GrowZone

ZIP 80202 planting calendar

When to plant watermelon in Denver, CO - Zone 6a

In ZIP 80202, plant watermelon around May 19; this uses the Denver frost station, USDA zone 6a, and watermelon timing rules.

Your Denver calendar has a 153-day estimated frost-free season. This estimate uses the representative Denver frost station, USDA zone 6a, and watermelon timing rules.

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

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

USDA zone 6a Denver frost station Colorado State University 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 Denver

In ZIP 80202, start watermelon seeds indoors around Apr 14, about 21 days before the May 5 last-frost estimate.

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

Seed starting schedule

Watermelon dates for Denver, CO

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 Denver?

Denver (ZIP 80202) has an average last spring frost around May 5.

First frost

When is the first frost in Denver?

The average first fall frost is around Oct 5, giving about 153 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 7

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 7
First watermelon harvest windowAug 17
SignalValueWhy it matters
Last frost estimateMay 5, 2026Warm-season transplant risk starts falling after this window.
First frost estimateOctober 5, 2026Fall planting counts backward from this date.
Season length153 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

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

Colorado 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 5. A conservative last sowing target is around Jul 7.