What to plant in September in Colorado
In Colorado (CO), September sits about 2 weeks before the average first fall frost (October 1). 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).
1 crop has a sowing or planting window this month: radish - and 1 of those windows close during September.
Dates here come from Colorado frost dates (last frost May 5, first frost Oct 1). For one crop in detail, see when to plant radish, tomato or lettuce 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
Last chance in September
Radish (sow for a fall crop, by Sep 3)
For fall and winter harvests (1)
Sowings counted back from Colorado's first fall frost, so the crop matures before the cold - or, for garlic and similar, planted after it.
| Crop | What to do | Window | This month |
|---|---|---|---|
| Radish | Sow for a fall crop | Aug 17 – Sep 3 | Last chance - ends Sep 3 |
Harvesting in September
First harvests expected this month from crops sown or planted on time earlier in the season.
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 September 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) ↗
Fall garden season: September garden jobs in Colorado
- The average first frost is October 1, about 2 weeks away. Pick tender crops (tomatoes, peppers, squash, beans) before it, or cover them on cold nights.
- Still time to sow or plant: radish. Fast greens and radishes are the safest bets this late.
- Row cover buys 4-6°F of frost protection and weeks of extra harvest - see season extension.
- Pull finished crops and sow a cover crop (cereal rye or crimson clover) into empty beds before the soil gets cold.
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 September?
1 crops have a window in September: radish. The tables above give the exact dates for each.
Is it too late to plant garlic in Colorado in September?
Not too late - it's actually a little early. In Colorado the next garlic window opens around October 12: plant in fall, after first frost.
Is it too late to plant tomatoes in Colorado in September?
For this year, yes - the tomato windows in Colorado have closed. The next step is to start seeds indoors from about March 10.
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.
What can I harvest in Colorado in September?
From plantings made on time: leek, parsnip, salsify, pumpkin, rosemary, zucchini / summer squash, celery, celeriac, luffa (loofah gourd), cucumber.
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 September 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.