When to plant watermelons in Grand Forks: 5 June – 7 July

In Grand Forks, watermelon: sow for seedlings from 17 April to 9 June; plant into a greenhouse from 15 May to 7 July; plant out into open ground from 5 June to 7 July.

Watermelon in Grand Forks: soil, season and weather

In Grand Forks the soil, not frost, sets the date: the last frost is over around 10 May, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 5 June, 26 days later.

Last spring frost	10 May
Top 7 cm of soil at 18 °C	5 June, 26 days after the last frost
Into an unheated greenhouse	15 May – 7 July; May outside: 7.9 °C at night, 20.5 °C by day; card 18–35 °C
First autumn frost	16 October, 133 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	3 August – 4 September
Days left for picking	74
Daylight	14:49 on 8 May, 15:51 on 5 June
Watering outdoors when fruiting (card)	every 5 days; the driest month, September, has 8 rainy days

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

Watermelon in Grand Forks: care after planting

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

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

5 June — 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 Grand Forks during the watermelon season

No month of the season averages above the watermelon card's 18–35 °C by day; the warmest, July, averages 27.9 °C. Months that stay below 18 °C even by day on average: October (12.8 °C). Nights average below 18 °C in every month of the season, from 4.2 °C to 17.1 °C.

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
June	26.3	14.8	89	10	16:00
July	27.9	17.1	72	8	15:40
August	26.3	15.9	61	9	14:20
September	22.2	12.3	60	8	12:38
October	12.8	4.2	60	8	10:55

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

Around Grand Forks, Pierre is 11 days earlier and Duluth 23 days later.

City	Distance	Date	Difference
Fargo	118 km	31 May – 7 July	5 days earlier
Winnipeg	220 km	1 June – 3 July	4 days earlier
Bismarck	303 km	31 May – 6 July	5 days earlier
Duluth	396 km	28 June – 19 July	23 days later
Minneapolis	439 km	28 May – 15 July	8 days earlier
Pierre	467 km	25 May – 15 July	11 days earlier

Where to buy watermelon plants and seeds near Grand Forks

Buy plants ready to set out from 5 June to 7 July (from 15 May to 7 July for an unheated greenhouse); seed for raising your own is sown from 17 April to 9 June. Within 15 km of Grand Forks OpenStreetMap lists 2 markets (collected 29 October 2026).

Town Square Farmers Market — market
Jun 17–Sept 30 Sat 09:00–13:00 · 5 km · tsfarmersmarket.com
Daryeel Grocerys — market
5 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