Colorado Garden Guide: Planting Dates, Frost Dates & Growing Seasons
Colorado’s elevation swings create major frost differences—even nearby towns can have different planting windows.
In a typical year, the growing season in Colorado runs roughly from May 8 through October 5, giving many parts of the state about 150 frost-free days. Use this page as a statewide baseline, then compare local city pages for more precise planting timing.
Growing Season Snapshot
Colorado gardeners often find that elevation, dryness, and overnight temperature loss shape outcomes more than average frost dates suggest. A site can feel warm in full sun all day and still give back that heat quickly after dark, so maturity fit and local exposure often matter more than the calendar alone.
These season boundaries are climate normals, not a forecast. A 50% frost date means a 32°F frost arrives by that date in about half of years — and later in about half. Treat these dates as planning anchors, not guarantees.
Colorado Planting Calendar
A practical guide to when planting usually works in Colorado. These windows are based on climate normals (not a forecast) and line up with the 50% last spring frost and typical early-season heat.
| Crop | Planting Window | Method |
|---|---|---|
| Cool-season / early window Cold-tolerant crops that usually handle cooler spring conditions better. | ||
| Peas | April 10 – April 24 | direct sow |
| Spinach | April 10 – April 24 | direct sow |
| Lettuce | April 17 – May 1 | direct sow / transplant |
| Strawberries | April 17 – May 1 | plant crowns / transplants |
| Carrots | April 17 – May 1 | direct sow |
| Beets | April 17 – May 1 | direct sow |
| Radishes | April 10 – April 24 | direct sow |
| Potatoes | April 24 – May 8 | plant seed potatoes |
| Onions | April 17 – May 1 | sets / transplants |
| Garlic | April 19 – April 29 | plant cloves |
| Broccoli | April 24 – May 8 | transplant |
| Cauliflower | April 24 – May 8 | transplant |
| Cabbage | April 24 – May 8 | transplant |
| Kale | April 14 – May 4 | direct sow / transplant |
| Swiss chard | April 18 – May 8 | direct sow / transplant |
| Main warm-season window Crops that usually do best once frost risk fades and the season starts opening up more fully. | ||
| Beans | May 8 – May 22 | direct sow |
| Sweet corn | May 13 – May 23 | direct sow |
| Cucumbers | May 17 – May 27 | direct sow / transplant |
| Zucchini | May 17 – May 27 | direct sow / transplant |
| Squash | May 17 – May 27 | direct sow / transplant |
| Melons | May 17 – May 27 | direct sow / transplant |
| Watermelons | May 17 – May 27 | direct sow / transplant |
| Basil | May 17 – May 27 | direct sow / transplant |
| Tomatoes | May 17 – May 27 | transplant |
| Peppers | May 24 – June 3 | transplant |
How to use this: aim for the earlier part of each window for the most reliable results. Later planting can still work, but it usually depends more on variety maturity, warmer microclimates, and simple protection like row cover or low tunnels.
Common Timing Mistakes
These patterns show up again and again in Colorado — especially in typical years.
- Waiting too long after last frost to plant warm-season crops, which compresses harvest timing.
- Assuming conditions are uniform across the region — frost timing often varies widely by elevation, exposure, and shelter.
- Relying on calendar dates instead of crop maturity and typical frost timing.
Frost Dates and Growing Conditions Across Colorado Cities
Growing conditions often vary more within Colorado than most gardeners expect. Differences in elevation, exposure, cold-air drainage, and nearby pavement or buildings can shift frost timing and change how much usable season you really have.
| City | Last spring frost | First fall frost | Frost-free days | Remaining GDD (May 15 → Aug 1, base 50) |
|---|---|---|---|---|
| Fort Collins | May 03 | Oct 06 | 156 | 2477 → 1074 |
| Greeley | May 02 | Oct 08 | 159 | 2859 → 1270 |
| Loveland | May 12 | Oct 01 | 142 | 2120 → 923 |
| Pueblo | Apr 26 | Oct 13 | 170 | 3113 → 1384 |
| Colorado Springs | May 03 | Oct 08 | 158 | 2446 → 1071 |
| Grand Junction | Apr 14 | Oct 23 | 192 | 3482 → 1549 |
| Durango | May 28 | Sep 30 | 125 | 382 → 143 |
| Montrose | May 20 | Oct 01 | 134 | 1372 → 569 |
| Sterling | Apr 30 | Oct 09 | 162 | 2921 → 1262 |
| Denver | Apr 30 | Oct 12 | 165 | 3003 → 1351 |
| Boulder | May 06 | Oct 05 | 152 | 2479 → 1116 |
| Longmont | May 07 | Oct 05 | 151 | 2473 → 1077 |
| Alamosa | May 30 | Sep 17 | 110 | 1432 → 576 |
- Frost timing varies widely across the region, especially between colder pockets and more sheltered sites.
- Earlier-frost and shorter-season locations usually need faster-maturing crops and tighter planting timing.
- Warmer locations usually retain more remaining heat through the season, giving longer-season crops and later plantings better odds of finishing.
- Urban areas, walls, and sheltered gardens usually stay warmer than open rural or wind-exposed sites.
- Cold air settles in low spots, so slightly elevated beds often avoid the earliest frosts.
- South- and west-facing areas usually warm sooner in spring and can stay productive later into fall.
How the Growing Season Works in Colorado
Colorado is mostly a timing-and-variety season. Reliable results usually come from planting on time, matching maturity to the frost window, and making good use of the remaining summer heat.
- Start on time: early establishment is often the biggest controllable factor for warm-season success.
- Match crops to the window: dependable harvests usually come from realistic maturity timing, not optimistic timing.
- Use late summer well: fast greens, roots, and compact crops are often the best fit for a second round.
Microclimate note: frost timing varies widely across Colorado, so sheltered gardens, urban sites, and warmer exposures can behave very differently from colder open areas.
Late-summer note: there is often still meaningful heat left around early August, so second plantings of faster crops can still be worthwhile.
Remaining Season Heat in Colorado (Base 50 GDD)
Growing Degree Days (Base 50°F) measure heat accumulation. “Remaining GDD” shows how much usable heat is typically still available from a given date onward in a normal season.
| Planting date | Base | Typical GDD still available |
|---|---|---|
| May 15 | 50 | 2446 |
| June 1 | 50 | 2286 |
| July 1 | 50 | 1787 |
| August 1 | 50 | 1071 |
Use these values to judge whether a crop or variety still has enough heat left after planting. This is especially helpful for later sowings, shorter-maturity choices, and deciding whether a second round is realistic.
How Gardeners Adapt
Experienced gardeners in Colorado usually adjust their timing and crop choices to match how the season actually behaves, not just the calendar.
- Planting warm-season crops promptly once frost risk fades.
- Using row cover or low tunnels to smooth out temperature swings early and late in the season.
- Succession planting fast crops to keep beds productive through summer.
- Watching local conditions closely and adjusting timing year by year.
Colorado Garden Planning Chart
A practical “typical year” for planning. Use it as a baseline, then adjust for microclimates and variety maturity.
| Stage | What it usually means |
|---|---|
| Early season | Start cold-tolerant crops, prep beds, and pay more attention to soil warmth and night temperatures than to the calendar alone. |
| Main planting | Around May 8, the main planting push usually begins as frost risk fades. Warm-season crops generally perform best when they get established promptly. |
| Peak growth | This is when water, fertility, spacing, and pest pressure have the biggest effect on final yield. |
| Late-summer decisions | There is often enough late-season heat left for a meaningful second round of quick crops. |
| Finish window | Plan to have frost-sensitive crops mostly wrapped up by October 5. Cooling nights often slow crops before the first real frost arrives. |
Typical season length: 150 frost-free days between the median spring and fall frost dates.