What to plant in December in Colorado
In Colorado (CO), December sits about 20 weeks before the average last frost (May 5). The state averages 149 frost-free days a year (last frost May 5, first frost October 1; USDA zones 3b, 4b, 5a, 5b, 6a, 7a).
Almost nothing is due to be sown in December - it's a month for planning, ordering seed and looking after what's already growing.
Dates here come from Colorado frost dates (last frost May 5, first frost Oct 1). For one crop in detail, see when to plant tomato, lettuce or garlic in Colorado.
Colorado covers a very wide range of climates, so dates near you can be two weeks or more either side of these. Enter your ZIP code in the planting calendar for dates tuned to your town.
Colorado: planting activity through the year
Planting dates for popular crops in Colorado
Every crop has its own full-year dates for Colorado: indoor start, transplant or direct sowing, and harvest.
Spring bulbs to plant in December in Colorado
Late September is preferred and September and October are the best months. Bulbs planted after October may not root well enough to flower evenly in spring. (Colorado State University Extension) ↗
A planning month: December garden jobs in Colorado
- Order seed while stock is good. Colorado's average last frost is May 5, so the first indoor sowings begin around February 10 - see starting seeds indoors.
- Sketch this year's beds and move each crop family to a new spot - the garden planner and the crop rotation guide make it quick.
- Test old seed: roll ten seeds in a damp paper towel for a week. If fewer than seven sprout, sow thicker or buy fresh.
- If the ground isn't frozen, spread compost now so it's worked in by spring, and send off a soil test - December is when labs are quiet.
USDA zone chart for Colorado
Colorado spans USDA zones 3b, 4b, 5a, 5b, 6a, 7a. Colder zones, usually higher or further inland, have a later last spring frost and an earlier first fall frost than the state average.
Questions gardeners ask
What vegetables can I plant in Colorado in December?
Very little is sown outdoors in Colorado in December. Use the month to plan beds, order seed and prepare soil.
Is it too late to plant tomatoes in Colorado in December?
For this year, yes - the tomato windows in Colorado have closed. The next step is to start seeds indoors from about March 10.
Is it too late to plant lettuce in Colorado in December?
For this year, yes - the lettuce windows in Colorado have closed. The next step is to start seeds indoors from about March 31.
When is the first frost in Colorado?
The statewide average first fall frost is around October 1 and the last spring frost around May 5. Colorado covers a wide range of climates, so local dates can differ by two weeks or more - look yours up by ZIP code.
When should I plant spring bulbs in Colorado?
Late September is preferred and September and October are the best months. Bulbs planted after October may not root well enough to flower evenly in spring. (Colorado State University Extension). See the bulb planting guide for depth and spacing.
What to plant in December in other states
Dates are computed from Colorado’s statewide average frost dates (from NOAA/NCEI climate normals) and each crop’s timing in our crop database. Your garden may be a week or two either side - for dates tuned to your ZIP code, use the planting calendar.