Best days to plant grass seed in Seattle, WA this week
Here's the next 7 days for seeding a lawn in Seattle, checked hour by hour against the published thresholds. Below it: what Seattle's 1991–2020 climate averages say about the months that usually work.
This week in Seattle
Asking the sky…
Fairsky is not a substitute for official warnings. For warnings, go to weather.gov. Verdicts are guidance, not guarantees. Your product's label always wins.
When seeding a lawn usually works in Seattle
- On 1991–2020 averages, Seattle has normal highs of 60–80°F with lows of 45°F or warmer in May–October, the air temperatures Fairsky looks for when seeding cool-season grass.
- October averages 2.0 days with half an inch of rain or more, the kind of downpour that can wash fresh seed around.
- The median first hard freeze (28°F) of fall comes around December 2; seed early enough that the grass is up and growing before then.
| Month | Avg high | Avg low | Days ≥0.10" rain | Days ≥0.50" rain | Highs 60–80°F, lows 45°F+ |
|---|---|---|---|---|---|
| January | 49° | 37° | 12.1 | 3.6 | – |
| February | 51° | 37° | 9.0 | 2.3 | – |
| March | 55° | 39° | 10.5 | 2.0 | – |
| April | 60° | 44° | 8.0 | 1.0 | – |
| May | 67° | 49° | 5.6 | 0.9 | Yes |
| June | 71° | 54° | 3.6 | 0.5 | Yes |
| July | 77° | 58° | 1.3 | 0.1 | Yes |
| August | 77° | 58° | 1.8 | 0.3 | Yes |
| September | 72° | 54° | 3.8 | 0.7 | Yes |
| October | 61° | 46° | 7.8 | 2.0 | Yes |
| November | 53° | 40° | 11.3 | 4.1 | – |
| December | 48° | 36° | 11.4 | 3.4 | – |
Station: Seattle Boeing Fld (NOAA NCEI USW00024234), about 9 km from central Seattle. “Rain days” count days with 0.10" or more of precipitation. “Highs 60–80°F, lows 45°F+” checks the monthly averages only; any given week can be warmer, colder or wetter.
The rules we check
- GO when estimated soil is 50–65°F and the next five days average highs of 60–80°F. (Fairsky default: no source gave a number)
- NO when estimated soil is under 45°F or a hard freeze (28°F or colder) is ahead. (Fairsky default: no source gave a number)
- Hold off when an inch or more of rain is due in the next 24 hours; it washes seed away. (Fairsky default: no source gave a number)
- Hot (soil above 70°F or highs above 85°F) means slow, stressed germination for cool-season grass.
- Wind under 20 mph while spreading. (Fairsky default: no source gave a number)
Your product's label always wins. Labels differ by product; in the app you can enter your label's temperature range and rain-free hours, and the verdict uses them instead.
Sources: Purdue Turf: optimum temperatures for seed germination
More home and yard jobs in Seattle
- Stain a deckDeck and fence stain: 50–90°F, dry wood, 24 rain-free hours after.
- Paint a house exteriorExterior latex paint: 40°F and up, 5°F above the dew point, 4 dry hours after.
- Pour concreteConcrete: 40–85°F, no rain for 24 hours, no freezing for 48.
- Spray weedsWeed killer: 3–10 mph wind, 45–85°F, 4 rain-free hours after.
- Apply pre-emergentCrabgrass pre-emergent: before soil holds 55°F (about 200 GDD), then water it in.
- Seal a drivewayAsphalt sealcoat: 55°F and rising, 50°F overnight, 36 rain-free hours.
- Cover plants for frostFrost watch: cover at 34°F, or 36°F on clear, calm nights; 28°F is a hard freeze.
The app covers 47 activities in all, from mowing to a round of golf: see every activity and its rules.
Plant grass seed in nearby cities
- Portland, OR145 miles away
- Spokane, WA228 miles away
- Boise, ID405 miles away
- Sacramento, CA625 miles away
- Stockton, CA669 miles away
- Ogden, UT674 miles away
All plant grass seed cities: Plant grass seed, by city · Home and yard in Washington
Questions
What's the best month to plant grass seed in Seattle?
On 1991–2020 averages, July usually fits best in Seattle. Any given week can still be wrong for it, which is what the live verdict above is for.
How is this verdict made?
We take the National Weather Service hourly forecast for Seattle and check each hour against the thresholds listed above. The result is guidance, not a guarantee; your product's label always wins.
When should I seed my lawn in Seattle?
Cool-season grass seed does best in mild weather with warm soil, usually early fall or spring. July is typically the best fit in Seattle.
Fairsky is not a substitute for official warnings. For warnings, go to weather.gov.
Live forecasts: National Weather Service / NOAA (public domain), fetched by your browser. Climate averages: NOAA NCEI U.S. Climate Normals, 1991–2020 (public domain). Activity thresholds: product data sheets, ACI and university extension guidance, linked on each page; your product’s label wins.