When to plant watermelons in Thunder Bay: 8 July – 14 July

In Thunder Bay, watermelon: sow for seedlings from 20 May to 16 June; plant into a greenhouse from 17 June to 14 July; plant out into open ground from 8 July to 14 July.

Watermelon 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 18 °C — the minimum on the watermelon card — only around 8 July, 58 days later. 107 days separate planting out (8 July) from the first autumn frost (23 October); the card's 59 days to the first harvest leave 48 for picking, so a start 6 weeks late would still fit.

Last spring frost	11 May
Top 7 cm of soil at 18 °C	8 July, 58 days after the last frost
Into an unheated greenhouse	17 June – 14 July; June outside: 10.4 °C at night, 19.9 °C by day; card 18–35 °C
First autumn frost	23 October, 107 days after the start
Days in the bed to the first harvest (card)	59
First harvest, if planted in this window	5 September – 11 September
Days left for picking	48
Daylight	16:01 on 10 June, 15:55 on 8 July
Watering outdoors when fruiting (card)	every 5 days; the driest month, August, has 11 rainy days

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

Watermelon in Thunder Bay: care after planting

Planted on 8 July: in the first weeks water every 5 days.

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

8 July — 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 Thunder Bay during the watermelon season

No month of the season averages above the watermelon card's 18–35 °C by day; the warmest, July, averages 23.6 °C. Months that stay below 18 °C even by day on average: October (10.5 °C). Nights average below 18 °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
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

Watermelon in nearby cities

All the nearest cities on our list plant watermelon earlier than Thunder Bay; the closest date is in Duluth, 10 days earlier.

City	Distance	Date	Difference
Duluth	279 km	28 June – 19 July	10 days earlier
Green Bay	439 km	27 May – 21 July	42 days earlier
Minneapolis	487 km	28 May – 15 July	41 days earlier
Traverse City	488 km	5 June – 31 July	33 days earlier
Grand Forks	584 km	5 June – 7 July	33 days earlier
Fargo	589 km	31 May – 7 July	38 days earlier

Where to buy watermelon plants and seeds near Thunder Bay

Buy plants ready to set out from 8 July to 14 July (from 17 June to 14 July for an unheated greenhouse); seed for raising your own is sown from 20 May to 16 June. 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