Generally — Most Areas
Irish moss (zones 4-8) partially overlaps with Colorado (3a-7a). It can grow in zones 4-7 within the state.
Zone Comparison
Irish Moss Needs
- USDA Zones: 4-8
- Soil pH: 5.5 - 7.5
- Sun: Part Sun
- Drainage: well (dry spells)
- Frost-Free Days: 120+
Colorado Has
- USDA Zones: 3a-7a
- Last Frost: Apr 15 - Jun 15
- First Frost: Aug 25 - Oct 15
- Annual Rainfall: 7-20 inches
- Common Soils: Sandy loam, Clay loam, Alkaline caliche
Plant Zone Range (zones 4-8)
Preferred Soil pH
Plant data: USDA PLANTS Database / plant_species_v5.csv. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
Growing Season Fit
Zone compatibility says you can survive winter here. Whether the growing season is long enough — and warm enough — is a different question.
Frost-free days
Irish Moss wants 120+ frost-free days; a typical Colorado site sees ~190 (NOAA Climate Normals). That leaves comfortable headroom for succession planting.
Climate aggregates derive from USDA NRCS county-level hardiness data + Cornell CALS Extension GDD-by-region tables + MSU Extension chill-hours-by-zone (1991-2020 NOAA Climate Normals baseline).
Soil + Drainage Fit
Irish Moss likes near-neutral soil (pH 5.5-7.5). That's the common-ground band across Colorado's sandy loam and clay loam — a soil test confirms it for your site. Drainage matters: this plant wants well (dry spells). If your Colorado site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Plant pH and drainage requirements from USDA PLANTS Database. Colorado soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Irish Moss in Colorado — Quick Answer
- Verdict: Generally — Most Areas
- Plant Zones: 4-8 (USDA PLANTS Database)
- State Zones: 3a-7a (USDA ARS PHZM 2023)
- Growing Season: Apr 15 - Jun 15 to Aug 25 - Oct 15 (NOAA Climate Normals)
What Else to Consider
Zone compatibility tells you about winter cold survival — but Colorado growers also need to think about:
Low annual rainfall (7-20 inches) means irrigation is essential nearly everywhere
High altitude UV and temperature swings stress plants
Very short growing season at elevation (60-90 frost-free days above 8,000 ft)
Alkaline soils (pH 7.5-8.5) limit acid-loving plants without amendment
Pollinator + Wildlife Value
Irish Moss draws pollinators (low value, USDA PLANTS Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Deer pressure is meaningful across much of Colorado; irish moss is listed as deer-resistant (USDA PLANTS Database), which makes it a safer pick for unfenced sites.
Colorado Cooperative Extension
For Colorado-specific cultivar recommendations, planting calendars, and pest pressure for irish moss, the canonical source is Colorado State University Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Check your specific parcel in Colorado
State-level data is a sketch. Your Growable Ground report scores irish moss against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
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