United States / Grow / Japanese knotweed

Japanese knotweed (Polygonum japonicum (Fallopia japonica))
Photo: (c) 黃美滿, some rights reserved (CC BY) (CC BY), via iNaturalist. Species-typical, not necessarily this cultivar.

Japanese knotweed

Polygonum japonicum (Fallopia japonica) (accepted: Reynoutria japonica) · Polygonaceae · all Polygonum records · syn. Fallopia japonica, Polygonum cuspidatum · Wikipedia

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Is this one for your yard?

Enter your ZIP to see whether this is legal to plant in your state, and whether it survives your winter.

Polygonum binds keep away recommendation. On polygonum japonicum fallopia japonica, limited evidence is the next polygonum japonicum fallopia japonica fact. The citations do not collapse — Polygonum. avoid does not replace limited evidence on polygonum japonicum fallopia japonica.

On polygonum japonicum fallopia japonica, Polygonum also carries Combustion characteristics of north-eastern for polygonum japonicum fallopia japonica. On polygonum japonicum fallopia japonica, Polygonum also carries legal list for polygonum japonicum fallopia japonica. On polygonum japonicum fallopia japonica, Polygonum also carries cured test condition for polygonum japonicum fallopia japonica.

Use evidence on polygonum japonicum fallopia japonica for polygonum japonicum fallopia japonica. The citations remain on Polygonum for polygonum japonicum fallopia japonica.

Fire-resistant shrubs instead

Form
shrub
Mature height
~8 ft
Light
Full sun
Rated in
Global; eastern US; north-eastern and mid-Atlantic United States
On this lot

1. Fire evidence and conditions

Fire evidence
Highly flammable — location does not change the cited classification.
Fire-performance conditions
1 condition stated in cited fire-evidence rows.
Placement evidence
1 source placement record; source schemes remain separate.
Evidence regions
Global; eastern US; north-eastern and mid-Atlantic United States
Typed publication scope: 1 scope across 1 cited fire source
  • Combustion characteristics of north-eastern USA vegetation tested in the cone calorimeter · Official scoped edition
    • Northeastern and mid-Atlantic study sites (ME, MD, MA, NY, VA footprint); partial normalized coverage · 2007-08-20

      The authors collected foliage and twigs across study sites in Maine, Maryland, Massachusetts, New York, and Virginia, then conditioned and tested the samples in a cone calorimeter. FireApproved publishes 37 exact source owners only as multi-state laboratory context. The source does not establish that every taxon was sampled in every named state, whole-plant behavior, landscape suitability, or state planting guidance.

2. Why this plant is relevant here

State distribution
Documented in AK, AR, CA, CO, CT, DC, DE, GA, IA, ID, IL, IN, KS, KY, LA, MA, MD, ME, MI, MN, MO, MS, MT, NC, NE, NH, NJ, NY, OH, OK, OR, PA, RI, SC, SD, TN, UT, VA, VT, WA, WI, WV.
USDA hardiness
Only uncertain or inapplicable hardiness rows are cited; no primary zone is projected.

3. Legal, ecological, and broader status

Legal-list status
3 legal-list records; the Place chip matches exact scope.
Plant-specific legal-list reviews (1)

These source-bound review receipts are separate from ecological invasive reports. A source or plant identity change invalidates a receipt.

Plant-specific state seed-list reviews (1)

These source-bound receipts answer only the July 2026 state noxious-weed seed-list question.

This answers only whether the plant identity appears in the July 2026 state noxious-weed seed sheet. It does not establish non-seed plant legal status, ecological-invasive status, nursery-sale rules, or unrestricted use.

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.

Conditions in the fire evidence

These describe tested or rated plant material. They are not horticultural maintenance instructions.

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.

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.

Avoids (1)

Mid-scale / conditional (1)

Listed without a rating (1)
Corroboration (1 rows from 1 source)
  • FLAMITS: FLAMmability plant traiTS database — Dryad / Global Ecology and Biogeography · Dryad version 9 · original source Corroboration Trait database lineage: meta-aggregator

    “calorific value (kcal/kg): 2866.15”

    FLAMITS record 2882; Combustibility measurement; plant part leaves; fuel live; predrying yes; device calorimeter; site Dibble2007-1; sampling ND. Primary study Dibble2007: Dibble, A. C., White, R. H., & Lebow, P. K. (2007). Combustion characteristics of north-eastern USA vegetation tested in the cone calorimeter: invasive versus non-invasive plants. International journal of wildland fire, 16, 426-443.

Fire-resistant shrubs instead

Fire-resistant shrubs listed above

Last verified 2026-08-23. JSON (CC BY 4.0)

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Polygonum japonicum (Fallopia japonica) (Japanese knotweed). FireApproved. https://fireapproved.com/plants/polygonum-japonicum-fallopia-japonica/. Last verified 2026-08-23.