When to plant tomatoes in Thunder Bay: 22 June – 3 July

In Thunder Bay, tomato: sow for seedlings from 10 April to 12 May; plant into a greenhouse from 1 June to 3 July; plant out into open ground from 22 June to 3 July.

Tomato in Thunder Bay: soil, season and weather

In Thunder Bay the soil, not frost, sets the date: the last frost is over around 11 May, but the top 7 cm of soil reaches 15 °C — the minimum on the tomato card — only around 22 June, 42 days later. 123 days separate planting out (22 June) from the first autumn frost (23 October); the card's 70 days to the first harvest leave 53 for picking, so a start 7 weeks late would still fit.

Last spring frost	11 May
Top 7 cm of soil at 15 °C	22 June, 42 days after the last frost
Into an unheated greenhouse	1 June – 3 July; June outside: 10.4 °C at night, 19.9 °C by day; card 16–27 °C
First autumn frost	23 October, 123 days after the start
Days in the bed to the first harvest (card)	70
First harvest, if planted in this window	31 August – 11 September
Days left for picking	53
Daylight	14:31 on 1 May, 16:06 on 22 June
Watering outdoors when fruiting (card)	every 3 days; the driest month, August, has 11 rainy days

Tomato in Thunder Bay: care after planting

Planted on 22 June: in the first weeks water every 4 days.

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

22 June — feed: balanced (NPK)
20 July — 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 Thunder Bay during the tomato season

No month of the season averages above the tomato card's 16–27 °C by day; the warmest, July, averages 23.6 °C. Months that stay below 16 °C even by day on average: October (10.5 °C). Nights average below 16 °C in every month of the season, from 4.2 °C to 14.4 °C.

Month	Day, °C	Night, °C	Rain, mm	Rainy days	Daylight on the 15th
June	19.9	10.4	81	10	16:05
July	23.6	14.4	74	11	15:44
August	22.3	14.2	63	11	14:23
September	18.2	10.9	86	11	12:38
October	10.5	4.2	71	10	10:54

ERA5 2016–2025, Open-Meteo

Tomato in nearby cities

All the nearest cities on our list plant tomato earlier than Thunder Bay; the closest date is in Duluth, 17 days earlier.

City	Distance	Date	Difference
Duluth	279 km	5 June – 8 July	17 days earlier
Green Bay	439 km	19 May – 10 July	34 days earlier
Minneapolis	487 km	18 May – 4 July	35 days earlier
Traverse City	488 km	27 May – 20 July	26 days earlier
Grand Forks	584 km	24 May – 26 June	29 days earlier
Fargo	589 km	18 May – 26 June	35 days earlier

Where to buy tomato plants and seeds near Thunder Bay

Buy plants ready to set out from 22 June to 3 July (from 1 June to 3 July for an unheated greenhouse); seed for raising your own is sown from 10 April to 12 May. Within 15 km of Thunder Bay OpenStreetMap lists 2 garden centres and 1 market (collected 20 October 2026).

Goods & Co. — market
Red River Road 251 · 7 km · goodscomarket.ca
Trevisanutto's Garden Centre — garden centre
7 km
Creekside Nursery — garden centre
7 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