Best plants for Longmont gardens
Longmont gardens sit at about 4,980 ft in USDA zone 5b–6a on alkaline clay, with roughly 15 inches of precipitation and a last frost from late April into mid-May. Emerald ash borer is established here, and the city — running its own water utility — expanded its lawn-replacement rebates for 2026, so the plants below are water-wise, hardy, and ash-free.
Last updated 2026-05-31
Longmont growing conditions
- USDA hardiness zone
- 5b–6a (transitional)
- Elevation
- 4,980 ft
- Avg. annual precipitation
- ~15 in
- Soil
- alkaline clay
- Avg. last spring frost
- late April–mid May
- Avg. first fall frost
- late September–mid October
- Growing season
- ~150 days
Longmont straddles the Boulder–Weld county line on the plains where St. Vrain Creek and Left Hand Creek leave the foothills, at about 4,980 ft. It runs its own municipal water utility, and because it sits a few miles out from the mountain front it gets less of Boulder's brutal chinook wind while keeping the same heavy alkaline clay. Riverside and Union Reservoir-area neighborhoods can hold a little more soil moisture; the rest is dry plains. Crucially, Longmont is inside the Boulder County emerald ash borer zone, so tree diversity is not optional here.
What's challenging in Longmont
Emerald ash borer is established
Longmont sits within the Boulder County EAB infestation, with confirmed beetle activity in town. Don't plant new ash (genus Fraxinus); the city's forestry division (303-651-8446) and a certified arborist can advise on treating or removing an existing ash. The trees below are diverse non-ash alternatives. (source)
A rare expanded rebate for 2026
Unlike most Front Range programs that shrank or filled in 2026, Longmont expanded its lawn-replacement and Garden In A Box capacity this year using Colorado state matching grants — so there is more room than usual to get paid to convert turf. Apply early in spring before it fills. (source)
Plains cold, plains wind
Out on the plains Longmont swings colder than foothills Boulder and dries fast in spring wind; lean on hardy, established-water-wise plants and hold tender annuals until mid-May.
Top trees for Longmont
Ranked for Longmont's hail, drying wind, low water use and late frosts and cold.
Juniper — One – SeedJuniperus monosperma
Juniper — Rocky MountainJuniperus scopulorum
Pine — 'Vanderwolf's Pyramid'Pinus flexilis
Pine — Bristlecone(foxtail)Pinus aristata
Douglas-fir — Rocky Mountain Douglas firPseudotsuga menziesii var. glauca
Fir — WhiteAbies concolor
Spruce — ColoradoPicea pungens
Spruce — Colorado Blue – BABY BLUE®, 'Baby Blue Eyes', 'Bakeri', 'Fastigiata', 'Fat Albert', 'Hoopsi', 'Colorado Weeping', 'Sester Dwarf'Picea pungens glauca
Top shrubs for Longmont
Ranked for Longmont's hail, drying wind, low water use and late frosts and cold.
Top perennials for Longmont
Ranked for Longmont's hail, drying wind, low water use and late frosts and cold.
Top groundcover for Longmont
Ranked for Longmont's hail, drying wind, low water use and late frosts and cold.
Rebates & water rules in Longmont
Longmont water customers; applications open seasonally (spring)
Watering rules: As of 2026, voluntary conservation (no mandatory restrictions): water ≤2 days/week, only before 10 a.m. or after 6 p.m. Check the city for the current level. current rules →
Statewide: new Colorado turf rules (SB24-005/HB25-1113) limit nonfunctional turf in new development, and HOAs can't ban xeriscaping (SB23-178). Read the statewide rules →
Local resources near Longmont
- Extension
Boulder County CSU Extension — Master Gardeners — Serves Longmont; free plant, pest, and soil advice. - Native plant society
Colorado Native Plant Society — Northern Chapter — Native-plant programs covering the Longmont area.
When to plant in Longmont
Plant in spring (late April–May) or early fall, amend the clay, and apply for the lawn-replacement rebate early in the season before the expanded 2026 capacity fills. Water new plantings deeply through the dry, windy spring. Between the St. Vrain creeks, Longmont's plains beds warm a touch earlier than the foothills.
Video
Longmont gardening FAQ
- What hardiness zone is Longmont?
- Longmont is a transitional USDA zone 5b–6a at about 4,980 ft.
- Should I plant an ash tree in Longmont?
- No — emerald ash borer is established in Boulder County. Plant a diverse non-ash species and consult a certified arborist about existing ash.
- Is there a lawn rebate in Longmont?
- Yes — Longmont offers Resource Central lawn-replacement and Garden In A Box discounts, with expanded capacity for 2026 via state matching funds. Sign up early in spring; confirm current terms with Longmont Water Conservation.
- When is the last frost in Longmont?
- Roughly late April to mid-May; out on the plains a late freeze is common, so wait for warm soil before setting out tender annuals.
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