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When to plant crocuses in Thunder Bay: 23 September – 30 October

In Thunder Bay, crocus: plant from 23 September to about 30 October.

Bulbs are best planted early in the window: late-planted bulbs may flower later or less well. Late planting works only while the soil can be dug. Mulch after planting.

The date is about two weeks before the average daily temperature here falls below 0 °C (ten years of weather): an estimate, not the day the ground freezes, and a cold spell can freeze it earlier. Sources: Iowa State University Extension, Wisconsin Horticulture Extension, UNH Extension, RHS, how the ground freezes (NRC Canada, CBD-26).

Crocus in Thunder Bay: soil, season and weather

Nights then average below 0 °C in November–April; the coldest, February, averages -15.4 °C.

Planting23 September – 30 October
First autumn frost23 October
Coldest nightsFebruary, -15.4 °C
Soil back at 1 °C in spring21 April
Daylight12:11 on 23 September
Daylight at the winter solstice8:19

The same dates in Thunder Bay hold for Garlic, Tulip, Daffodil and Hyacinth.

Crocus in Thunder Bay: depth, winter cold, pests and pets

Plant Dutch crocuses (Crocus vernus) about 12 cm deep and 9 cm apart; smaller species go 7–10 cm deep (RHS).

In Thunder Bay the average daily temperature stays at 10 °C or lower for about 32 weeks a year (our estimate from ten years of monthly weather). For this bulb Wisconsin Horticulture Extension gives a cold period of 15–17 weeks at about 2–10 °C. The winter here gives that in the ground, so the bulbs need no pre-chilling.

Crocuses multiply on their own (they naturalise); in a lawn, hold off mowing until their leaves die back (RHS).

Birds, squirrels and rodents damage crocuses; planting under metal mesh may reduce losses (RHS). Spring crocus gives dogs and cats vomiting and diarrhoea; do not confuse it with autumn crocus (Colchicum), which is very toxic (Pet Poison Helpline).

Sources: RHS, Wisconsin Horticulture Extension, Pet Poison Helpline.

Crocus in nearby cities

Around Thunder Bay, Fargo is 7 days earlier and Traverse City 17 days later.

CityDistanceDateDifference
Duluth279 km28 September – 10 November5 days later
Green Bay439 km30 September – 17 November7 days later
Minneapolis487 km24 September – 10 November1 day later
Traverse City488 km10 October – 26 November17 days later
Fargo589 km16 September – 4 November7 days earlier
Madison591 km27 September – 20 November4 days later

Where to buy crocus for planting in Thunder Bay

Planting stock goes into the ground from 23 September to about 30 October; buy it before that. Within 15 km of Thunder Bay OpenStreetMap lists 2 garden centres and 1 market (collected 20 October 2026).

Places: © OpenStreetMap contributors, ODbL.

Questions

When to plant crocuses in Thunder Bay?

In Thunder Bay, crocus: plant from 23 September to about 30 October. Bulbs are best planted early in the window: late-planted bulbs may flower later or less well. Late planting works only while the soil can be dug. Mulch after planting.

When is the last spring frost in Thunder Bay?

Last spring frost around 11 May, first autumn frost around 23 October.

Other crops in Thunder Bay, with their dates