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When to plant hyacinths in Denver: 15 September – 14 December

In Denver, hyacinth: plant from 15 September to about 14 December. For planting stock, the places nearby include Plant Garage (garden centre, 1 km) and Planted (garden centre, 4 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).

Hyacinth in Denver: soil, season and weather

Nights then average below 0 °C in November–March; the coldest, January, averages -9 °C.

Planting15 September – 14 December
First autumn frost15 October
Coldest nightsJanuary, -9 °C
Soil back at 1 °C in spring11 February
Daylight12:30 on 15 September
Daylight at the winter solstice9:21

The same dates in Denver hold for Garlic, Tulip, Daffodil and Crocus.

Hyacinth in Denver: depth, winter cold, pests and pets

Plant hyacinths 10 cm deep, at least 7.5 cm apart (RHS). In the ground hyacinths are fully hardy, but in containers they can be frost tender in cold winters (RHS); here winter nights average below 0 °C, so wrap the pots or move them to a sheltered spot.

In Denver the average daily temperature stays at 10 °C or lower for about 26 weeks a year (our estimate from ten years of monthly weather). For this bulb Wisconsin Horticulture Extension gives a cold period of 12–15 weeks at about 2–10 °C. The winter here gives that in the ground, so the bulbs need no pre-chilling.

Flowers get smaller in the years after planting: for full spikes, replace the bulbs or add a few new ones each autumn (RHS).

If squirrels are a problem, protect the bulbs with wire mesh (RHS). Hyacinths are toxic to dogs, cats and horses: intense vomiting and diarrhoea (ASPCA).

Sources: RHS, Wisconsin Horticulture Extension, ASPCA.

Hyacinth in nearby cities

Around Denver, Cheyenne is 2 days earlier and Dodge City 14 days later.

CityDistanceDateDifference
Fort Collins90 km21 September – 5 December6 days later
Cheyenne156 km13 September – 4 December2 days earlier
Pueblo168 km28 September – end of December13 days later
Grand Junction316 km27 September – 7 December12 days later
Santa Fe (United States)458 km26 September – 11 December11 days later
Dodge City484 km29 September – end of December14 days later

Where to buy hyacinth for planting in Denver

Planting stock goes into the ground from 15 September to about 14 December; buy it before that. Within 15 km of Denver OpenStreetMap lists 28 garden centres, 2 plant nurseries, 11 markets and 5 farm shops (collected 7 October 2026).

Places: © OpenStreetMap contributors, ODbL.

Questions

When to plant hyacinths in Denver?

In Denver, hyacinth: plant from 15 September to about 14 December. 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 Denver?

Last spring frost around 1 May, first autumn frost around 15 October.

Other crops in Denver, with their dates