Invasion of the Plot Snatchers

Various foreign plant species made headlines recently when a nation-wide governmental prohibition was imposed on their import and distribution in the UK. The ban, which boasts the support of the RHS, outlines five species in particular whose invasive nature, if allowed the opportunity, could threaten our native flora and over time, dramatically transform the appearance of the British ecosystem.

Though these varieties were previously controlled, in that their disposal had to be conducted in a controlled environment, the new legislation threatens any would-be importers or distributers of this species with a fine of £5000 and up to six months imprisonment.

Dr. John David, a senior scientist at the RHS, has this to say:

“Our gardens have been greatly enriched by the introduction of plants from abroad but a small number have proved highly invasive in the UK, threatening natural habitats and native species. This is particularly the case with aquatics as they are spread more quickly through our waterways, having a serious impact on our rivers and ponds, and are extremely difficult and costly to control. Although these plants are no longer widely available, this is a much-needed step to close off the supply of these problem plants.”

The five species, for the international importers among you, are as follows:

Water fern

Water fern (Azolla filiculoides)

Parrot’s feather

Parrot’s feather (Myriophyllum aquaticum)

Floating pennywort

Floating pennywort (Hydrocotyle ranunculoides)

Water primrose

Water primrose (Ludwigia grandiflora)

New Zealand pygmyweed

Australian swamp stonecrop or New Zealand pygmyweed (Crassula helmsii)

So be warned!

However, as it is springtime, it may also be prudent of us to reflect on some of the other invasive species that continue to threaten British flora, how to spot them and how to deal with their disposal.

Japanese Knotweed

Japanese Knotweed

Or as I affectionately refer to it “Satan’s hairnet” – a plant so destructive that its feats have almost become an urban legend, from destroying foundations to lifting concrete! It is a clump forming perennial plant that produces tall, reddish stems and small white and red flowers in the springtime – so you know what to look out for.

Giant Hogweed

Giant Hogweed

This is a perennial with red/purple stems and spotted leaf stalks, they also sport sturdy bristles later on in their blooming cycle. The overall appearance of the plant is one of snow cones in bunches, with wide spherical flower heads on elongated stems.

Fortunately, due to their notorious reputation, the proper treatment for invasions of these varieties is easily accessible and more importantly, encouraged by government bodies. It is recommended that you use a combination of different techniques in order to ensure their destruction. Though there are a variety of techniques available for this task it is generally recommended that you use a combination of them for greatest effect. The three basic techniques fall into through categories: spraying, digging and disposal.


Spraying entails treating any exposed, i.e. above ground, plant matter with chemical weed killer and, for the knotweed in particular, would recommend a solution rich in glyphosate and that you begin this process in May, repeating in mid-summer and early autumn. It may take several seasons to attain the desired effect, but consistency is crucial unless you want to pay professionals to do the job.


The second phase is centred around digging out and disrupting as much of the pre-existing growth as possible, as with any plant this slows its growth cycle and generally detriments its health, however, similarly to the chemical methods, with plants of such virulence it will be necessary to continue this habit for several seasons.


Finally, we have disposal, ideally the specimen should never leave the site upon which it is found to reduce risk of exposing further areas, so where possible burn all material pertaining to the plant. However, if you are unable to burn it, then you should be aware that invasive species fall under ‘controlled waste’ and must be disposed of at a licenced landfill and never with normal household waste.

By Josh Ellison

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