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ZIP 46204 planting calendar

When to plant watermelon in Indianapolis, IN - Zone 6b

In ZIP 46204, plant watermelon around May 9; this uses the Indianapolis frost station, USDA zone 6b, and watermelon timing rules.

Your Indianapolis calendar has a 173-day estimated frost-free season. This estimate uses the representative Indianapolis frost station, USDA zone 6b, and watermelon timing rules.

Source: indianapolis-intl frost station, USDA zone 6b, 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 indianapolis-intl frost station and USDA zone 6b, last updated 2026-06-28.

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

USDA zone 6b Indianapolis frost station Purdue Extension Updated 2026-06-28
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Answer first

When to start watermelon seeds indoors in Indianapolis

In ZIP 46204, start watermelon seeds indoors around Apr 4, about 21 days before the Apr 25 last-frost estimate.

Start watermelon seeds indoors in Indianapolis around Apr 4, about 21 days before the Apr 25 last-frost estimate.

Seed starting schedule

Watermelon dates for Indianapolis, IN

StepDateHow to use it
Start IndoorsApril 4, 2026Start seeds under lights or in a bright indoor seed-starting space.
Transplant OutdoorsMay 9, 2026Move hardened-off seedlings outside after the frost-risk window.
Direct SowMay 9, 2026Sow seed outside when the crop and soil can handle the window.

Last frost

When is the last frost in Indianapolis?

Indianapolis (ZIP 46204) has an average last spring frost around Apr 25.

First frost

When is the first frost in Indianapolis?

The average first fall frost is around Oct 15, giving about 173 frost-free days.

Season map

Watermelon windows by month

JanFebMarAprMayJunJulAugSepOctNovDec
Start indoors
Apr 4
Direct sow
May 9
Transplant
May 9
Harvest
Aug 7
Frost watch
Jul 17

Reminder workflow

Every date has a next action

Start watermelon indoorsApr 4
Last frost windowApr 25
Direct sow watermelonMay 9
Transplant watermelonMay 9
Last watermelon sowing targetJul 17
First watermelon harvest windowAug 7
SignalValueWhy it matters
Last frost estimateApril 25, 2026Warm-season transplant risk starts falling after this window.
First frost estimateOctober 15, 2026Fall planting counts backward from this date.
Season length173 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

Indianapolis frost history and USDA zone 6b shift the safe planting window. GrowZone uses a local representative station instead of one national rule.

Purdue 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 Oct 15. A conservative last sowing target is around Jul 17.