Enter your ZIP to see whether this is legal to plant in your state, and whether it survives your winter.
Prairie thermopsis is rated fire resistant, supported by favorable scores and regional planting recommendations.
Idaho Firewise records an eight-out-of-ten fire-resistance score for Thermopsis divaricarpa. Colorado's extension and forest service table prints an eight under Thermopsis rhombifolia variety divaricarpa, named spreadfruit golden banner. Eight qualifies under Colorado's rule for defensible-space Zones 1 and 2. That rule belongs to Colorado, whose guidance credits Idaho material for the scoring basis.
Oregon State University Extension profiles this perennial as spreading golden banner among fire-resistant plants suited to the Willamette Valley. Fremont County also lists Thermopsis divaricarpa among its Firewise ground covers. These are additional favorable landscape recommendations, with the Oregon growing-region scope attached.
The practical answer for prairie thermopsis is therefore favorable. A gardener has a published score that meets Colorado's selection criterion and regional listings that point in the same direction. The repeated eight should retain its source relationship, while the differing scientific-name forms remain attached to the publications using them.
Form
perennial
Rated in
Colorado / Rocky Mountain Front Range; Fremont County, Wyoming; Oregon (Willamette Valley); southern Idaho / Intermountain
On this lot
1. Fire evidence and conditions
Fire evidence
Fire-resistant — location does not change the cited classification.
Colorado State University Extension and the Colorado State Forest Service publish Fact Sheet 6.305 for Colorado's WUI and varied ecosystems. FireApproved exposes all 114 exact source owners at Colorado publication scope while retaining score, elevation, water, and Idaho-carrier lineage. Publication scope is not suitability for every Colorado site or zone.
Fremont County (WY footprint); partial normalized coverage · 2011-02-25
The source identifies itself as the Fremont County Firewise Plant List. FireApproved publishes its 92 exact source owners as Fremont County regional context. No methodology, current county endorsement, statewide Wyoming scope, or site-specific suitability is inferred.
Southern Idaho (ID footprint); partial normalized coverage · 2013-11-08
The official database labels itself "For Southern Idaho" and describes Idaho residents at the urban-rangeland interface. FireApproved publishes 419 existing plant owners that cite its scored rows. This bounded Southern Idaho scope is regional context, not statewide coverage or a conclusion that the score transfers unchanged to every Idaho site.
Willamette Valley (OR footprint); partial normalized coverage · 2015-02-01
OSU Extension says EM 9103 highlights fire-resistant plants that thrive under Willamette Valley growing conditions. FireApproved publishes 172 exact owners only as valley context. The guide shares the PNW 590 lineage and is not a second independent vote or statewide site clearance.
The status above is computed from the cited rows below: independent recommendations can support a fire-resistant result, an avoid row can produce keep-away, and disagreement stays visible as conflict. Placement notes preserve each source’s own scheme rather than translating unlike rules into one scale. This is evidence about a plant, not permission to plant it in every part of the defensible space; Zone 0 remains noncombustible.
Plant hardiness evidence
These values describe the plant source. Your ZIP zone comes from the separate 2023 USDA
Plant Hardiness Zone Map. Whole-zone values stay whole-zone, and a single unresolved value
is not treated as a tolerance range. Different source boundaries stay separate: overlapping
statements are compared independently, while only ranges with no shared zone are called a conflict.
Source location: Spreading Golden Banner profile (PDF page 92).
Where its sources say to plant it
Placement rules below use each source's own distances or named zones, tied to its rating.
They are not interchangeable with the directory's current Zone 0 guidance.
Fire Resistance of Plants Master Database: plantable at 30' from home [Idaho minimum planting distance] (with its recommendation)
Fire-resistant Landscape Plants for the Willamette Valley: Spreading Golden Banner profile (PDF page 92) [osu-em-9103-profile] (with its recommendation)
Ignition-Resistant Landscape Plants: suitable for defensible-space zones 1-2 (score 8+) [CSU defensible-space zone] (with its recommendation)
The evidence
Grouped by what each source concluded. Primary evidence rated the plant itself
(a lab, field program, or original curation); corroboration compiled or
republished another source's rating and resolves to its root lineage.
“fire-resistant plants that thrive in Willamette Valley growing conditions”
The perennials profile lists Thermopsis divaricarpa as Spreading Golden Banner. The profile prints USDA Hardiness Zone: 4–8.
Ignition-Resistant Landscape Plants (Fact Sheet 6.305) — Colorado State University Extension / Colorado State Forest Service (Wildfire Mitigation Series) · 2025 · original sourcePrimary evidenceField programlineage: idaho-tree resolves to Fire Resistance of Plants Master Database
“ignitability score 8 of 10”
· score 8 (idaho-0-10)
CSU 6.305 table lists Thermopsis rhombifolia var. divaricarpa (spreadfruit golden banner) with the preserved ignitability score.
“Fremont County Firewise Plant List — Thermopsis divaricarpa — Spreading Golden Banner”
Listed in the source's Ground Covers section; the page describes its listed Firewise plants as generally low-growing, low-debris, and relatively moist.
