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When to plant crocuses in Helena: 3 September – 5 November

In Helena, crocus: plant from 3 September to about 5 November. For planting stock, the places nearby include Keeping It Green (plant nursery, 1 km); addresses and opening hours are below.

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 Helena: soil, season and weather

Nights then average below 0 °C in November–April; the coldest, February, averages -11.5 °C.

Planting3 September – 5 November
First autumn frost3 October
Coldest nightsFebruary, -11.5 °C
Soil back at 1 °C in spring27 March
Daylight13:15 on 3 September
Daylight at the winter solstice8:34

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

Crocus in Helena: 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 Helena 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 Helena, Calgary is 2 days earlier and Boise 24 days later.

CityDistanceDateDifference
Missoula155 km6 September – 12 November3 days later
Billings287 km14 September – 23 November11 days later
Idaho Falls345 km14 September – 14 November11 days later
Spokane425 km15 September – 23 November12 days later
Boise466 km27 September – end of December24 days later
Calgary517 km1 September – 26 October2 days earlier

Where to buy crocus for planting in Helena

Planting stock goes into the ground from 3 September to about 5 November; buy it before that. Within 15 km of Helena OpenStreetMap lists 2 farm-supply shops and 6 plant nurseries (collected 28 October 2026).

Places: © OpenStreetMap contributors, ODbL.

Questions

When to plant crocuses in Helena?

In Helena, crocus: plant from 3 September to about 5 November. 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 Helena?

Last spring frost around 19 May, first autumn frost around 3 October.

Other crops in Helena, with their dates