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ZIP 85001 planting calendar

When to plant watermelon in Phoenix, AZ - Zone 10a

In ZIP 85001, plant watermelon around Feb 19; this uses the Phoenix frost station, USDA zone 10a, and watermelon timing rules.

Your Phoenix calendar has a 313-day estimated frost-free season. This estimate uses the representative Phoenix frost station, USDA zone 10a, and watermelon timing rules.

Source: phoenix-skyharbor frost station, USDA zone 10a, 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 phoenix-skyharbor frost station and USDA zone 10a, last updated 2026-06-28.

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

USDA zone 10a Phoenix frost station University of Arizona Extension Updated 2026-06-28
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Answer first

When to start watermelon seeds indoors in Phoenix

In ZIP 85001, start watermelon seeds indoors around Jan 15, about 21 days before the Feb 5 last-frost estimate.

Start watermelon seeds indoors in Phoenix around Jan 15, about 21 days before the Feb 5 last-frost estimate.

Seed starting schedule

Watermelon dates for Phoenix, AZ

StepDateHow to use it
Start IndoorsJanuary 15, 2026Start seeds under lights or in a bright indoor seed-starting space.
Transplant OutdoorsFebruary 19, 2026Move hardened-off seedlings outside after the frost-risk window.
Direct SowFebruary 19, 2026Sow seed outside when the crop and soil can handle the window.

Last frost

When is the last frost in Phoenix?

Phoenix (ZIP 85001) has an average last spring frost around Feb 5.

First frost

When is the first frost in Phoenix?

The average first fall frost is around Dec 15, giving about 313 frost-free days.

Season map

Watermelon windows by month

JanFebMarAprMayJunJulAugSepOctNovDec
Start indoors
Jan 15
Direct sow
Feb 19
Transplant
Feb 19
Harvest
May 20
Frost watch
Sep 16

Reminder workflow

Every date has a next action

Start watermelon indoorsJan 15
Last frost windowFeb 5
Direct sow watermelonFeb 19
Transplant watermelonFeb 19
First watermelon harvest windowMay 20
Last watermelon sowing targetSep 16
SignalValueWhy it matters
Last frost estimateFebruary 5, 2026Warm-season transplant risk starts falling after this window.
First frost estimateDecember 15, 2026Fall planting counts backward from this date.
Season length313 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

Phoenix frost history and USDA zone 10a shift the safe planting window. GrowZone uses a local representative station instead of one national rule.

University of Arizona 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 Dec 15. A conservative last sowing target is around Sep 16.