GrowZone

ZIP 21201 planting calendar

When to plant watermelon in Baltimore, MD - Zone 7b

In ZIP 21201, plant watermelon around Apr 29; this uses the Baltimore frost station, USDA zone 7b, and watermelon timing rules.

Your Baltimore calendar has a 204-day estimated frost-free season. This estimate uses the representative Baltimore frost station, USDA zone 7b, and watermelon timing rules.

Source: baltimore-inner-harbor frost station, USDA zone 7b, 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 baltimore-inner-harbor frost station and USDA zone 7b, last updated 2026-06-28.

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

USDA zone 7b Baltimore frost station University of Maryland Extension Updated 2026-06-28
Read the method

Put your planting dates on your calendar

Add to Google Calendar Add to Apple Calendar

Answer first

When to start watermelon seeds indoors in Baltimore

In ZIP 21201, start watermelon seeds indoors around Mar 25, about 21 days before the Apr 15 last-frost estimate.

Start watermelon seeds indoors in Baltimore around Mar 25, about 21 days before the Apr 15 last-frost estimate.

Seed starting schedule

Watermelon dates for Baltimore, MD

StepDateHow to use it
Start IndoorsMarch 25, 2026Start seeds under lights or in a bright indoor seed-starting space.
Transplant OutdoorsApril 29, 2026Move hardened-off seedlings outside after the frost-risk window.
Direct SowApril 29, 2026Sow seed outside when the crop and soil can handle the window.

Last frost

When is the last frost in Baltimore?

Baltimore (ZIP 21201) has an average last spring frost around Apr 15.

First frost

When is the first frost in Baltimore?

The average first fall frost is around Nov 5, giving about 204 frost-free days.

Season map

Watermelon windows by month

JanFebMarAprMayJunJulAugSepOctNovDec
Start indoors
Mar 25
Direct sow
Apr 29
Transplant
Apr 29
Harvest
Jul 28
Frost watch
Aug 7

Reminder workflow

Every date has a next action

Start watermelon indoorsMar 25
Last frost windowApr 15
Direct sow watermelonApr 29
Transplant watermelonApr 29
First watermelon harvest windowJul 28
Last watermelon sowing targetAug 7
SignalValueWhy it matters
Last frost estimateApril 15, 2026Warm-season transplant risk starts falling after this window.
First frost estimateNovember 5, 2026Fall planting counts backward from this date.
Season length204 daysLonger seasons can support succession crops.
Spacing36-60 inAirflow and root space affect yield.
Soil temperature70 F+Seeds and transplants stall in cold soil.

GrowZone may earn from qualifying seed or supply links when real affiliate IDs are configured. No monetized links are active without disclosure.

Local data

Why this date changes by ZIP

Baltimore frost history and USDA zone 7b shift the safe planting window. GrowZone uses a local representative station instead of one national rule.

University of Maryland 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 5. A conservative last sowing target is around Aug 7.