Frost Dates for Seattle, WA 98158

Seattle has 38 ZIP codes. The Seattle, WA frost page lists all of them with their dates.

Last spring frost April 10 · First fall frost October 25 · 198 frost-free days · USDA Zone 9a

Frost probability for 98158

Frost10%50%90%
Spring (last frost)May 6April 10March 14
Fall (first frost)October 2October 25November 17

Dates come from NOAA 1971–2000 freeze probabilities at the nearest reporting station (6.1 km away); the 50% date is the median year.

Month by month in Seattle

MonthWhat to do
JanuaryPlan your garden layout and order seeds. Research varieties suited to your frost dates.
FebruaryStart peppers and eggplant indoors 8–10 weeks before your last frost (around April 10). Start tomatoes about two weeks later, 6–8 weeks before last frost.
MarchStart herbs, basil, and squash indoors (4–6 weeks before frost). Direct sow peas, spinach, and lettuce if soil is workable.
AprilLast frost around April 10. Transplant cold-hardy crops (broccoli, kale, cabbage). Harden off tomato and pepper seedlings.
MayFrost has passed. Transplant tomatoes, peppers, and basil outdoors. Direct sow beans, cucumbers, squash, and zucchini.
JuneSuccession plant lettuce and greens. Keep beds weeded and watered consistently.
JulyHarvest regularly to encourage production. Monitor for pests and disease.
AugustMidsummer: harvest beans, zucchini, cucumbers. Start brassica seeds indoors for fall.
SeptemberFirst fall frost approaching (around October 25). Transplant fall brassicas. Sow spinach, arugula, and radishes.
OctoberFirst frost around October 25. Harvest tomatoes and peppers before frost. Cover cold-hardy crops with row covers to extend the season.
NovemberHarvest remaining cold-hardy crops: kale, carrots, and beets. Plant garlic bulbs for next year.
DecemberClean up spent plants. Add compost to beds. Rest, review, and plan next year's garden.

What grows in a 198-day season

Frequently Asked Questions

What is the last frost date for Seattle, WA (ZIP 98158)?

The median last spring frost date for Seattle, WA (ZIP code 98158) is around April 10. This is the 50th-percentile date — meaning half of all years see frost end before this date. Use the 10% and 90% dates to understand the full range of risk in your area.

What is the first fall frost date in Seattle, WA?

The median first fall frost date for Seattle, WA is around October 25. Plan to harvest or protect frost-sensitive crops like tomatoes and peppers at least a week before this date to avoid losses.

How long is the growing season in Seattle, WA?

The frost-free growing season in Seattle is about 198 days. This window — from your last spring frost to your first fall frost — is when warm-season vegetables thrive. Cold-hardy crops like kale, spinach, and peas can extend your season by weeks on either side.

What USDA hardiness zone is Seattle, WA?

Based on frost date patterns, Seattle falls approximately in 9a. USDA hardiness zones are determined by average annual minimum winter temperatures and guide both plant selection and planting timing for your location.

When should I start tomatoes indoors in Seattle, WA?

Start tomato seeds indoors 6–8 weeks before your last frost date (around April 10). For Seattle, that's roughly February 14 to February 28. Transplant outdoors 1–2 weeks after your last frost.

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