it’s true. Alien invaders are taking over and
threatening much of our wildlife. Certain pond weeds,
which are readily sold and recommended in garden centres
and in gardening magazines, are jumping the garden fence
and escaping into our wild ponds and waterways causing
widespread ecological havoc.
Water features have become very popular recently and
it’s certainly true that a pond in your garden
can be hugely beneficial for wildlife. But if you put
certain alien oxygenators into your pond, and even worse,
if you unwittingly throw your surplus plants into local
waterways, you could be helping these invaders on their
We all know about Japanese Knotweed and Giant Hogweed,
longtime successful havoc makers. Well now we’re
talking New Zealand Pigmyweed, Parrot’s Feather
and Floating Pennywort, to name the worst offenders
(otherwise known as Crassula helmsii, Myriophyllum aquaticum,
and Hydrocotyle ranunculoides).
New Zealand pigmyweed has invaded many SSSI (site of
special scientific interest) areas and is threatening
the existence of one of our rarest plants, the starfruit.
Parrot’s Feather can grow at a rate of 15cm a
day and can completely choke up waterways if left unchecked.
Floating Pennywort can form dense floating mats that
can grow 10cm a day. These mats have already clogged
drainage channels leading to flooding.
All of these bullies can grow into new colonies from
tiny fragments of stems. It’s obviously very easy
for these plants to be transferred from the confines
of a garden pond to the greater outdoors, not only by
humans but also by animals and birds. Some are even
used in aquarium tanks and can contaminate waterways
through the drainage system.
Eradication of these plants is very difficult, often
impossible and always expensive. Herbicides are costly
and ruthless to all wildlife, not just the invading
culprits. The cost of treating every contaminated natural
habitat site is estimated at £4 to £5 million per year.
So what is the answer
for the discerning gardener? Well, if you care about
our native flora and fauna, the only answer is to avoid
In fact the organisation Plantlife is trying
to get the sale of them in this country banned completely.
They’re recommending that the government includes
them on the schedule 9 list which is part of the Wildlife
and Countryside Act which makes it an offence, without
a licence, to plant or cause to grow in the wild any
plant on the list.
Currently, a species can be placed on schedule 9 only
if the plant is already established in habitats in Great
Britain and has been shown to cause damage to the natural
environment. Having said that, even if these aquatic
invaders get put onto the list, it will have relatively
little effect as long as the plants are still widely
So really it does rely on the consumer to make a real
difference. My advice for this month is to steer well
clear of these aquatic invaders and buy native plants
instead. Certainly if you’re trying to attract
native wildlife, you can’t go wrong. Native oxygenators
such as spiked water-milfoil, curly pondweed and starwort
along with floating plants such as frogbit and waterlilies
are just a few to recommend.
A thought to leave you with is this quote from Plantlife:
‘invasive species are likely to be the biggest
threat facing our biodiversity this century’.
It’s something that all caring gardeners need
to be aware of.
Stay gardening wild.
For more information about Plantlife and their activities
telephone 020 7808 0100.
Illustrations: Natural Image
reprinted with premission from Greenfingers.com