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ZIP 48226 planting calendar

When to plant watermelon in Detroit, MI - Zone 6b

In ZIP 48226, plant watermelon around May 19; this uses the Detroit frost station, USDA zone 6b, and watermelon timing rules.

Your Detroit calendar has a 163-day estimated frost-free season. This estimate uses the representative Detroit frost station, USDA zone 6b, and watermelon timing rules.

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

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

USDA zone 6b Detroit frost station Michigan State University Extension Updated 2026-06-28
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Answer first

When to start watermelon seeds indoors in Detroit

In ZIP 48226, start watermelon seeds indoors around Apr 14, about 21 days before the May 5 last-frost estimate.

Start watermelon seeds indoors in Detroit around Apr 14, about 21 days before the May 5 last-frost estimate.

Seed starting schedule

Watermelon dates for Detroit, MI

StepDateHow to use it
Start IndoorsApril 14, 2026Start seeds under lights or in a bright indoor seed-starting space.
Transplant OutdoorsMay 19, 2026Move hardened-off seedlings outside after the frost-risk window.
Direct SowMay 19, 2026Sow seed outside when the crop and soil can handle the window.

Last frost

When is the last frost in Detroit?

Detroit (ZIP 48226) has an average last spring frost around May 5.

First frost

When is the first frost in Detroit?

The average first fall frost is around Oct 15, giving about 163 frost-free days.

Season map

Watermelon windows by month

JanFebMarAprMayJunJulAugSepOctNovDec
Start indoors
Apr 14
Direct sow
May 19
Transplant
May 19
Harvest
Aug 17
Frost watch
Jul 17

Reminder workflow

Every date has a next action

Start watermelon indoorsApr 14
Last frost windowMay 5
Direct sow watermelonMay 19
Transplant watermelonMay 19
Last watermelon sowing targetJul 17
First watermelon harvest windowAug 17
SignalValueWhy it matters
Last frost estimateMay 5, 2026Warm-season transplant risk starts falling after this window.
First frost estimateOctober 15, 2026Fall planting counts backward from this date.
Season length163 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

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

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