May 20 – Jun 20 |
| Cucumbers | Sow outdoors | May 20 – Jul 15 |
| Summer squash | Sow outdoors | May 6 – Jun 20 |
| Winter squash & pumpkins | Sow outdoors | May 20 – Jun 20 |
| Snap beans | Sow outdoors | May 6 – Aug 7 |
| Sweet corn | Sow outdoors | May 6 – Jul 5 |
| Watermelon & cantaloupe | Sow outdoors | May 20 – Jun 20 |
| Okra | Sow outdoors | May 13 – Jun 5 |
| Peas | Sow outdoors (spring) | Mar 20 – May 5 |
| Potatoes | Plant outdoors (spring) | Mar 20 – May 20 |
| Onions | Start seeds indoors (spring) | Feb 6 – Mar 5 |
| Onions | Transplant outdoors (spring) | Apr 6 – May 5 |
| Broccoli | Start seeds indoors (spring) | Mar 2 – Apr 5 |
| Broccoli | Transplant outdoors (spring) | Apr 6 – May 5 |
| Broccoli | Start seeds indoors (fall) | Jun 25 – Jul 5 |
| Broccoli | Transplant outdoors (fall) | Jul 25 – Aug 5 |
| Cabbage | Start seeds indoors (spring) | Feb 20 – Mar 20 |
| Cabbage | Transplant outdoors (spring) | Mar 20 – Apr 20 |
| Cabbage | Start seeds indoors (fall) | Jun 15 – Jul 15 |
| Cabbage | Transplant outdoors (fall) | Jul 15 – Aug 15 |
| Leaf lettuce | Sow outdoors (spring) | Mar 20 – Jun 5 |
| Leaf lettuce | Sow outdoors (fall) | Jul 15 – Aug 31 |
| Spinach | Sow outdoors (spring) | Mar 13 – Apr 26 |
| Spinach | Sow outdoors (fall) | Aug 1 – Sep 5 |
| Radishes | Sow outdoors (spring) | Mar 20 – May 10 |
| Radishes | Sow outdoors (fall) | Jul 15 – Sep 15 |
| Kale | Sow outdoors (spring) | Apr 6 – Apr 26 |
| Kale | Sow outdoors (fall) | Jul 8 – Aug 15 |
| Carrots | Sow outdoors (spring) | Apr 20 – Jun 5 |
| Carrots | Sow outdoors (fall) | Jun 15 – Jul 31 |
| Garlic | Plant outdoors (fall) | Oct 15 – Nov 15 |
Where these dates come from
ZIP code 98010 is matched to the NOAA station Landsburg, WA, 8 km away, at 535 ft elevation (118 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Landsburg, WA (used) | 535 ft | Apr 20 | Oct 25 |
| Palmer 3 Ese, WA | 920 ft | Apr 3 | Nov 11 |
| Buckley 1 Ne, WA | 685 ft | Apr 7 | Oct 30 |
| Mud Mtn Dam, WA | 1,308 ft | Apr 18 | Oct 31 |
Frost dates near Black Diamond
- Enumclaw, WA 98022 · last Apr 20, first Oct 25
- Auburn, WA 98092 · last Apr 20, first Oct 25
- Federal Way, WA 98093 · last Apr 20, first Oct 25
- Maple Valley, WA 98038 · last Apr 20, first Oct 25
- Ravensdale, WA 98051 · last Apr 3, first Nov 11
- Kent, WA 98042 · last Apr 20, first Oct 25
- Hobart, WA 98025 · last Apr 20, first Oct 25
- Renton, WA 98058 · last Apr 20, first Oct 25
Frequently asked questions
- When is the last frost in Black Diamond, WA?
- For ZIP code 98010, the average last spring frost (32°F) is April 20, based on NOAA 1991-2020 climate normals for the Landsburg, WA weather station. There is a 1-in-10 chance of a frost after May 10.
- When is the first frost in Black Diamond, WA?
- The average first fall frost (32°F) is October 25. There is a 1-in-10 chance of frost by October 5, so tender plants are at risk from that point on.
- How long is the growing season in 98010?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 187 days long.
- Are these frost dates a forecast?
- No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.