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Showy forsythia's low flammability in whole-plant burns supports its fire-resistant listings.
Six assessments reach the same practical conclusion. Extension services in the Pacific Northwest, Tennessee, and Michigan list it among fire-resistant or Firewise plants. Ohio State and Virginia Tech each give it a low flammability rating, the recommended side of their respective scales. That agreement spans several regional planting guides rather than reflecting the judgment of one local source.
The strongest explanation comes from whole-plant burns conducted by the USDA Forest Service and NIST. Among 34 ornamental shrubs tested with large-scale calorimetry, showy forsythia fell into the low-flammability group. This matters because the finding came from burning whole shrubs, while the other sources rely mainly on expert judgment or inclusion in recommended plant lists.
Showy forsythia is a shrub in the olive family, suited to USDA zones 4a through 8b. Fire resistant does not mean fireproof, but both testing and regional guidance place this shrub on the safer side of the available choices. For a homeowner selecting vegetation with wildfire exposure in mind, showy forsythia has an unusually consistent case behind it.
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.
Michigan State University Extension Bulletin E2948 is explicitly a list of wildfire-resistant landscape plants for Michigan and includes a Michigan-native field. FireApproved publishes 221 exact GBIF owners from 226 represented source rows and holds 15 complex or non-exact rows. This dated publication scope is not a current site-suitability determination.
Ohio State University Extension Bulletin 921 is an Ohio publication that describes Ohio fire seasons and landscape conditions and labels nativity to Ohio. FireApproved publishes 352 exact source-owning plant records from its eight rated tables. This historical publication scope does not assert current extension endorsement or that a listed plant suits every Ohio site.
The October 2023 joint Pacific Northwest Extension publication explicitly names Oregon, Washington, and Idaho and publishes more than 150 plant profiles. FireApproved has normalized 155 exact plant records from the source; publication scope does not assert that every listed plant suits every site within the three states.
University of Tennessee Extension SP685 is Tennessee landscape guidance and publishes 78 represented plant owners. Most table rows are a carrier of Virginia Firescapes rather than an independent rating; Tennessee source scope does not change that lineage or establish site suitability.
Virginia Cooperative Extension's publication opens with Virginia wildfire conditions, identifies its Virginia Firewise Landscaping Task Force, and labels plants native to Virginia. FireApproved publishes 306 exact source owners. Publication scope does not establish parcel suitability or current endorsement of this archived 2009 list.
2. Why this plant is relevant here
State distribution
Documented in ID, OR, WA.
Native range
Introduced / established
1 sourced range or established record. This is not an invasive warning.
USDA hardiness
2 applicable cited hardiness statements overlap but have different boundaries; compare each complete source row.
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.
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.
4–8 explicit range · whole zone precision · source stated
Source taxon: Forsythia x intermedia · exact match.
Source location: Forsythia hybrids profile, USDA hardiness zones field.
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.
Eastern United States Fire Performance Plant Selector: Landscape Zone 2 — 5–10 ft from the structure; maintained lawn or fuel breaks, with easily ignited evergreens avoided [Fire Performance Plant Selector landscape zone] (mid-scale rating)
Fire Resistance of Plants Master Database: plantable at 50' from home [Idaho minimum planting distance] (mid-scale rating)
Guía de pirojardinería: suitable inside or outside the 25-metre maximum-risk zone [girona-2020-iuf-25m-suitability] (with its recommendation)
Fire-resistant plant profile galleries: Forsythia hybrids — Forsythia x intermedia [osu-2023-shrubs-gallery] (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.
Forsythia x intermedia is rated “RECOMENDADA” 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.
