When to plant watermelons in Pierre: 25 May – 15 July

In Pierre, watermelon: sow for seedlings from 6 April to 17 June; plant into a greenhouse from 4 May to 15 July; plant out into open ground from 25 May to 15 July.

Watermelon in Pierre: soil, season and weather

In Pierre the soil, not frost, sets the date: the last frost is over around 26 April, but the top 7 cm of soil reaches 18 °C — the minimum on the watermelon card — only around 25 May, 29 days later.

Last spring frost	26 April
Top 7 cm of soil at 18 °C	25 May, 29 days after the last frost
Into an unheated greenhouse	4 May – 15 July; May outside: 9.9 °C at night, 21.8 °C by day; card 18–35 °C
First autumn frost	24 October, 152 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	23 July – 12 September
Days left for picking	93
Daylight	14:01 on 27 April, 15:06 on 25 May
Watering outdoors when fruiting (card)	every 5 days; the driest month, October, has 6 rainy days

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

Watermelon in Pierre: care after planting

Planted on 25 May: in the first weeks water every 5 days.

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

25 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 Pierre during the watermelon season

No month of the season averages above the watermelon card's 18–35 °C by day; the warmest, July, averages 31.7 °C. Months that stay below 18 °C even by day on average: October (16.5 °C). Nights average below 18 °C in May, June and September, October (5.9–17 °C).

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
May	21.8	9.9	83	11	14:46
June	29.3	17	67	8	15:31
July	31.7	19.7	68	9	15:13
August	30.2	18.4	59	7	14:04
September	26.3	14.5	50	6	12:34
October	16.5	5.9	41	6	11:03

ERA5 2016–2025, Open-Meteo

Watermelon in nearby cities

Around Pierre, Grand Island is 7 days earlier and Rapid City 12 days later.

City	Distance	Date	Difference
Rapid City	233 km	6 June – 3 July	12 days later
Bismarck	274 km	31 May – 6 July	6 days later
Sioux Falls	302 km	24 May – 12 July	1 day earlier
Fargo	391 km	31 May – 7 July	6 days later
Grand Island	416 km	18 May – 18 July	7 days earlier
Grand Forks	467 km	5 June – 7 July	11 days later

Where to buy watermelon plants and seeds near Pierre

Buy plants ready to set out from 25 May to 15 July (from 4 May to 15 July for an unheated greenhouse); seed for raising your own is sown from 6 April to 17 June. Within 15 km of Pierre OpenStreetMap lists 1 market (collected 28 October 2026).

The Alley Exchange — market
South Pierre Street 339, 57501 Pierre · 3 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