Butterbur and winter heliotrope

Butterbur and winter heliotrope (Petasites spp.) form large carpets of leaves in damp, shady areas. Winter heliotrope can be a useful ground cover in wild gardens but becomes a weed in borders.

Winter heliotrope Petasites fragrans

Quick facts

Common and botanical names Butterbur (Petasites hybridus) and winter heliotrope (P. fragrans)
Area affected Damp meadows and woodland, stream banks and borders
Main causes Spread by rhizomes and root fragments
Timing Carpets of leaves from spring to autumn; treat from summer to autumn

What is butterbur and winter heliotrope?

Butterbur (Petasites hybridus) and winter heliotrope (P. fragrans) are herbaceous perennials occurring commonly throughout much of the Britain, in damp meadows, river banks and woodlands. They spread by rhizomes (underground stems) which can regenerate from tiny fragments.

Appearance

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) conspicuous in winter with dull 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 problem

Petasites spread by rhizomes (underground stems) producing large carpets of leaves crowding out other plants. Winter heliotrope with its fragrant flowers is useful where shade-tolerant groundcover is needed in a “wild garden” but is too vigorous for the border.

Control

Non chemical

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.

Vigilance is needed to remove any seedlings as they appear.

Chemical

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. Scotts Roundup Ultra, Bayer Garden Rootkill Weedkiller, Bayer Garden Super Strength Weedkiller or Doff Maxi Strength Glyphosate 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 (Scotts 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

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

Advertise here

Gardeners' calendar

Advice from the RHS

Find out what to do this month with our gardeners' calendar

Advice from the RHS

Did you find the advice you needed?

RHS members can get exclusive individual advice from the RHS Gardening Advice team.

Join the RHS now

Discuss this

for the site or to share your experiences on this topic and seek advice from our community of gardeners.