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 spring wind dries things fast, so the plants below are water-wise, hardy, and ash-free.
Last updated 2026-05-31
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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 to mid May
- Avg. first fall frost
- late September to 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)
Lawn replacement runs through Resource Central
Longmont's help with converting a lawn comes through Resource Central's Lawn Replacement Program: a 200 sq ft minimum, and at least half the new area has to be plants. The 2026 round is full, and Resource Central says applications reopen in spring 2027, so winter is the time to sketch the plan and plant list and apply as soon as it opens. (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.
One-seed JuniperJuniperus monosperma10 to 20 ftlow waterColorado nativeUSDA 3 to 8
Rocky Mountain Juniper (species)Juniperus scopulorum15 to 30 ftlow waterColorado nativeUSDA 3 to 8
'Vanderwolf's Pyramid' PinePinus flexilis25 to 30 ftlow to medium waterColorado nativeUSDA 4 to 7
Bristlecone (foxtail) PinePinus aristata15 to 30 ftlow to medium waterColorado nativeUSDA 4 to 7
Colorado Blue SprucePicea pungens glauca15 to 50 ftmedium to high waterColorado nativeUSDA 2 to 7
Colorado SprucePicea pungens50 to 75 ftmedium to high waterColorado nativeUSDA 2 to 7
Rocky Mountain Douglas firPseudotsuga menziesii var. glauca40 to 80 ftmedium waterColorado nativeUSDA 4 to 6
White FirAbies concolor50 to 80 ftmedium waterColorado nativeUSDA 3 to 7
Top shrubs for Longmont
Ranked for Longmont's hail, drying wind, low water use and late frosts and cold.
Apache plumeFallugia paradoxa4 to 6 ftlow waterColorado nativeUSDA 4 to 9
Big sagebrushArtemisia tridentata3 to 8 ftlow waterColorado nativeUSDA 3 to 9
Cliff fendlerbushFendlera rupicola3 to 6 ftlow waterColorado nativeUSDA 5 to 8
CliffrosePurshia mexicana4 to 8 ftlow waterColorado nativeUSDA 4 to 8
Common juniperJuniperus communis2 to 4 ftlow waterColorado nativeUSDA 2 to 7
Curlleaf mountain mahoganyCercocarpus ledifolius10 to 20 ftlow waterColorado nativeUSDA 3 to 8
Dwarf wild indigoAmorpha nana1 to 2 ftlow waterColorado nativeUSDA 4 to 9
FernbushChamaebatiaria millefolium4 to 6 ftlow waterColorado nativeUSDA 4 to 8
Top perennials for Longmont
Ranked for Longmont's hail, drying wind, low water use and late frosts and cold.
Bee Balm/HorsemintMonarda fistulosa24 inlow waterColorado nativeUSDA 3 to 9
Bigelow's TansyasterMachaeranthera bigelovii24 to 48 inlow waterColorado nativeUSDA 4 to 8
Black-eyed SusanRudbeckia hirta24 inlow waterColorado nativeUSDA 3 to 9
BlanketflowerGaillardia aristata12 inlow waterColorado nativeUSDA 3 to 10
Blue FlaxLinum lewisii18 inlow waterColorado nativeUSDA 4 to 9
Blue Mist PenstemonPenstemon virens12 inlow waterColorado nativeUSDA 3 to 8
Bush SunflowerHelianthus pumilus20 inlow waterColorado nativeUSDA 4 to 9
Butterfly MilkweedAsclepias tuberosa18 inlow waterColorado nativeUSDA 3 to 9
Top groundcover for Longmont
Ranked for Longmont's hail, drying wind, low water use and late frosts and cold.
Blue grama grassBouteloua gracilis8 to 18 inlow waterColorado nativeUSDA 3 to 10
Buffalo grassBouteloua dactyloides4 to 8 inlow waterColorado nativeUSDA 3 to 10
Mat penstemonPenstemon caespitosus2 to 4 inlow waterColorado nativeUSDA 3 to 8
Small-leaf pussytoesAntennaria parvifolia2 to 5 inlow waterColorado nativeUSDA 3 to 8
Sulfur buckwheatEriogonum umbellatum6 to 12 inlow waterColorado nativeUSDA 4 to 8
Clustered field sedgeCarex praegracilis8 to 18 inlow to medium waterColorado nativeUSDA 3 to 9
Aromatic asterSymphyotrichum oblongifolium12 to 24 inlow to medium waterColorado nativeUSDA 3 to 8
Creeping Oregon grapeMahonia repens10 to 18 inlow to medium waterColorado nativeUSDA 4 to 8
Rebates & water rules in Longmont
Longmont water customers; 200 sq ft minimum and at least 50% plant material. Resource Central's 2026 program is full and closed; it says applications reopen in spring 2027.
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 →
What's open right now across the Front Range, with dates and the rules that trip people up: lawn replacement rebates by city →
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 to May) or early fall, amend the clay, and if you want lawn-replacement help, apply as soon as Resource Central opens in spring, since it 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
Video PlantTalk Colorado: tree planting & care (CSU Extension)
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?
- Longmont takes part in Resource Central's Lawn Replacement Program, but the 2026 round is full. Resource Central says applications reopen in spring 2027. The city publishes no dollar figure, so confirm 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.
Plan your garden
Not sure what to plant? The finder matches Front Range trees, shrubs, perennials, and groundcover to your soil, water, sun, and zone.
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