Is fiery beauty Montbretia an invasive species?

Montbretia is a common sight in Kerry and provides a great splash of colour to roadsides and boundaries in summer and autumn. Montbretia is easily recognised when in flower by it’s distinct shape and bright colour of its flower heads.

The trumpet-shaped flowers are orange-red with yellow centres and form in two rows along a tall stem. The flowers form fruit capsules that turn from green to brown and become shrivelled as they mature in autumn. During winter months dead brown leaves, stems and seed heads can be seen as remnants of the flowering plant.

It may come as a surprise to many that Montbretia is regarded an invasive perennial plant. It is a horticultural hybrid which was developed in France for ornamental purposes in the 1880s. Since then, it has escaped into the wild and spread rapidly across Europe during the latter part of the last century.

It has naturalised in many parts of Ireland including Kerry. Montbretia can invade most low-growing habitats such as wet grasslands, gardens, hedgerows, pastures, waste areas and roadsides once the plant has the damp conditions it prefers.

Concern about Montbretia derives from fact that biodiversity of ecosystems can be significantly affected by an infestation of the plant. Once it becomes established, Montbretia out-competes local flora and forms large dense stands which will be familiar to anyone who has seen the plant in Kerry. Montbretia displaces native vegetation by smothering ground cover plants, small shrubs and retarding indigenous seedlings. Montbretia is hardy and is capable of colonising a variety of habitats. Small fragments of roots can easily separate from the parent plant and become established in the wild.

Plant growth begins in early spring with leaves sprouting vigorously in March.

The grass-like leaves are bright green, flat and sword-shaped. The leaves are soft, hairless and have pointed tips and grow up to 80cm in length. Flowering takes place between July and September.

Montbretia’s primary mode of spreading is through underground corms and rhizome fragments. Farmers and gardeners will be familiar with the corm - which is something similar to a bulb. Each Montbretia plant can produce up to 14 new corms or bulbs annually. These break off from the parent plant and begin to produce their own root network. This in turn increases the size and density of the Montbretia growth area. Montbretia bulbs or corms can be spread unintentionally as a result of ground disturbance and dumping of garden waste in areas that the plant can take a foothold.

Complete eradication of Montbretia from a site may take a number of years. Either non-chemical treatment, chemical treatment or a combination of both can be employed to remove the plant. As Montbretia is capable of regeneration from corms and small fragments of roots, all plant material must be handled and disposed of in a way which does not result in further spread of the plant. The most effective time to remove Montbretia is just before full flowering occurs in summer. Control of Montbretia is something of a medium term project as eradication will require continued follow-up over a number of years to deal with re-growth by corms and rhizomes.