Butterbur (Petasites hybridus) and winter heliotrope (P. fragrans) are herbaceous

Perennials are any plant living for at least three years. The term is also commonly used for herbaceous perennials which grow for many years (To compare: annual = one year, biennial = two years).

Rhizomes are creeping swollen root-like structures that are actually adapted stems. Roots, stems with leaves and flowers are produced along its length. See plants such as Anemone nemorosa, bamboo, canna, border iris.

rhizomes

The flowers of P. fragrans provide a valuable source of food for bees and other pollinating insects during the winter months. P. hybridus is also a good source of nectar for pollinators early in the year. 

Bees in your garden

Bees in your garden

This page looks at options for gardeners when Petasites are becoming a problem. 

Butterbur (P. hybridus) has clusters of unscented white flowers (tinged purple) on thick stems up to 40cm (16in) high, in early spring before the leaves. Mature heart-shaped leaves may reach 50cm-1m (20in-3¼ft) across on stalks to 1.5m (5ft) high, forming extensive colonies. This is a native plant, the male plant locally common throughout the British Isles and the female plant rare or absent from most areas except part of Northern England.

Winter heliotrope (P. fragrans) is conspicuous in winter with very pale mauve-pink, fragrant (vanilla-scented) flowers (November to March). A carpet of rounded leaves 20-30cm (8in-1ft) high appears with the flowers and persists until late autumn. Native to southern Europe but naturalized in Britain where only male plants are found.

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. 

Cultural control

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.

Weedkiller control

In borders

• 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 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
• 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.

Download

Weedkillers for gardeners  (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see sections 1a and 4)

Links

Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: using spot and broad-scale
Weeds: non-chemical control