Firewise Plant Materials | Colorado State University Extension Website

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.

Introduction

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's attractive colors — Opuntia is exceptionally hardy and can provide attractive colors and textures in your landscape. (Photo by I. Shonle)

Rocky Mountain Penstemon plants next to yellow wall — Rocky Mountain Penstemon is a hardy, native plant with value for both landowners and beneficial insects (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. 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 for more information on these mitigation measures.

Low/High Falammability Score meter chart — Choose plants with higher scores to lower fire risk

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.

Suggested Plants

Key

Water Needs:
VL = Very Low; L = Low; M = Medium; H = High

Sun / Shade Requirements:
S = Sun; PS = Part Sun; Sh = Shade; Prt Sh = Part Shade

Table 1. Native, low-water flowers and ground covers

Scientific Name	Common Name	Approx. Water Needs	Sun/Shade Preference	Approx. Mature Height	Flower Color	Elevation (1,000’/k)	Approx. Bloom Time	Low Flammability Rating
Achillea lanulosa, now A. millefolium	common yarrow	L-H	S/PS	1.5–2′	white	5–10K	Jul	9.5
Allium cernuum	nodding onion	L-H	S/PS	1′	pink/purple	5–10K	Jun 10	10
Allium geyeri	Geyer’s onion	L-H	S/PS	1′	pink	5–10K	Jun 10	10
Antennaria parvifolia	small-leaf pussytoes	M	S/PS	<5″	creamy white	5–10K	Jun	8
Antennaria rosea	rosy pussytoes	M	S/PS	<5″	rose	5–10K	Jun	8
Aquilegia chrysantha	golden columbine	M-H	S/PS	1–2′	yellow	5–10K	Jun–Aug	8
Asclepias tuberosa	common butterfly weed	L-M	S	1–2′	orange	5–6K	Summer	8
Symphyotrichum (f. Aster) laeve	smooth aster	L-H	S/PS	1–3′	blue/lavender	5–10K	Aug–Sep	8
Symphyotrichum (f. Aster) porteri	porter aster	L-M	S	1′	white	5–10K	Aug–Sep	8
Astragalus utahensis	Utah milkvetch	L	S	0.5′	pink/purple	5–6K	Spring	8
Callirhoe involucrata	poppy mallow	L	S	5″	pink/white	5–8K	Summer	8
Calochortus gunnisonii	Gunnison’s mariposa lily	M-H	S	1.5–2′	white	5–10K	Jul–Aug	8
Campanula rotundifolia	harebell, bluebells of Scotland	M-H	S	5–1′	blue	5–10K	May–Oct	9.5
Claytonia lanceolata	western spring beauty	M	Sh	1.5–1.5′	white	5–10K	Mar–Apr	9.5
Coreopsis tinctoria	plains coreopsis	L-M	S	2.5–3′	yellow	5–10K	Summer	8
Erysimum capitatum	western wallflower	M	S/PS	1+’	yellow	5–10K	Jun–Jul	9
Gaillardia aristata	blanketflower	L-M	S	1–1.5′	yellow-reddish	5–10K	Jul–Sep	8
Galium boreale	northern bedstraw	M-H	Sh	<1′	white	5–10K	May–Jun	8
Geranium caespitosum	Rocky Mountain geranium	M	Sh/PS	2′	pink/purple/white	5–10K	May–Oct	8
Geum triflorum	prairie smoke	M	S/PS	1.5′	reddish pink	5–10K	Jun	8
Leucocrinum montanum	sand lily	L-M	S	<1′	white	5–8K	May	10
Linum lewisii	Lewis or blue flax	L	S	2.5′	blue	5–8K	Late Spring–Early Summer	8
Lupinus argenteus	silvery lupine	M	Sh/PS	1–3′	blue	5–10K	Jun–Jul	8
Mertensia lanceolata	prairie bluebell	M	Sh/PS	1–2′	blue	5–10K	May–Jun	10

Oenothera speciosa	evening primrose	L-M	S	<1.5′	white-pink	4–7K	May–Jul	8
Penstemon caespitosus	mat penstemon	L-M	S	<.5′	purple	5–10K	Jun 8	8
Penstemon secundiflorus	sidebells penstemon	L-M	S	1–2′	blue/violet/pink	5–9K	May–Jun	8
Penstemon teucrioides	germander beardtongue	L-M	S	.5′	purple/violet	5–10K	Jun	8
Penstemon spp.	penstemon species, cultivars	L-M	S	1–2.5′	blue/purple/violet	5–9K	Summer	8
Penstemon strictus	Rocky Mountain penstemon	L-M	S	2–2.5′	purple/violet	5–10K	Jul	8
Penstemon virens	Front Range beardtongue	M	S/PS	.5′	blue	5–10K	Jun	8
Sedum lanceolatum	yellow stonecrop	M	S/PS	.5′	yellow	5–10K	Jul–Aug	10
Thermopsis rhombifolia var. divaricarpa	spreadfruit golden banner	M-H	S/PS	2′	yellow	5–10K	May	8

Table 2. Native, low-water shrubs, trees, and cacti

Scientific Name	Common Name	Approx. Water Needs	Sun/Shade Preference	Approx. Mature Height	Flower Color	Elevation (1,000’/K)	Approx. Bloom Time	Low Flammability Rating
Amelanchier alnifolia v. utahensis	Utah serviceberry	VL-M	S	4–6′	white	5–7K	May	7.5
Cylindropuntia spp.	cholla	VL-M	S	3–5′	pink	5–6K	Jun 8	8
Opuntia spp.	prickly pear	VL	S	5–7′	yellow/pink	5–7.5K	May	10
Philadelphus lewisii	Cheyenne mock orange	M	S	2–3′	white	5–9K	Jun	8
Populus tremuloides	aspen	M	S	8–25′	catkins	5–10K	n/a	8
Rhus glabra	smooth sumac	L	S	3–5′	yellow	5–8K	Apr 8	8
Rhus trilobata ‘Autumn Amber’	Autumn Amber sumac	L	S/PS	1′	yellow	5–7.5K	Apr 8	8
Symphoricarpos albus	snowberry	M	S/PS	2–3′	white/pink	5–9K	n/a	8
Yucca baccata	banana yucca	VL-L	S/PS	2–3′	white	5–6K	Jun	8
Yucca glauca	soapweed, Great Plains yucca	VL-L	S/PS	2–3′	white	5–7K	Jun 8	8

Table 3. Non-native, low-water flowers and ground covers

Scientific Name	Common Name	Approx. Water Needs	Sun/Shade Preference	Approx. Mature Height	Flower Color	Elevation (1,000’/K)	Approx. Bloom Time	Low Flammability Rating
Aegopodium podagraria ‘Variegatum’	variegated bishop’s weed, goutweed	M	S/PS	8″	white	5–8K	not showy	8
Ajuga reptans	bugleweed	H	Sh	<.5′	blue	5–10K	Jun–Jul	8
Alchemilla mollis	Lady’s mantle	M-H	PS/Sh	1′	yellow	5–9K	Jun–Jul	8
Arabis spp.	rockcress	L-H	S	<1′	white	5–10K	May–Jun	8
Armeria maritima	sea thrift	L-H	S/PS	.5′	white	5–10K	Apr–Jun	8
Aubrieta spp.	false rockcress	M	S	1′	pink/white/purple	5–9K	Apr–May	8
Aurinia saxatilis	basket of gold	M	S/PS	1′	yellow	5–9K	Apr–May	8

Bergenia cordifolia	heartleaf bergenia, pigsqueak	M	PS/Sh	1′	pink/purple	5–9K	Spring	8
Centranthus ruber	Jupiter’s beard	L-H	S/Sh	2–2.5′	red	5–10K	May–Aug	10
Cerastium alpinum v. lanthanum	alpine mouse-ear	M	S/PS	1′	white	5–10K	May–Jun	8
Cerastium tomentosum	snow-in-summer	L-M	S/PS	1′	white	5–9K	May–Jun	8
Ceratostigma plumbaginoides	plumbago	L	S/Sh	.5′	blue	5–6K	Fall	8
Convallaria majalis	lily-of-the-valley	H	Sh	<1′	white	5–9K	May–Jun	8
Coreopsis spp.	tickseed, coreopsis	M	S	1.5–2′	yellow	5–8K	Summer	8
Delosperma nubigenum	hardy yellow ice plant	M-H	S	.5′	chartreuse-yellow	5–8K	Jun	10
Delosperma spp.	ice plant	L	S	1.5–2′	yellow	varies	Spring	10
Dianthus spp.	pink	L-H	S	<.5–2′	pink	5–10K	May–Aug	9
Diascia integerrima ‘Coral Canyon’	Coral Canyon twinspur	M	S/Prt Sh	1–1.5′	rose-pink	4–7K	Summer	9
Doronicum spp.	leopard’s bane	H	S/PS	2–3′	yellow	5–9K	Jul–Aug	10
Echeveria spp.	hens-n-chicks	L	S/Prt Sh	1–2′	varies	5–9K	Summer	8
Ephedra regeliana	Regel’s jointfir	L	S	6–12″	yellow	5–12K	Spring	8
Erysimum linifolium	wallflower	L	S	1–3′	varies	4.5–12K	Spring–Summer	9
Euonymus fortunei	winter creeper	M	S/Prt Sh	3′	green-white	4.5–8K	Spring	8
Euphorbia polychroma	cushion spurge	L	S	12–18″	yellow	5–8K	Spring	10
Euphorbia x martini ‘Mini Martini’	Martini’s spurge	L-H	S	1.5–2′	chartreuse	4–6K	Late Spring	10
Fragaria spp.	wild strawberries	M	S/Prt Sh	.25–.75′	white	5–11K	Summer	9
Geranium spp.	hardy geraniums	M	Sh/PS	2′	blue/pink/purple/white	5–10K	May–Oct	8
Helianthemum nummularium	rockrose, sunrose	M-H	S	<1′	pink	5–8K	May–Jun	8
Hemerocallis spp.	daylilies	L-M	S/PS	1–3′	yellow/red/orange	5–7.5K	Summer	10
Iberis sempervirens ‘Little Gem’	Little Gem evergreen	M	S	.5–1′	white	4.5–9K	Spring	8
Iris germanica	bearded iris	L-M	S	1–3′	numerous colors	5–10K	May–Jun	8
Kniphofia uvaria	red hot poker	L	S	3′	red/yellow	5–6K	Summer	8
Lamium spp.	spotted deadnettle	M-H	Sh	<1′	white/purple/pink	5–10K	May–Jun	8
Lilium spp.	lilies	M	S/PS/Sh	1–8′	varies	4–6.5K	Summer	10
Lupinus spp.	lupine	L-M	S/PS	2–3′	lavender/blue	5–10K	Summer	8
Marrubium rotundifolium	silver-edged horehound	VL-L	S	1.5–2.5′	white	5–6K	Summer	8

Muscari armeniacum	grape hyacinth	M	S/PS	6–9″	blue	4.5–10K	Spring	10
Nierembergia gracilis ‘Starry Eyes’	‘Starry Eyes’ cupflower	M	S	10″	purple (lt. lav.)	4.5–5.5K	Summer/Late Summer	8
Nierembergia repens	creeping white cup	M-H	S/PS	2–4″	white	4.5–5.5K	Jul–Sep	8
Oenothera berlandieri	Berlandier’s sundrop	L-M	S	1′	yellow	4.5–6.5K	Early Summer–Fall	8
Pachysandra terminalis ‘Green Sheen’	Green Sheen pachysandra	M-H	Sh	6–8″	white	4–8K	April–May	8
Papaver orientale	Oriental poppy	H	S/Sh	2–3′	orange/pink/red	5–10K	May–Jun	8
Polemonium spp.	Jacob’s ladder	M	S/PS	1–2′	blue/white	5–10K	May–Aug	8
Polygonatum commutatum	great Solomon’s seal	M-H	PS/Sh	2′	white	4–10K	May–Jun	8
Salvia officinalis	common or garden sage	L-M	S/PS	2′	blue-lavender/pink/lavender	5–8K	Jun	7.5
Saxifraga hirsuta	saxifrage	H	S/PS	5+’	white	5–10K	May–Jun	8
Scutellaria alpina ‘Moonbeam’	alpine skullcap	M	S/PS	5–1′	white/purple	4–8K	May	8
Sedum spp.	stonecrop	M	S/PS	1–1.5′	yellow	5–10K	Jul–Aug	10
Sempervivum spp.	hens and chicks, houseleeks	L-M	S/PS	.5′	pink	5–10K	n/a	10
Solidago sphacelata ‘Golden Fleece’	Golden Fleece goldenrod	VL-M	S	1–1.5′	yellow	4–8K	Aug–Sep	8
Thymus serpyllum ‘Minus’	Elfin thyme	L	S	1–3″	pink	4–10K	Early–Late Summer	8
Trifolium spp.	clover	M	S/PS	1–2′	white/purple/pink	varies/spp.	varies: May–Oct	8
Veronica pectinata	woolly creeping speedwell	L-M	S	<.5′	blue	5–9K	Apr–Jul	8
Vinca minor	common periwinkle	H	Sh	<1′	white	5–10K	Apr–Jun	8
Waldsteinia spp.	barren strawberry	M-H	Sh/PS	<1′	yellow	5–9K	May–Jun	8

Table 4. Non-native, low-water trees and shrubs

Scientific Name	Common Name	Approx. Water Needs	Sun/Shade Preference	Approx. Mature Height	Flower Color	Elevation (1,000’/k)	Approx. Bloom Time	Low Flammability Rating
Berberis thunbergii ‘Atropurpurea Nana’	crimson pygmy Japanese barberry	M	S	2–3′	yellow	5–7.5K	Spring	8
Ceanothus americanus	New Jersey tea	M	S	2–3′	white	5–7.5K	Summer	8
Lonicera tatarica	Tatarian honeysuckle	M	S	4–6′	white/pink	5–10K	May–Jun	8
Malus spp.	crabapple	M	S	10–25′	white/pink/red	4.5–8K	Apr–May	8
Yucca filamentosa	Adam’s needle	M	S/PS	2–3′	white	5–8K	Summer	8

Table 5. Turf grasses

Scientific Name	Common Name	Approx. Water Needs	Sun/Shade Preference	Approx. Mature Height	Flower Color	Elevation (1,000’/K)	Approx. Bloom Time	Low Flammability Rating
Bouteloua dactyloides	buffalograss	L	S	mow to 2″	n/a	5–6.5K	n/a	9
Bouteloua gracilis	blue grama	L	S	mow to 2″	n/a	4.5–7.5K	n/a	9
Festuca ovina	sheep fescue	M	S	mow to 2″	n/a	5–9K	n/a	9
Lolium perenne	perennial ryegrass	M	S	mow to 2″	n/a	5–8K	n/a	10
Poa compressa	Canada bluegrass	M	S	mow to 2″	n/a	5–8K	n/a	9
Poa pratensis	Kentucky bluegrass	M	S	mow to 2″	n/a	5–9K	n/a	10

Table 6. Low-flammability Plants with Higher Water Needs

Scientific Name	Common Name	Approx. Water Needs	Sun/Shade Preference	Approx. Mature Height	Flower Color	Elevation (1,000’/k)	Approx. Bloom Time	Low Flammability Rating
Aconitum columbianum	Columbian monkshood	M-H	S	2′	blue/purple	5–10K	Jun–Jul	7.5
Aconitum spp.	monkshood	M-H	S	2′	blue/purple	5–10K	Jun–Jul	7.5
Aquilegia caerulea	Colorado blue columbine	M-H	S/PS	1–2′	blue-lavender/white	5–10K	Jun–Jul	8
Aquilegia spp.	columbine	M-H	S/PS	1–2′	varies	5–10K	Jun–Jul	8
Corylus cornuta	beaked hazelnut	H	S/Sh	5–6′	yellow-brown	5–7.5K	inconspicuous	8
Hosta spp.	hosta	M-H	PS	2–3′	varies	varies	Summer–Fall	8
Iris missouriensis	Missouri or native iris	M-H	S	1–2′	violet blue	5–10K	May	9.5

Additional Resources

Home Ignition Zone Guide, 2021 | Colorado State Forest Service (1)(4)

Low-Flammability Landscape Plants | Colorado State Forest Service (2)(4)

Fire-Resistant Landscapes – Plant Materials | Idaho Firewise (3)(4)(5)

Notes on Additional Resources
(1) The CSFS Home Ignition Zone (HIZ) guide describes the concepts of structural ignitability and defensible space. (2) Low-Flammability Landscape Plants recommends fire-resistant plants for zones 1 and 2 identified in the defensible space section of the CSFS HIZ guide. (3) Fire-Resistant Landscaping recommends design features for zones 1, 2 and 3 and recommends plants with mitigation measure for plants and existing vegetation in zone 3. (4) 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. (5) The Idaho materials provided the basis for the addition of the flammability scoring and approach for this update.