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Planting zones · Fort Collins & Boulder, Colorado

What Planting Zone Is Fort Collins & Boulder?

Fort Collins & Boulder is in USDA zone 5b–6a. Two northern Front Range cities at 5,000–5,500 ft. Boulder is wetter and snowier (about 21 in. of precipitation and 93 in. of snow) than Fort Collins (about 16 in.), and both average a last spring frost in early May.

  • USDA zone (2023)5b–6a
  • Coldest night (avg.)-15 to -10°FZIP 80521
  • Median last frostMay 232°F
  • Median first frostOct 732°F
  • Annual precipitation16 inches
  • Frost-free season157 days

Fort Collins & Boulder hardiness zone by ZIP code

On the 2023 USDA Plant Hardiness Zone Map, the ZIP codes we sampled in Fort Collins & Boulder fall in zones 5b to 6a; 80521 (zone 5b) has an average annual extreme minimum of -15 to -10°F. Choose perennials, shrubs, and trees rated at least to zone 5.

2023 USDA zone for sampled Fort Collins & Boulder ZIP codes
ZIPZoneAvg. coldest night
803026a-10 to -5°F
803036a-10 to -5°F
805015b-15 to -10°F
805215b-15 to -10°F
805255b-15 to -10°F

Not listed? Look up any ZIP code.

Frost dates and when to plant

The median last spring frost (32°F) at Fort Collins (CSU) is May 2 and the median first fall frost is Oct 7, a typical frost-free season of about 157 days.

Plant container perennials and shrubs after the median last frost (May 2), or in early fall at least six weeks before the median first frost (Oct 7) so roots can settle in before the ground freezes.

Rainfall and heat in Fort Collins & Boulder

Average annual precipitation is 16 inches (Fort Collins (CSU), 1991–2020), spread across the year with May the wettest month and January the driest.

The average high in July is about 87°F and the average low in January is about 18°F, measured at about 5,000 ft.

That is why a zone rating alone isn't enough for a xeriscape here: pick plants that are both cold-hardy to zone 5 and rated very low or low water once established.

Low-water plants for Fort Collins & Boulder

65 plants in our database are hardy to zone 5 and suited to zone 5. Here are 12, driest first, across plant types.

See all zone 5 plants

Frequently asked questions

What planting zone is Fort Collins & Boulder?

Fort Collins & Boulder, CO is in USDA hardiness zone 5b–6a on the 2023 USDA Plant Hardiness Zone Map, based on the ZIP codes we sampled (80302: 6a, 80303: 6a, 80501: 5b, 80521: 5b, 80525: 5b). In 80521, the average coldest night of the year is -15 to -10°F.

When is the last frost in Fort Collins & Boulder?

The median last spring frost (32°F) at Fort Collins (CSU) is May 2 and the median first fall frost is Oct 7, a typical frost-free season of about 157 days.

How much rain does Fort Collins & Boulder get?

Average annual precipitation is 16 inches (Fort Collins (CSU), 1991–2020), spread across the year with May the wettest month and January the driest.

Sources

  1. NOAA NCEI U.S. Climate Normals 1991–2020, Fort Collins (CSU) (USC00053005). ncei.noaa.gov
  2. NOAA NCEI U.S. Climate Normals 1991–2020, Boulder (USC00050848). ncei.noaa.gov
  3. USDA ARS 2023 Plant Hardiness Zone Map, by ZIP. planthardiness.ars.usda.gov