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ZIP 97204 planting calendar

When to plant watermelon in Portland, OR - Zone 9a

In ZIP 97204, plant watermelon around Apr 15; this uses the Portland frost station, USDA zone 9a, and watermelon timing rules.

Your Portland calendar has a 223-day estimated frost-free season. This estimate uses the representative Portland frost station, USDA zone 9a, and watermelon timing rules.

Source: portland-intl 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 portland-intl frost station and USDA zone 9a, last updated 2026-06-28.

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

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

When to start watermelon seeds indoors in Portland

In ZIP 97204, start watermelon seeds indoors around Mar 11, about 21 days before the Apr 1 last-frost estimate.

Start watermelon seeds indoors in Portland around Mar 11, about 21 days before the Apr 1 last-frost estimate.

Seed starting schedule

Watermelon dates for Portland, OR

StepDateHow to use it
Start IndoorsMarch 11, 2026Start seeds under lights or in a bright indoor seed-starting space.
Transplant OutdoorsApril 15, 2026Move hardened-off seedlings outside after the frost-risk window.
Direct SowApril 15, 2026Sow seed outside when the crop and soil can handle the window.

Last frost

When is the last frost in Portland?

Portland (ZIP 97204) has an average last spring frost around Apr 1.

First frost

When is the first frost in Portland?

The average first fall frost is around Nov 10, giving about 223 frost-free days.

Season map

Watermelon windows by month

JanFebMarAprMayJunJulAugSepOctNovDec
Start indoors
Mar 11
Direct sow
Apr 15
Transplant
Apr 15
Harvest
Jul 14
Frost watch
Aug 12

Reminder workflow

Every date has a next action

Start watermelon indoorsMar 11
Last frost windowApr 1
Direct sow watermelonApr 15
Transplant watermelonApr 15
First watermelon harvest windowJul 14
Last watermelon sowing targetAug 12
SignalValueWhy it matters
Last frost estimateApril 1, 2026Warm-season transplant risk starts falling after this window.
First frost estimateNovember 10, 2026Fall planting counts backward from this date.
Season length223 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

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

Oregon 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 10. A conservative last sowing target is around Aug 12.