Japanese knotweed growing above Swansea rooftops and the bay

Abertawe · Invasive weeds

An independent eco-led guide to invasive weeds changing Swansea’s streets, riverbanks and wild places.

Invasive weeds.
Across Swansea.

Ecology before routine treatment. Survey first, contain spread and use the lightest effective method—including precise herbicide where genuinely needed.

01 / 04 · Swansea Bay

Japanese knotweed

Fallopia japonica

Our approach

Less force. More thought.

Observe

Identify the plant, season and habitat before disturbing it.

Contain

Prevent fragments, seed and contaminated soil from travelling.

Intervene lightly

Use digging, cutting or grazing where these methods genuinely fit.

Target precisely

Where herbicide is necessary, use the least needed in the right season.

Field index

Meet the beautiful troublemakers.

Look closely before you act. Similar leaves can demand very different responses.

Open the complete field guide

Highest risk

Japanese knotweed

Fallopia japonica

High risk

Himalayan balsam

Impatiens glandulifera

Highest risk

Giant hogweed

Heracleum mantegazzianum

High risk

Rhododendron ponticum

Moderate risk

Wall cotoneaster

Cotoneaster horizontalis and related species

Watch list

Montbretia

Crocosmia x crocosmiiflora

High risk

Running bamboo

Phyllostachys and related running species

Moderate risk

Buddleia (butterfly bush)

Buddleja davidii

Other weeds

The quiet spreaders.

All 14 in the guide

Garden escapes and hedgerow plants that spread more slowly — but still need watching, and still cannot be composted or dumped carelessly.

Moderate risk

Three-cornered leek

Allium triquetrum

Watch list

Japanese rose

Rosa rugosa

High risk

Cherry laurel

Prunus laurocerasus

Moderate risk

Himalayan honeysuckle

Leycesteria formosa

Aquatic weeds

Plants that live in the water.

Aquatic guide

Water carries fragments and seed further than any footpath. Never cut, dredge or compost these near a stream — call Natural Resources Wales on 0300 065 3000 first.

Moderate risk

American skunk cabbage

Lysichiton americanus

High risk

New Zealand pygmyweed

Crassula helmsii

Himalayan balsam flowering on a Welsh riverbank

Think like a river

Work upstream. Return next season.

Balsam seed and knotweed fragments travel through Swansea’s catchments. Good control follows the water, respects the habitat and plans beyond one visit.

Explore responsible treatment

Areas across Swansea and west Wales