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When to Plant Watermelon

Dates to sow watermelon outdoors for your ZIP code or zone.

Tomato and pepper seedlings in trays under an LED grow light

Watermelon planting dates by zone

At the average last frost date for each USDA half-zone (the median across its ZIP codes, NOAA 1991 to 2020 normals). Enter your ZIP code below for your own dates.

ZoneLast frostSow outdoors
3aMay 28Jun 4 to Jun 11
3bMay 17May 24 to May 31
4aMay 13May 20 to May 27
4bMay 8May 15 to May 22
5aMay 4May 11 to May 18
5bMay 1May 8 to May 15
6aApr 29May 6 to May 13
6bApr 23Apr 30 to May 7
7aApr 16Apr 23 to Apr 30
7bApr 6Apr 13 to Apr 20
8aMar 29Apr 5 to Apr 12
8bMar 18Mar 25 to Apr 1
9aMar 3Mar 10 to Mar 17
9bFeb 2Feb 9 to Feb 16
10aJan 16Jan 23 to Jan 30
10brareby season
Your location

Zone medians. Your ZIP code gives the dates of your nearest weather station.

Frost risk

Half of years still get a frost after the spring date, and half get the first fall frost before the fall date.

Frost dates at three risk levels
AverageSaferSafest
Last spring frostApr 23Apr 30May 9
First fall frostOct 22Oct 16Oct 7
Crops (1 selected)

First job: sow seeds outdoors

Apr 30watermelon

Average frost dates: last Apr 23, first Oct 22 (zone 6b).
Season
Spring seed starting schedule
CropSow outdoorsNotes
WatermelonVery tenderApr 30 to May 7Sow outdoors 1 to 2 wk after last frost. Sprouts in 3 to 12 days, best at 70 to 95°F soil.

How to start seeds indoors

Light
Give seedlings 14 to 18 hours of light a day on a timer, with fluorescent or LED fixtures 2 to 6 in above the leaves. Raise the lights as the plants grow.
Clemson HGIC: 16 to 18 hours, tubes 2 to 4 in above. UMD Extension: 14 to 16 hours, 2 to 6 in.
Seed starting mix
Use a sterile, soilless mix, never garden soil. To mix your own, combine equal parts by volume of fine pine bark, sphagnum peat moss and perlite.
NC State Extension Gardener Handbook; Clemson HGIC.
Sowing and warmth
Sow two or three seeds per cell and keep the strongest seedling. A mix temperature of 65 to 75°F germinates most vegetables; after they sprout, 55 to 60°F nights and 65 to 70°F days keep them stocky.
UMD Extension.
Potting up
Move seedlings into larger pots shortly after the first true leaves appear, while they are small and recover quickly.
UMD Extension; Clemson HGIC (one or two sets of true leaves).
Hardening off
Start two to three weeks before transplanting, once plants are about 3 in tall: set them outdoors by day, bring them in before sundown, and give them more direct sun each day. Skip days below 45°F or with strong wind.
Clemson HGIC: 2 to 3 weeks. NC State: at least 2 weeks, not below 45°F.

When to plant watermelon

Watermelon goes in after the frost, not before it. Colorado State University Extension sows the seed outdoors 1 to 2 weeks after the average last spring frost, and Utah State University Extension waits until the soil has reached 65°F. The table above gives the sowing window for every USDA zone, and the planner below it works out your own dates from your ZIP code.

Sow outdoors = last frost date + 1 week to last frost date + 2 weeks

Example dates by zone

At the median last frost for each half-zone (NOAA 1991 to 2020 normals):

ZoneAverage last frostSow outdoorsDays to first frost from the first sowing
4bMay 8May 15 to May 22139
5bMay 1May 8 to May 15155
7aApr 16Apr 23 to Apr 30185
9aMar 3Mar 10 to Mar 17260

Colorado State gives about 85 days from seed to harvest. Even zone 4b, with the average first fall frost on Oct 1, leaves 139 days after a May 15 sowing, so the season is long enough at average dates. The planner warns you when your own dates get tight.

Why the wait matters

Watermelon is rated very tender: frost kills it. Cold soil is the other problem. Oregon State University Extension's germination table puts the minimum soil temperature at 60°F and the best range at 70 to 95°F. Colorado State's 1 to 2 week delay after the frost date gives the soil that time to warm. A soil thermometer at planting depth, 1 to 1½ inches, settles the question better than the calendar.

Starting watermelon indoors

The planner shows outdoor sowing only, because that is how the sources above plant it. Utah State does recommend transplants where the season is short: allow about 6 weeks to grow them, plant when they have 2 to 3 mature leaves, and expect them to ripen about 2 weeks before seeded melons. Count the 6 weeks back from your outdoor date: in zone 5b, a May 8 planting means sowing indoors around Mar 27.

Next questions

  • How far apart? 3 to 4 ft in the row, rows 5 to 10 ft apart; the watermelon spacing calculator counts plants for your bed or row.
  • How many seeds? Utah State sows 4 to 6 seeds per mound and thins to 2 plants.
  • Other warm crops on the same calendar? The seed starting calculator puts watermelon next to squash, cucumbers and tomatoes; see the squash planting dates for a crop that goes in a week earlier.