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Arborvitae is not fire resistant; six assessments classify Thuja as highly flammable or advise against planting it in fire-risk settings.
The City of Ashland prohibits new planting or propagation within 30 feet of any structure, including structures on adjacent lots. Fire Safe Marin lists arborvitae among common fire-prone plants in Marin County. The University of Arizona Cooperative Extension also places it among fire-prone plants, which its bulletin says may ignite readily and burn intensely.
The Office national des forêts reached its very-high fire-sensitivity rating by combining bench measurements of inflammability, intensity, and combustion with foresters’ observations of fire damage. The Diputació de Girona and Catalonia’s fire service likewise advise against Thuja after considering fire research, fuel structure, maintenance, origin, invasiveness, and expert fire-service experience. Different methods and Mediterranean settings lead to the same practical warning.
The University of California Forest Products Laboratory found arborvitae not recommended by four earlier references for high-fire-risk areas. Its compilation cautions that many underlying lists used undefined terms or lacked a scientific basis, but the broader conclusion also rests on laboratory measurements, field observations, expert assessments, and a municipal restriction. Placement, spacing, irrigation, and removal of dead material remain necessary around any landscaping, yet they do not change Thuja’s classification. Near a home or other structure, arborvitae should be avoided.
City of Ashland (OR footprint); partial normalized coverage · 2026-08-26
This is a City of Ashland adoption fact, not statewide Oregon guidance or an experimental flammability result. FireApproved publishes 24 taxonomy-safe owners as city-level regulatory context. It applies to new planting and propagation within 30 feet of structures, including structures on adjacent lots; it is not projected as a blanket removal order for every established listed plant.
Marin County (CA footprint); partial normalized coverage · 2019-01-01
The publication is explicitly limited to plants common to Marin County. FireApproved publishes 104 exact owners as Marin regional context while retaining its placement, spacing, irrigation, and maintenance boundary. It is not statewide California guidance or parcel suitability.
The UC Forest Products Laboratory says the guide covers properties of common California landscaping plants and was prepared for California fire agencies. FireApproved publishes 130 exact owners at historical California publication scope. The report is a 1997 compilation, not a current endorsement, site rating, or independent test of every row.
Yavapai County (AZ footprint); partial normalized coverage · 2025-03-14
University of Arizona Cooperative Extension authors Bulletin 34 for Yavapai County. FireApproved publishes 198 exact source owners from its resistant and prone tables and keeps the county boundary visible. County publication scope is regional Arizona context, never statewide scope.
2. Why this plant is relevant here
State distribution
Documented in AZ.
Native range
Introduced / established
USDA hardiness
3. Legal, ecological, and broader status
Legal-list status
Seed-list status
Reported invasive here
Broader regional context
Federal context
How to read this page
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.
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.
Prohibited Flammable Plants: new planting or propagation restricted within 30 ft of any structure [Ashland Municipal Code setback] (with its avoid rating)
Guía de pirojardinería: not suitable inside the 25-metre maximum-risk zone [girona-2020-iuf-25m-suitability] (with its avoid rating)
Defensible Space Landscaping in the Urban/Wildland Interf…: Chapter 4, Landscape Vegetation Database [ucfpl-1997] (with its avoid rating)
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.
The fiche's overall sensitivity combines experimental-bench inflammability, intensity, and combustion measurements with foresters' observations of fire damage.
Thuja spp. is rated “DESACONSEJADA” by the guide's qualitative IUF garden-suitability method. The method assumes species-specific care and integrates fire evidence with fuel structure, maintenance, origin, invasiveness, and expert fire-service experience.
Listed as Arborvitae — Thuja sp.. The bulletin says fire-resistant plants tend to resist ignition when irrigated and maintained, while fire-prone plants may ignite readily and burn intensely.
