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The tall, pretty pink flower spikes of rosebay willowherb (Chamaenerion angustifolium) are a common sight on railway banks and disturbed woodland. It is a useful nectar source for pollinators but self-seeds readily making it a troublesome garden weed.
A native perennial weed which spreads by seed and rhizomes (underground stems) and is unsuitable in a small garden. It is found growing on waste land, scrub, rocks, woodland and also gardens where it can become a serious weed.
A white cultivar Chamaenerion angustifolium ‘Alba’ is available as a garden plant and shows less invasive tendencies than the pink form.
Height to 1.5m (5ft) with deep pinkish-purple flowers in tall spikes from June to September. When ripe the long seed capsules split open to reveal numerous fluffy seeds.
Rosebay willowherb is quick growing and produces abundant fluffy seeds which are readily carried on the wind. The roots are long, branched and spreading and give rise to new leafy shoots producing large weed patches.
Cultural methods such as hoeing and forking-out are effective against this shallow-rooted weed. Opaque mulching films can also be used to suppress its growth around woody plants or on unplanted beds.
Spot treat carefully with the non-selective weedkiller glyphosate (Roundup Fast Acting, Doff Glyphosate Weedkiller, SBM Job done General Purpose Weedkiller). Take care if applying such herbicides between ornamental plants by covering them with plastic sheeting whilst spraying. The covers can be removed once the spray has dried onto the weed foliage. Spraying with a ready-to-use formulation of glyphosate is probably the most accurate method of application.
In uncultivated land and around established trees and shrubs
SBM Job done Tough Weedkiller (ready-to-use only), SBM Job done Path Weedkiller (ready-to-use only) and Weedol Pathclear products containing glyphosate/diflufenican and can be applied once a season to natural surfaces where no plants are to be grown, and can also be applied under and around established woody trees and shrubs. This product kills off existing small green growth and prevents or checks developing growth. Check manufacturer’s recommendations before use to avoid damaging sensitive plants.
Inclusion of a weedkiller product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener.
Weedkillers for gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see sections 4 and 5)
Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: using spot and broad-scale
Weeds: non-chemical control
Brambles and other woody weeds
Butterbur and winter heliotrope
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The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.