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ZIP 98101 planting calendar

When to plant watermelon in Seattle, WA - Zone 9a

In ZIP 98101, plant watermelon around Apr 3; this uses the Seattle frost station, USDA zone 9a, and watermelon timing rules.

Your Seattle calendar has a 245-day estimated frost-free season. This estimate uses the representative Seattle frost station, USDA zone 9a, and watermelon timing rules.

Source: seattle-tacoma frost station, USDA zone 9a, last updated 2026-06-28. Verify locally before planting high-value crops because microclimates, current weather, and yard exposure can move the safe date.

Reviewed by GrowZone Editorial. Calculated from the seattle-tacoma frost station and USDA zone 9a, last updated 2026-06-28.

In the Seattle area, watermelon timing follows the Seattle frost window, so the local ZIP date can differ from a broad zone-only calendar.

USDA zone 9a Seattle frost station Washington State University Extension Updated 2026-06-28
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Answer first

When to start watermelon seeds indoors in Seattle

In ZIP 98101, start watermelon seeds indoors around Feb 27, about 21 days before the Mar 20 last-frost estimate.

Start watermelon seeds indoors in Seattle around Feb 27, about 21 days before the Mar 20 last-frost estimate.

Seed starting schedule

Watermelon dates for Seattle, WA

StepDateHow to use it
Start IndoorsFebruary 27, 2026Start seeds under lights or in a bright indoor seed-starting space.
Transplant OutdoorsApril 3, 2026Move hardened-off seedlings outside after the frost-risk window.
Direct SowApril 3, 2026Sow seed outside when the crop and soil can handle the window.

Last frost

When is the last frost in Seattle?

Seattle (ZIP 98101) has an average last spring frost around Mar 20.

First frost

When is the first frost in Seattle?

The average first fall frost is around Nov 20, giving about 245 frost-free days.

Season map

Watermelon windows by month

JanFebMarAprMayJunJulAugSepOctNovDec
Start indoors
Feb 27
Direct sow
Apr 3
Transplant
Apr 3
Harvest
Jul 2
Frost watch
Aug 22

Reminder workflow

Every date has a next action

Start watermelon indoorsFeb 27
Last frost windowMar 20
Direct sow watermelonApr 3
Transplant watermelonApr 3
First watermelon harvest windowJul 2
Last watermelon sowing targetAug 22
SignalValueWhy it matters
Last frost estimateMarch 20, 2026Warm-season transplant risk starts falling after this window.
First frost estimateNovember 20, 2026Fall planting counts backward from this date.
Season length245 daysLonger seasons can support succession crops.
Spacing36-60 inAirflow and root space affect yield.
Soil temperature70 F+Seeds and transplants stall in cold soil.

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Local data

Why this date changes by ZIP

Seattle frost history and USDA zone 9a shift the safe planting window. GrowZone uses a local representative station instead of one national rule.

Washington State University Extension is the kind of local source to verify against when a crop is expensive, weather is unusual, or your yard has a cold pocket.

Crop note

Watermelon timing notes

Wait for warm soil; watermelon stalls when nights stay cool. Watermelon prefers full sun, 36-60 in spacing, and soil near 70 F+.

For fall, count backward from Nov 20. A conservative last sowing target is around Aug 22.