The PCA will be taking invasive plants to the RHS Chelsea Flower Show to drive an important message to visitors. They’re showcasing 14 of the good, the bad and the ugly invasive non-native plants, which are currently thriving in gardens across the country. Entitled the “The Enemy Within - Managing Invasive Plants”, the showcase can be found within the Discovery Zone in the Great Pavilion at the RHS Chelsea Flower Show.
Professor Max Wade, chair of the PCA’s Invasive Weed Control Group, said: “Despite having more than 100,000 different plants available to gardeners in the UK, there is still a thirst for novel species.
“… giant rhubarb was first seen outside of gardens in 1908 and it wasn’t until about the turn of the century that it became invasive, while Japanese knotweed took from 1886 to around 1940 to start its ascendancy.
“Based on this, we should consider that not only is tomorrow’s Japanese knotweed growing in gardens today, but we are busy planting the follow-on generation to perpetuate the process.
“The PCA’s Invasive Weed Control Group (IWCG) is the front line in combating invasive weeds in the UK and Ireland and recognises that prevention is a whole lot better than the large-scale effort needed to keep Giant hogweed, giant rhubarb and Japanese knotweed invasions under control.
“Part of the challenge is to spot those species that have the makings of a problem for future generations.”
Steve Hodgson, chief executive of the PCA, says: “We don’t have to allow invasive plants to become such a big problem if we act responsibly. Non-natives which find niches in habitats, tend to grow without competition.
“If we are responsible about how we manage what we’ve got, we should be able to avoid the problems we see with things like Himalayan balsam, Giant hogweed and Japanese knotweed.”
Plants on show include the following:
Buddleia (Butterfly Bush)
B. davidii is a multi-stemmed shrub or small-tree that is native to China and has been introduced as an ornamental world-wide, first to Europe (1890s) and then later to the Americas, Australia, New Zealand, and some parts of Africa. Since that time, B. davidii has naturalised within sub-oceanic climates in the temperate and sub-Mediterranean zones.
The full potential of this species has yet to be realised; however, it is already considered problematic (i.e. out-competing native, agricultural, and forestry species) in northwestern and northeastern USA and Canada, throughout New Zealand, and in central Europe. B. davidii is tolerant of a broad range of environmental conditions, capable of prolific seed production, grows rapidly, and has a short juvenile period.
Crocosmia x crocosmifoliawas was originally created in France from parent plants of South African origin and is easily recognisable when in flower by the distinct shape and colour of their flower heads.
Introduced to the UK in 1880 as a garden plant. It escaped by 1911 both naturally and through the disposal of garden waste, and spread rapidly across the UK in the latter part of the 20th century. Can completely dominate habitat where it grows, sometimes excluding native plant species. Spreads mainly by rhizomes, rarely by seed.
Montbretia is listed under Schedule 9 to the Wildlife and Countryside Act 1981 with respect to England and Wales. As such, it is an offence to plant or otherwise allow this species to grow in the wild.
False Virginia Creeper
Parthenocissus inserta is a deciduous perennial woody climber, native to North America, that grows prolifically to 15m or more. It climbs by means of small branched twining tendrils which may have swollen ends but lack the cup-like adhesive pads of the very similar-looking Virginia-creeper P. quinquefolia. It has stalked five-lobed leaves with toothed edges which turn crimson before falling in the autumn.
It is native to north America and was introduced to the UK as an ornamental climber before 1824 and first recorded in the wild in 1948. It is often confused with Virginia-creeper, which shares its vivid red autumn foliage and the ability to screen unsightly areas.
A mature plant will scale most trees and shrubs. This causes several problems; the climber prevents the host and other plants below from receiving sufficient light and may cause death. Additionally, the weight of the climber can contribute to branch breakage or canopy collapse and finally it can girdle trees, effectively slowly strangling them over an extended period.
Lupinus polyphyllus is a herbaceous tuft-forming perennial, with unbranched stems with alternate, pamate leaves with long petioles. It's native to western parts of north America with an oceanic climate and was introduced to England in 1826. It can outcompete native species occurring in road verges, ruderal areas, gravelly floodplains and other habitats. Due to its nitrogen-fixing nodules, L. polyphyllus changes the soil chemistry and the consequent changes in community structure and diversity is the main problem when it invades and area.