GreenlyWhat to plant in December in the Mountain West
Worked out for 15 cities from their own weather and frost dates, by zone.
What to sow and plant in December in the Mountain West, by zone: frost possible, highs of 50–61 °F (Pueblo and St. George): garlic, broad bean, peas, onion, spinach and 18 more; frost possible, highs below 50 °F (Denver, Salt Lake City and 11 more): garlic, cabbage, broccoli and flower bulbs.
In the Mountain West, December is winter.
Frost possible, highs of 50–61 °F: Pueblo and St. George
In December, on average, these cities have highs of 50 to 53 °F and lows of 25 to 33 °F, 0.4 to 1.1 in of rain on 3 to 4 days; the day lasts 9 h 31 min to 9 h 38 min (on the 15th). A dry month: whatever is sown needs watering.
December falls in the frost season: frost-tender crops wait.
| How | What | Where |
|---|---|---|
| plant cloves | Garlic | all |
| start indoors, plant out in January or sow direct | Broad bean, spinach | all |
| sow direct | Peas, radish, Swiss chard, arugula, chamomile, daikon, kale, parsnip, turnip | St. George |
| plant sets | Onion, shallot | St. George |
| start indoors, plant out in January | Lettuce, cauliflower, beet | St. George |
| start indoors, plant out in February or sow direct | Cabbage | all |
| start indoors, plant out in February | Broccoli | Pueblo |
| start indoors, plant out in February | Parsley, Brussels sprouts | all |
| start indoors, plant out in January | Kohlrabi | all |
| plant bulbs | Crocus, daffodil, hyacinth, tulip | Pueblo |
Compared with November: no longer sown — carrot, leek, cilantro, dill and mustard greens.
Not starting in December: tomato (March, started indoors), bell pepper (March, started indoors), zucchini (April, started indoors) and green beans (May, sown direct) — dates for Pueblo.
Ready to harvest in December in Pueblo, if sown in the right month: peas (October), lettuce (October), radish (November), carrot (October), Swiss chard (October), beet (October), parsley (October) and cilantro (October).
Frost possible, highs below 50 °F: Denver, Salt Lake City, Colorado Springs, Reno and 9 more
In December, on average, these cities have highs of 33 to 46 °F and lows of 17 to 30 °F, 0.5 to 3.8 in of rain on 3 to 14 days; the day lasts 8 h 34 min to 9 h 28 min (on the 15th).
December falls in the frost season: frost-tender crops wait.
| How | What | Where |
|---|---|---|
| plant cloves | Garlic | Denver, Salt Lake City, Colorado Springs and 6 more |
| start indoors, plant out in January | Broad bean, spinach | Denver, Colorado Springs and Reno |
| start indoors, plant out in February | Cabbage, broccoli | Denver, Salt Lake City, Colorado Springs and 4 more |
| plant bulbs | Crocus, daffodil, hyacinth, tulip | Denver, Salt Lake City, Colorado Springs and 6 more |
Compared with November: no longer sown — peas, onion, radish, arugula and turnip.
Not starting in December: tomato (April, started indoors), bell pepper (April, started indoors), zucchini (May, started indoors), green beans (June, sown direct), lettuce (February, started indoors) and peas (April, sown direct) — dates for Cheyenne.
Ready to harvest in December in Cheyenne, if sown in the right month: broad bean (September), peas (October), spinach (October), lettuce (October), radish (November), chayote (July), luffa (July) and turnip (October).
- Frost dates in Denver
- Frost dates in Salt Lake City
- Frost dates in Colorado Springs
- Frost dates in Reno
- Frost dates in Billings
- Frost dates in Cheyenne
- Frost dates in Helena
- Frost dates in Carson City
- Frost dates in Fort Collins
- Frost dates in Grand Junction
- Frost dates in Missoula
- Frost dates in Elko
- Frost dates in Provo
How we work it out
For each city we use its average weather in December and the months after (highs, lows and rain for 2016–2025, ERA5 reanalysis via Open-Meteo) and its average frost dates. A crop starts in December if the month's mean temperature reaches the minimum soil temperature for germination on its card (we use the mean air temperature as a stand-in for the soil's) and if, over its first months (up to three), the average highs stay within its group's range, with no frost for crops that cannot take it. Crops started indoors count from the month they are planted out.
Temperature groups from Colorado State University Extension: cool-season crops prefer 60–80 °F and lose quality in heat; hardy ones grow in days as cool as 40 °F, semi-hardy ones from 40–50 °F (we use 50 °F); warm-season crops need days above 55 °F, and the most tender (tomato, pepper, eggplant, melon, watermelon, squash) above 60 °F, up to 95 °F. Crops the guide does not name go into the stricter group by their frost hardiness. Fava (broad) beans, which the guide does not name, count as hardy: hardy varieties are sown in fall and overwinter (RHS). Garlic and bulbs: a month before the first frost, and later only while the ground is not frozen (as on each city's page).
This is a general rule from averages: your garden can be a week or two earlier or later, and a greenhouse or a cold frame brings the season forward. Greenly works out the dates for your location.
- Moon planting calendar for December 2026
- What to plant in December: all climates
- Gardening in the United States: guide by region
Other months in the Mountain West
- What to plant in December in the South
- What to plant in December in Texas
- What to plant in December in Florida
- What to plant in December in California
- What to plant in December in the Pacific Northwest
- What to plant in December in the Southwest
- What to plant in December in the UK
- What to plant in December in Ireland
