When to plant tomatoes in Grand Forks: 24 May – 26 June

In Grand Forks, tomato: sow for seedlings from 12 March to 5 May; plant into a greenhouse from 3 May to 26 June; plant out into open ground from 24 May to 26 June.

Tomato 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 15 °C — the minimum on the tomato card — only around 24 May, 14 days later.

Last spring frost	10 May
Top 7 cm of soil at 15 °C	24 May, 14 days after the last frost
Into an unheated greenhouse	3 May – 26 June; May outside: 7.9 °C at night, 20.5 °C by day; card 16–27 °C
First autumn frost	16 October, 145 days after the start
Days in the bed to the first harvest (card)	70
First harvest, if planted in this window	2 August – 4 September
Days left for picking	75
Daylight	12:53 on 2 April, 15:30 on 24 May
Watering outdoors when fruiting (card)	every 3 days; the driest month, September, has 8 rainy days

Tomato in Grand Forks: care after planting

Planted on 24 May: in the first weeks water every 4 days.

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

24 May — feed: balanced (NPK)
21 June — feed: nitrogen

Pests and diseases of tomato 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 tomato season

Days average above the tomato card's 16–27 °C in July (27.9 °C). Months that stay below 16 °C even by day on average: October (12.8 °C). Nights average below 16 °C in May, June and August–October (4.2–15.9 °C).

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
May	20.5	7.9	69	10	15:09
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

Tomato in nearby cities

Around Grand Forks, Pierre is 15 days earlier and Duluth 12 days later.

City	Distance	Date	Difference
Fargo	118 km	18 May – 26 June	6 days earlier
Winnipeg	220 km	24 May – 22 June	same day
Bismarck	303 km	22 May – 25 June	2 days earlier
Duluth	396 km	5 June – 8 July	12 days later
Minneapolis	439 km	18 May – 4 July	6 days earlier
Pierre	467 km	9 May – 4 July	15 days earlier

Where to buy tomato plants and seeds near Grand Forks

Buy plants ready to set out from 24 May to 26 June (from 3 May to 26 June for an unheated greenhouse); seed for raising your own is sown from 12 March to 5 May. 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