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ZIP 78205 planting calendar

When to plant watermelon in San Antonio, TX - Zone 9a

In ZIP 78205, plant watermelon around Mar 15; this uses the San Antonio frost station, USDA zone 9a, and watermelon timing rules.

Your San Antonio calendar has a 264-day estimated frost-free season. This estimate uses the representative San Antonio frost station, USDA zone 9a, and watermelon timing rules.

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

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

USDA zone 9a San Antonio frost station Texas A&M AgriLife Extension Updated 2026-06-28
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Answer first

When to start watermelon seeds indoors in San Antonio

In ZIP 78205, start watermelon seeds indoors around Feb 8, about 21 days before the Mar 1 last-frost estimate.

Start watermelon seeds indoors in San Antonio around Feb 8, about 21 days before the Mar 1 last-frost estimate.

Seed starting schedule

Watermelon dates for San Antonio, TX

StepDateHow to use it
Start IndoorsFebruary 8, 2026Start seeds under lights or in a bright indoor seed-starting space.
Transplant OutdoorsMarch 15, 2026Move hardened-off seedlings outside after the frost-risk window.
Direct SowMarch 15, 2026Sow seed outside when the crop and soil can handle the window.

Last frost

When is the last frost in San Antonio?

San Antonio (ZIP 78205) has an average last spring frost around Mar 1.

First frost

When is the first frost in San Antonio?

The average first fall frost is around Nov 20, giving about 264 frost-free days.

Season map

Watermelon windows by month

JanFebMarAprMayJunJulAugSepOctNovDec
Start indoors
Feb 8
Direct sow
Mar 15
Transplant
Mar 15
Harvest
Jun 13
Frost watch
Aug 22

Reminder workflow

Every date has a next action

Start watermelon indoorsFeb 8
Last frost windowMar 1
Direct sow watermelonMar 15
Transplant watermelonMar 15
First watermelon harvest windowJun 13
Last watermelon sowing targetAug 22
SignalValueWhy it matters
Last frost estimateMarch 1, 2026Warm-season transplant risk starts falling after this window.
First frost estimateNovember 20, 2026Fall planting counts backward from this date.
Season length264 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

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

Texas A&M AgriLife 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.