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By S. Carter, N. Goeckner, C. Julian (CSFS), L. Langelo, I. Shonle and C. Dennis (Emeritus CSFS) (4/23)

Quick Facts…

  • The right plants around structures are important for wildfire safety.
  • Management of defensible space and plant types is essential.
  • This fact sheet is one of a series of three.
  • Plants rated 10 have the least flammability.
  • This fact sheet recommends low flammability plants for zones 1 and 2.
  • Refer to the Colorado State Forest Service’s Home Ignition Zone guide for further details on home ignition zones.


In Colorado, in the wildland-urban interface (WUI), it isn’t a matter of if a wildfire will impact residences and properties, but when. The WUI includes any areas where structures and other human developments meet or intermingle with wildland vegetative fuels, including grasses, shrubs and trees. Wildfires are a natural part of Colorado’s varied ecosystems. Planning ahead and taking action to reduce the risk of wildfires can increase the likelihood a home survives when wildfires do occur. Firefighters do their best to protect residents, but ultimately, it’s your responsibility to protect your property and investments from wildfire.

This fact sheet is a part of a series of three publications created to help homeowners focus on actions that are effective in reducing wildfire hazards on properties. These efforts should always begin with the home or structure itself and progress outward. Defensible space is the area around a home or other structures that has been modified to reduce fire hazards by creating space between potential fuel sources.

In the defensible space, natural and man-made fuels are treated, removed or reduced to slow the spread of wildfire and alter fire behavior. Plants that are low flammability are selected for planting, especially closer to the home.

Creating an effective defensible space involves establishing a series of management zones. Develop these zones around each building, including detached garages, storage buildings, barns and other structures. Recognize that fuel continuity and density play a critical role in wildfire behavior. Zones are defined from the structure edge in feet:

  • Zone 1: 0-5 feet
  • Zone 2: 5-30 feet
  • Zone 3: 30-100 feet

This fact sheet covers plants in zones 1 and 2; a different publication; the Fire-Resistant Landscaping fact sheet, discusses plants in zone 3. For a defensible space plan for properties, contact the nearest Colorado State Forest Service field office or local CSU Extension office for guidance. Consult with a forester, fire department staff or community organization appropriately trained in wildfire mitigation practices.

Opuntia (Photo by I. Shonle)

Low-Flammability Plant Characteristics

Recommendations on this list are based on a methodology developed by Idaho Firewise in Boise, Idaho. The methodology rates the flammability of plants based on specific characteristics ranked on a scale of 0-10 with 0 the most flammable and 10 the least flammable. To create the highest degree of protection for structures, the recommendation is to plant only plants with scores of 8, 9 and 10 for zones 1 and 2 within the first 30 feet from the home. These species are the least flammable plants to plant near structures, but keep in mind that there are no truly “fireproof” plant species.

Existing vegetation with scores below an 8 (indicating more flammability) is addressed in the Fire-Resistant Landscaping fact sheet (6.303). Plants that have lower flammability and are more resistant to wildfire and plants that have a higher flammability and are less resistant to wildfire have these specific characteristics:

Attributes that decrease flammability

  • Low oil or resin content
  • High moisture content
  • Soap, latex or pectin content
  • Compact growth form
  • Green stems
  • Drought tolerant

Attributes that increase flammability

  • High oil or resin content
  • Low moisture content
  • Tall growth
  • Open form
  • Fine wood (twiggy) stems
  • High water need

Many plants are highly flammable during different seasons of the year. At such times, left unmanaged, they can accelerate the spread of a wildfire that can harm communities. All vegetation, naturally occurring and otherwise, is potential fuel for fire. Its type, amount and arrangement have a dramatic effect on fire behavior.

There are no “fireproof ” plant species. Plant choice, spacing and maintenance are critical to reduce the risk adjacent to the structure.

There are many concepts to consider when choosing low-flammability plants. A plant’s moisture content is the single most important factor governing its volatility. However, resin content and other factors in some species render them flammable even when the plant is well watered. Conifers tend to be flammable due to their oil and pitch content, regardless of their water content. Deciduous plants tend to be more fire resistant because their leaves have higher moisture content and their basic chemistry is less flammable. Also, when deciduous trees are dormant, there is less fuel to carry fire through their canopies.

In some cases, there is a strong correlation between drought tolerance and fire resistance. These plants offer less fuel or have a higher moisture content, both of which help reduce fire hazard. There also appears to be a correlation between a plant’s salt tolerance and natural fire resistance. Plants adapted to salty conditions, and actually growing in salty situations, may better resist burning.

Most of Colorado’s native vegetation is adapted to fire and is flammable. Common flammable plants have flammability scores less than 8. Common flammable trees are junipers, pines, firs and spruces. Common flammable shrubs are Gambel oak, three-leaf sumac and mountain mahogany. Planting of these species is discouraged adjacent to the home in defensible space zones 1 and 2. If they’re already present, consider replacing them with some of the recommended species included in this fact sheet. If you decide to keep a flammable plant in your landscape, keep it pruned and thinned, remove dead material regularly, and keep it at least 30 feet from any structure or other plants. See the Fire-Resistant Landscaping fact sheet (6.303) for more information on these mitigation measures.

Don’t Forget Maintenance

A landscape is a dynamic, constantly changing system. Plants considered “fire resistant” and that have low amounts of flammable vegetation can lose these characteristics over time. Your landscape, and the plants in it, must be maintained to retain their low-flammability properties. Maintenance is addressed in further detail in the Fire-Resistant Landscaping fact sheet (6.303).

Supporting Publications from CSU Extension, the Colorado State Forest Service, and Idaho Firewise

The following publications are available and are referenced. The CSFS Home Ignition Zone (HIZ) guide describes the concepts of structural ignitability and defensible space. Low-Flammability Landscape Plants (6.305) recommends fire-resistant plants for zones 1 and 2 identified in the defensible space section of the CSFS HIZ guide. Fire-Resistant Landscaping (6.303) recommends design features for zones 1, 2 and 3 and recommends plants with mitigation measure for plants and existing vegetation in zone 3.

The CSFS HIZ guide, Low-Flammability Landscape Plants and Fire-Resistant Landscaping are considered a package that can help with developing actions to reduce wildfire risk and impacts. The Idaho materials provided the basis for the addition of the flammability scoring and approach for this update.

  1. CSFS Home Ignition Zone Guide, 2021 (Replaces 6.302, Creating Wildfire-Defensible Zones)
  2. 6.303, Fire-Resistant Landscaping (Updated 2023)
  3. Idaho Firewise, Fire-Resistant Landscapes – Plant Materials
Rocky Mountain Penstemon (Photo by I. Shonle)

Key:Water needs:VL = very lowL = lowM = mediumH = high
Sun/Shade:S = sunPS = part sunSh = shade
Scientific NameCommon NameApprox.Water
Elevation(1,000 ft.)Approx.Bloom
Flowers and Ground Covers
Achillea lanulosaaNative yarrowL-HS/PS1.5 – 2′YYYYYJul
Achillea tomentosabWoolly yarrowM-HS/PS.5′YYNNNJul
Aconitum spp.cMonkshoodM-HS2′YYYYYJun-Jul
Aconitum columbianumacColumbian monkshoodM-HS2′YYYYYJun-Jul
Ajuga reptansbBugleweedHSh< .5′YYYYYJun-Jul
Alchemilla sp.Ladys mantleM-HPS/Sh1′YYYY?Jun-Jul
Allium cernuumacNodding onionL-HS/PS1′YYYYYJun
Allium geyeriacGeyer onionL-HS/PS1′YYYY?Jun
Anaphalis margaritaceaaPearly everlastingL-HS1.5 – 2.5′YYYY?Aug
Anemone blandaWindflowerM-HS/PS1′YYYY?Apr-May
Antennaria parvifoliaabSmall-leaf pussytoesMS/PS<.5′YYYYYJun
Antennaria roseaabRosy pussytoesMS/PS<.5′YYYYYJun
Aquilegia spp.ColumbineM-HS/PS1 – 2′YYYYYJun-Jul
Aquilegia coeruleaaColorado blue columbineM-HS/PS1 – 2′YYYYYJun-Jul
Aquilegia chrysanthaaYellow columbineM-HS/PS1 – 2′YYYYYJun-Aug
Arabis sp.bRockcressL-HS< 1′YYYYYMay-Jun
Armeria maritimaSea thriftL-HS/PS.5′YYYYYApr-Jun
Artemisia caucasicaCaucasian sageL-MS/PS1- 2′YYY??n/a
Artemisia frigidaacFringed sageL-MS1 – 1.5′YYYYYn/a
Artemisia ludovicianaaPrairie sageL-MS1 – 1.5′YYY??n/a
Aster laevisaSmooth asterL-HS/PS1 – 3′YYYY?Aug-Sep
Aster porteriaPorter asterL-MS1′YYY??Aug-Sep
Aubrieta sp.bFalse rockcressMS1′YYYYYApr-May
Aurinia sp.bBasket of goldMS/PS1′YYYYYApr-May
Calochortus gunnisoniiaMariposa lilyM-HS.5 – 2′YYYY?Jul-Aug
Campanula rotundifoliaaCommon harebellM-HS.5 – 1′YYYYYMay-Oct
Centranthus ruberJupiters beardL-HS/Sh2 – 2.5′YYYY?May-Oct
Cerastium strictumabMouse ear chickweedMS/PS1′YYYY?May-Jun
Cerastium tomentosumbSnow-in-summerL-MS/PS1′YYYYYMay-Jun
Claytonia lanceolataaSpring beautyMSh.5 – 1.5′YYY??Mar-Apr
Convallaria majalisbcLily-of-the-valleyHSh< 1′YYYY?May-Jun
Delosperma nubigenumbHardy yellow iceplantM-HS.5′YYY??Jun
Delphinium spp.cDelphiniumM-HS/PS.5 – 3’+YYYYYJun-Jul
Dianthus spp.PinksL-HS<.5′ – 2′YYYYYMay-Aug
Doronicum sp.Leopards baneHS/PS2 – 3′YYYY?Jul-Aug
Echinacea purpureaPurple coneflowerMS2 – 3′YYYYYJul-Aug
Epilobium angustifoliumFireweedHS/PS3′NYYYYJul-Aug
Erigeron flagellarisaWhiplash daisy, trailing fleabaneL-MS< 1′YY???Jun-Jul
Eriogonum umbellatumaSulphur flowerMS/PS<.5′YYYYYJun-Jul
Erysimum asperumaWestern wallflowerMS/PS1’+YYYY?Jun-Jul
Gaillardia aristataaBlanket flowerL-MS1 – 1.5′YYYYYJul-Sep
Galium borealeabNorthern bedstrawM-HSh<1′YYYYYMay-Jun
Geranium spp.Hardy geraniumsMSh/PS2′YYYYYMay-Oct
Geranium caespitosumaWild geraniumMSh/PS2′YYYYYMay-Oct
Geum triflorumPrairie smokeM-HS/PS1.5′YYY??Jun
Helianthella quinquenervisaAspen sunflowerMS1′???YY?
Helianthemum nummulariumRockroseM-HS< 1′YYY??May-Jun
Helianthus pumilusaSmall sunflowerMS1 – 2′YYY??Jun-Jul
Heuchera spp.Coral bellsM-HPS/Sh1 – 2′YYYYYJun-Aug
Ipomopsis aggregataaScarlet giliaMS/PS1 – 2′YYYYYJun-Aug
Iris germanicaBearded irisL-MS1 – 3′YYYYYMay-Jun
Iris missouriensisacMissouri or Native irisM-HS1 – 2′YYYYYMay
Lamium sp.bDead nettleM-HSh< 1′YYYY?May-Jun
Lavandula spp.LavenderL-MS1 – 2′YYY??Jun-Nov
Leucocrinum montanumaSand lilyL-MS< 1′YYY??May
Liatris punctataaDotted gayfeatherVL-LS1 – 2′YYYYYAug-Oct
Linum lewisiiacWild blue flaxL-HS/PS1 – 2′YYYYYMay-Sep
Lupinus argenteusacSilver lupineMSh/PS1 – 3′YYYYYJun-Jul
Mertensia lanceolataaNarrow-leaved chiming bellsM-HSh/PS1 – 2′YYYYYMay-Jun
Mimulus guttatusaYellow monkey-flowerHSh1′?YYYY?
Monarda fistulosaaNative beebalmM-HS/PS1 – 2′YYYYYJul-Oct
Oenothera caespitosaaWhite stemless evening primroseL-MS1 – 2′YYYYYJun-Aug
Papaver orientaleOriental poppyHS/Sh2 – 3′YYYYYMay-Jun
Penstemon caespitosusabMat penstemonL-MS< .5′YYYYYJun
Penstemon secundiflorusSidebellsL-MS1 – 2′YYYY?May-Jun
Penstemon teucrioidesaGermander penstemonL-MS.5′YYY??Jun-Jul
Penstemon virensacBlue mist penstemonMS/PS.5′YYYYYMay-Jun
Phlox subulataMoss phloxMS< .5′YYYYYMay
Polemonium sp.Jacobs ladderHS/PS1 – 2′YYYYYMay-Aug
Potentilla fissaaLeafy potentillaM-HPS1′YYYY??
Potentilla vernabSpring potentillaM-HPS< .5′YYYYYMar-May
Pulsatilla patensaPasque flowerMS/PS1′YYYYYMar-May
Ratibida columniferaaPrairie coneflowerL-MS2′YYYYYJul-Sep
Rudbeckia hirtaaBlack-eyed SusanM-HS2 – 3′YYYYYJul-Sep
Salvia officinalisCooking sageL-MS/PS2′YYYY?Jun
Saxifraga hirsutaSaxifrageHS/PS.5’+YYYYYMay-Jun
Scutellaria brittoniiaSkullcapMS/PS.5 – 1′YYYY?Aug-Sep
Sedum spp.bStonecropMS/PS1 – 1.5′YYYYYJul-Aug
Sedum lanceolatumaYellow stonecropMS/PS.5′YYYYYJul-Aug
Sempervivum sp.Hens and chicksL-MS/PS.5′YYYYYn/a
Senecio spartioidesacBroom groundselVL-LS2 – 3′YY???Sep-Oct
Solidago missouriensisaSmooth goldenrodL-MS1 – 2′YYYY?Jul-Aug
Thalictrum fendleriaFendler meadowrueHS/PS2 – 3′??YYYJul-Aug
Thermopsis divaricarpaaSpreading golden bannerM-HS/PS2′YYYY?May
Tradescantia occidentalisaWestern spiderwortMS/PS1.5′YYYY?Jun-Aug
Thymus spp.bThymeL-MS< .5′YYYYYJun-Jul
Veronica pectinataSpeedwellL-MS< .5′YYYYYApr-Jul
Vinca minorbPeriwinkle, myrtleHSh< 1′YYYY?Apr-Jun
Waldsteinia sp.bBarren strawberryM-HSh/PS< 1′YYYY?May-Jun
Arctostaphylos nevadensisabPinemat manzanitaMS/PS1 – 2′YYYNNn/a
Arctostaphylos patulaaGreenleaf manzanitaMS/PS3 – 4′YYYNNn/a
Arctostaphylos uva-ursiabKinnikinnick, bearberryMS/Sh1′YYYYYn/a
Betula glanulosaaBog birchHS/PS6 – 8′YYYYYn/a
Calluna sp.HeatherHS/PS2′YYY??Jul-Aug
Ceanothus fendleriaBuckbrush, mountain lilacMS2′YYY??Jul
Cercocarpus intricatusLittle-leaf mountain mahoganyVL-LS4 – 6′YYYY?n/a
Cercocarpus montanusacTrue mountain mahoganyL-MS4 – 6′YYYY?n/a
Chrysothamnus spp.aRabbitbrushVL-LS2 – 6′YYYYYJul-Aug
Cornus stoloniferaaRedtwig dogwoodHS/Sh4 – 6′YYYYYn/a
Cotoneaster horizontalisSpreading cotoneasterMS/PS2 – 3′YYYY?May-Jun
Daphne burkwoodiiBurkwood daphneMS/PS2 – 3′YYY??Apr-Jun
Erica sp.HeathHS/PS1′YYY??Jan-Mar
Euonymus alatusBurning bush euonymusMS/Sh1 – 6′YYY??n/a
Fallugia paradoxaaApache plumeVL-LS2 – 4′YYYYYJun-Oct
Holodiscus dumosusaOcean spray, cliff/rock spireaL-MS/PS4′YYYYYJun
Jamesia americanaaWax flowerM-HS/Sh2 – 6′YYYYYJun
Lonicera tataricaTatarian honeysuckleMS/PS4 – 6′YYYYYMay-Jun
Mahonia aquifoliumOregon grape hollyM-HS/Sh4 – 6′YYY??May-Jun
Mahonia repensabCreeping grape hollyL-HS/Sh1 – 2′YYYYYMar-May
Philadelphus microphyllusaLittle-leaf mockorangeMS2 – 3′YYYY?Jun
Physocarpus monogynusaMountain ninebarkMS/Sh2 – 4′YYYYYJun
Potentilla fruticosaaShrubby cinquefoilMS/PS2 – 3′YYYYYMay-Sep
Prunus besseyiaWestern sand cherryL-MS1 – 3′YYYY?May
Purshia tridentataaAntelope bitterbrushL-MS1 – 2′YYY??Jun-Aug
Ribes aureumaGolden currantMS/PS2 – 3′YYYYYApr-May
Rosa woodsiiaWoods’ or native wild roseMS/PS2 – 3′YYYYYJun-Jul
Shepherdia canadensisaRusset buffaloberryM-HS5 – 6′YYYYYn/a
Symphoricarpos spp.dSnowberry, coralberryMS/PS2 – 3′YYYYYn/a
Viburnum eduleaHighbush cranberryHS6 – 8′YYYYYMay-Jun
Yucca baccataaBanana or broad-leaf yuccaVL-LS/PS2 – 3′YYYNNJun
Yucca filamentosaAdams needleMS/PS2 – 3′YYYNNJun
Yucca glaucaaSpanish bayonet, small soapweed, Great Plains yuccaVL-LS/PS2 – 3′YYYY?Jun
Large Shrubs and Trees
Acer ginnalaGinnala mapleM-HS6 – 10′YYYYYn/a
Acer glabrumaRocky Mountain mapleM-HS/Sh6 – 10′YYYYYn/a
Acer grandidentatumaWasatch mapleMS/PS10 – 20′YYYY?n/a
Alnus tenuifoliaaThinleaf alderHS/PS6 – 8′YYYYYApr
Amelanchier alnifoliaacSaskatoon alder-leaf serviceberryMS/PS6 – 8′YYYYYApr-May
Amelanchier utahensisaUtah serviceberryVL-MS4 – 6′YYNNNMay
Betula fontinalisaRiver birchHS/PS6 – 8′YYYY?n/a
Cercocarpus ledifoliusaMountain mahoganyVL-LS6 – 15′YY?NNn/a
Corylus cornutaaFilbert, beaked hazelnutHS/Sh5 – 6′YYY??n/a
Crataegus spp.aHawthorn (several native)MS6 – 8′YYYY?May
Fraxinus pennsylvanciaGreen ashM-HS20 – 25′YYYY?n/a
Gleditsia triacanthosHoneylocustM-HS60 – 70′YYNNNMay
Malus sp.CrabappleMS10 – 15′YYYYNApr-May
Physocarpus opulifoliusaTall ninebarkMS/PS4 – 6′YYY?NMay
Populus tremuloidesaAspenMS8 – 25′YYYYYn/a
Prunus americanaaAmerican wild plumMS/PS4 – 6′YYYYNApr
Prunus cerasiferaFlowering plumMS/PS8 – 10′YYY?NApr
Prunus pennsylvanicaaPin/fire/wild/red cherryMS/PS6 – 8′YYY?NMay
Prunus virginiana melanocarpaacWestern chokecherryM-HS/PS6 – 8′YYYYYApr-May
Rubus deliciosusaBoulder raspberry, thimbleberryMS/Sh4 – 6′YYYYYApr-May
Salix amygdaloidesaPeachleaf willowHS/PS20 – 30′YYYY?n/a
Shepherdia argenteaaSilver buffaloberryMS/PS4 – 6′YYYY?Apr
Sorbus scopulinaaWestern mountain ashM-HS/Sh6 – 8′YYYY?May
Syringa vulgarisCommon lilacMS6 – 8′YYYYYMay
a Native species.
b Ground cover plant.
c This species, or some species in this genus, may be poisonous to livestock, pets, wildlife and/or people under some conditions. Before planting, check with Colorado State University Extension, Colorado State Forest Service, or other knowledgeable personnel.
d Several speices of symphoricarpos are native.

* Staff Forester (retired), Colorado State Forest Service. 10/99. Revised 1/12.

Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating. CSU Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.

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