The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.
Where Petasites is growing amongst plants, e.g. herbaceous perennials, carefully lift valuable plants and free them of the weed before replanting.
Winter heliotrope (Petasites fragrans) cannot stand efficient cultivation so thorough and repeated digging, rotovating or deep hoeing will eliminate it. Improving drainage will also reduce the weed’s vigour.
Where cultivation is not possible consider covering the affected areas with a weed membrane or thick, light-excluding bark mulch for at least 6 months.
Repeated strimming or mowing will eliminate the weed from empty ground.
- Apply glyphosate as a spot treatment to individual plants or spray areas that have been cleared of cultivated plants
- Glyphosate is a non-selective weedkiller applied to the foliage, where it is translocated throughout the weed. Tougher formulations are worth trying (e.g. Roundup Ultra, SBM Job done General Purpose Weedkiller, SBM Job done Tough Weedkiller (soluble sachet only) or Doff Weedout Extra Tough Weedkiller)
- Being non-selective it is essential to avoid spray drift onto neighbouring plants. It is important to have good leaf coverage so that as much chemical is absorbed as possible
- Protect cultivated plants with sheet polythene or by pegging them out of the way, and take care to avoid spray drift. The gel formulation (Roundup Gel) may be easier to apply in such a situation
- Sprays are most effective if applied mid-summer or later when the plants are growing strongly. There may be re-growth the following spring necessitating further treatment
- Used with care, glyphosate is safe to use around the base of non-suckering woody plants, as long as the bark is woody, brown and mature. Glyphosate is not active through the soil and there is therefore no risk garden plants will absorb it through their roots
In rough grassland
Apply a selective weedkiller which contains triclopyr (SBK Brushwood Killer) as this would leave the grass unharmed. This herbicide is systemic, travelling from the weed foliage down into the root system
However as it is non-selective any broad-leaved plants will be damaged (e.g. wild flowers) and so should only be used in grass where such action is acceptable.
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 1a and 4)
Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: using spot and broad-scale
Weeds: non-chemical control