When to Plant Watermelon: Soil Temperature, Frost Dates and Regional Windows

Watermelon goes into the garden after frost danger has passed and the soil 4 inches (10 cm) below the surface holds 65°F (18°C) or more. On the calendar, that is 1 to 2 weeks after the date when only 1 spring in 10 still brings a later frost. Across most of the country it falls between early April and early June, and sowing should be finished by mid- to late June.

Two choices shift the date within that window. Transplants can go out once the soil reaches 60°F (16°C) and ripen up to 2 weeks sooner; seed sown straight into the garden wants 70°F (21°C). Black plastic and row covers can buy a little more time where summers are short.

Watermelon planting dates by city

Start in the first date column once the soil passes 65°F, and sow seed no later than the second.

Frost dates are medians from NOAA 1991–2020 climate normals for each city's main weather station; in half of years the last frost falls later than the date shown.

The start column opens 7 to 14 days after each city's 1-in-10 last-frost date, the date after which frost strikes in only 1 year in 10. In Zones 6 and colder, the last-sowing column counts back 121 to 128 days from the median first frost, the latest that seed of an early variety still ripens. Most Zone 7 and 8 cities close in mid- to late June, Dallas-Fort Worth ends its spring planting in mid-April, and the coastal Northeast and the three Zone 9 cities follow the soil and local calendars.

For any other town, add 3 to 4 weeks to your median last spring frost, or 1 to 2 weeks to the 1-in-10 date, and plant on the first day the soil test below passes. North of Zone 7, find the last sowing date by counting back about 18 weeks from your median first fall frost. In Zones 7 and 8, finish by mid- to late June, or earlier in Texas and along the Gulf.

The start dates sit about 3 to 4 weeks after each median frost on purpose. Watermelon has no frost tolerance at all, and even a light frost badly injures the vines, so the rule waits for the date when a late frost has become unlikely rather than merely possible.

A few rows deserve a second look. Boston's frost dates come from Logan Airport on the harbor and New York's from Central Park, and both medians fall early in spring. Plant there once the soil holds 65°F (18°C); in nearby New England that usually comes at the end of May or the first days of June. Fargo and Denver are the opposite case: their seasons are too short for much margin, so set out transplants of a fast variety. A Sugar Baby transplant planted in Fargo on June 6 needs about 75 days, ripening around August 20, roughly 6 weeks before the median first frost.

Seattle, Sacramento and Houston have early last frosts, but frost is not what holds them back. West of the Cascades, transplants go out in early June. Sacramento sows seed from mid-April through June, and Houston plants in April and May.

Planting windows by region

North of Zone 7 the window falls in May or June; across the South it falls in April, and in Florida and the low desert it moves into late winter.

Windows are for the main spring planting; the soil test still overrides the date in a cold spring.

Upper Midwest and northern plains. Short summers make watermelon transplants and early varieties the safe plan here, set into soil warmed under black plastic. Iowa's mid-May planting moves later as you go north; in Minnesota and the Dakotas, use the city table.

Mountain West. Denver's window opens around May 26 and Salt Lake City's around May 7. Transplants mature about 2 weeks earlier than seeded melons, which makes them the recommended route in short-season Utah gardens. In Colorado, sow seed directly once the soil is warm, or use a transplant only 2 to 3 weeks old so the roots are disturbed as little as possible.

Texas and the Gulf Coast. Plant 1 to 6 weeks after the average last frost, once frost danger is over and the seed zone tops 70°F (21°C), with transplants preferred. Around Dallas-Fort Worth that runs from mid-March to mid-April, and the city table's dates sit in the later half because they wait for warm soil. Around Houston, April and May are the ideal months.

Low desert. Sow seed from mid-February to mid-March and not before the soil warms. Low-desert melons take 90 to 120 days, and growth slows once days pass 95°F (35°C).

Pacific Northwest. Plant in May in the western Oregon valleys and in early June west of the Cascades in Washington, always from transplants. Watermelon is not recommended on the Oregon coast or at high elevation.

California. In the Sacramento Valley, sow seed in the garden from mid-April through June, once a morning reading at 4 inches (10 cm) holds 70°F (21°C), the temperature seed needs.

How to tell the soil is ready

Push a soil thermometer 4 inches (10 cm) into the bed at about 8 a.m., when the soil is coolest, and plant once it reads 65°F (18°C).

Recommended thresholds span 10 degrees, and the method of planting explains most of the spread. Transplants can go out into 60°F (16°C) soil. Seed needs 70°F (21°C) and germinates fastest near 90°F (32°C). A 65°F (18°C) reading covers both reasonably well. A kitchen meat thermometer works if you have no soil probe.

Check the air as well. Watermelon grows best when days run 80–95°F (27–35°C) and nights stay at 60–70°F (16–21°C), and growth stalls below 50°F (10°C). Wait until days stay consistently above 55°F (13°C).

Gaining time with black plastic and row covers

Black plastic mulch warms a cold bed and brings the crop on earlier. Lay it over moist soil and cut a hole for each plant; it works well stretched over a mounded or raised bed. Under black plastic with a floating row cover kept on, you can plant up to 2 to 3 weeks before the last frost, but only once the soil under the plastic reads 65°F (18°C). Leave the cover in place through every cold night.

The row cover must come off when the first female flowers open, so bees can reach them. Hold off on straw or other organic mulch until the soil passes 75°F (24°C).

Transplants or direct seed

Grow transplants wherever the season is short, and sow directly only where warm soil arrives early and summers are long.

Start watermelon indoors 3 to 4 weeks before your outdoor planting date, not before your last frost. Some seed packets count back from the last frost, which leaves seedlings ready a week or two before the soil is. Seedlings that grow too big for their pots become root-bound and transplant poorly, so a late start is safer than an early one. In the coldest regions a 4- to 6-week-old transplant is acceptable, but treat that as the outer limit.

Watermelon roots resent disturbance. Sow 2 to 3 seeds in a peat or other plantable pot and keep the strongest. Set seedlings out when they carry 1 to 3 true leaves, after 4 to 7 days of hardening off outdoors in a sheltered spot. Plant the whole pot, or slide the root ball out without breaking it.

Direct sowing costs time. Catalog days often count from transplanting, so add 10 to 14 days when you sow seed in the garden. Where soil reaches 70°F (21°C) in spring and the frost-free season runs long, as in the low desert, direct sowing is the norm.

Planting depth and spacing

Sow watermelon seed about 1 inch (2.5 cm) deep, 2 to 5 seeds to a hill, and thin each hill to the strongest 1 to 3 plants.

Recommended depths range from 1/2 inch (1.3 cm) on seed packets to 1.5–2 inches (4–5 cm) in Florida plantings. Spacing depends on how much ground you can give the vines.

Allow 18–24 square feet (1.7–2.2 m²) per plant; compact Sugar Baby can go 12–18 inches (30–45 cm) apart in 6-foot (1.8 m) rows.

Varieties that change the timing

The variety moves your harvest by a month: a fast icebox watermelon ripens in under 70 days, while a large heirloom needs 90 to 100.

Days are average days to maturity from variety trials and seed catalogs; Sugar Baby's count from transplanting, so add 10–14 days for seed sown in the garden.

In the North, pick from the fast end. Yellow Doll, Lantha and Sugar Baby suit Fargo, Minneapolis and Denver, where planting closes around mid-June or earlier and the median first frost falls between late September and mid-October. Save Moon and Stars for a long season, such as an April planting in the South.

Seedless melons set no fruit on their own, so plant a seeded variety alongside as a pollenizer. Seedless fruit is often sweeter, which repays the extra planning.

Planting too early or too late

Early planting gambles the crop on frost and cold soil; late planting leaves fruit ripening as autumn nights cool.

Watermelon seed in cold soil rots, and the seedlings that do emerge are prone to disease. A transplant set out too soon stops growing while the soil and nights stay cold, and a single frost can ruin it.

Late planting costs flavor as well as fruit. Melons that ripen during a short or cool season taste flat. In central Iowa, June 20 is the last practical sowing date, and only for early varieties. In the South Carolina Piedmont the window closes June 15. To test a late date, count your variety's days to maturity forward from planting. If the fruit would still be ripening when your median first fall frost arrives, choose a faster variety.

A fall crop works only where the season is very long: Texas plants one 14 to 16 weeks before the first freeze, while South Carolina does not recommend it. Once the vines come out, use the bed for a cool-season crop such as garlic.

If a late frost threatens

Cover plants before sunset with a floating row cover, which gives some frost protection; it can stay in place until the first female flowers open. If frost kills a planting, replace it with transplants rather than seed; that recovers the most time. In northern gardens, resow only a variety short enough to ripen before your first fall frost.

From planting to harvest

Each watermelon fruit ripens about 35 to 45 days after its flower is pollinated, and a healthy vine carries 2 to 3 melons.

In dry weather, give 1 to 2 inches (2.5–5 cm) of water every 7 to 10 days. As the fruit nears full size, halve the amount applied each time, but do not let the vines wilt.

Judge ripeness by the ground spot, the tendril nearest the fruit and the rind together. In some varieties the tendril browns 7 to 10 days before the fruit is ready, so it is never enough on its own.

Store picked melons at 50–60°F (10–16°C); below 40°F (4°C) the fruit suffers chilling injury. A 25- to 40-pound (11–18 kg) heirloom is a two-handed lift, so bend your knees and carry it close.

The same frost-and-soil logic sets the date for other warm-season crops; see tomato planting times and pumpkin planting dates. To keep your watermelon window alongside the rest of your vegetable planting dates, add it to Sow's garden calendar.