When to plant watermelons in Bismarck: 31 May – 6 July

In Bismarck, watermelon: sow for seedlings from 12 April to 8 June; plant into a greenhouse from 10 May to 6 July; plant out into open ground from 31 May to 6 July.

Watermelon in Bismarck: soil, season and weather

In Bismarck the soil, not frost, sets the date: the last frost is over around 1 May, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 31 May, 30 days later.

Last spring frost	1 May
Top 7 cm of soil at 18 °C	31 May, 30 days after the last frost
Into an unheated greenhouse	10 May – 6 July; May outside: 7.4 °C at night, 20.2 °C by day; card 18–35 °C
First autumn frost	15 October, 137 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	29 July – 3 September
Days left for picking	78
Daylight	14:29 on 3 May, 15:34 on 31 May
Watering outdoors when fruiting (card)	every 5 days; the driest month, October, has 5 rainy days

The same dates in Bismarck hold for Cucumber, Bell Pepper, Eggplant, Zucchini and Pumpkin.

Watermelon in Bismarck: care after planting

Planted on 31 May: in the first weeks water every 5 days.

Feeding, by the card’s schedule from that day:

31 May — feed: balanced (NPK)

Pests and diseases of watermelon to watch for:

Dates count from the first planting day of the window above; a later planting moves them by as many days.

Weather in Bismarck during the watermelon season

No month of the season averages above the watermelon card's 18–35 °C by day; the warmest, July, averages 29.1 °C. Months that stay below 18 °C even by day on average: October (13.7 °C). Nights average below 18 °C in every month of the season, from 3.6 °C to 17.2 °C.

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
May	20.2	7.4	67	10	15:01
June	26.6	14.1	69	9	15:51
July	29.1	17.2	63	8	15:31
August	27.6	15.8	68	8	14:15
September	23.4	11.8	55	7	12:37
October	13.7	3.6	44	5	10:58

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

Around Bismarck, Sioux Falls is 7 days earlier and Rapid City 6 days later.

City	Distance	Date	Difference
Pierre	274 km	25 May – 15 July	6 days earlier
Fargo	303 km	31 May – 7 July	same day
Grand Forks	303 km	5 June – 7 July	5 days later
Rapid City	360 km	6 June – 3 July	6 days later
Winnipeg	436 km	1 June – 3 July	1 day later
Sioux Falls	482 km	24 May – 12 July	7 days earlier

Where to buy watermelon plants and seeds near Bismarck

Buy plants ready to set out from 31 May to 6 July (from 10 May to 6 July for an unheated greenhouse); seed for raising your own is sown from 12 April to 8 June. Within 15 km of Bismarck OpenStreetMap lists 1 garden centre and 1 market (collected 28 October 2026).

Bismarket — market
South Washington Street 318, 58504 Bismarck · Jun–Oct Sat 10:00–13:00 · 2 km · bismarket.com
Lowe's Plant Section — garden centre
4 km

Each window starts on the Greenly calendar date and ends on the last day that still leaves the crop’s days to harvest (from its card) before the average first autumn frost, plus six weeks of picking for crops harvested over weeks (tomatoes, peppers, aubergines, cucumbers, courgettes, pumpkins, watermelons, beans) — our rule; earlier in the window is safer.

Questions