Pretty monsters: Invasive plants that can become a nightmare - Gardening with Brendan

Research, research, research. I know from experience how important it is to learn about the plants you are growing or buying almost a decade on from digging out something I planted in the garden which spread all over. I’m still finding bits of it popping up in between paving cracks and at random spots.

Japanese anemone

I bought this at an indoor fair many moons ago. It was tiny, in a little pot with one white flower on it. It stayed in that pot for a few years indoors and behaved itself fine. Then I had the bright idea of putting it in the ground to see if would grow any. Big mistake. Within a couple of years it had choked out several other perennial plants in the same patch and just took over. And while the mass of white blooms in late summer was very eye-catching, it was also pretty clear that this big brute needed to go before he spread any further.

I didn’t know what the plant was when I bought it and only after doing a bit of research did I find out that it was a Japanese anemone. And an absolute pain to try and get rid of. It spreads through rhizomes- these complex root systems which colonise an area and create new plants nearby. It comes in white and pink and is beautiful and while far from the most harmful invasive plant in Ireland, it will spread rapidly and is there for the long haul so my advice would be to avoid it.

There are numerous other plants who are not native to here which have had a much bigger impact and which have thrived in Ireland’s damp, relatively mild climate such as Japanese knotweed, Himalayan balsam, Indian balsam, giant rhubarb, bamboo, giant Hogweed and one of the most virile and widespread, Rhododendron.

Rhododendron ponticum

This is another plant native to Asia and parts of southern Europe that has wreaked havoc in numerous areas across Ireland since it was first brought here for ornamental gardens around 300 years ago.

It has strangled out native woodland in some areas, taking root and spreading like wildfire also in towns, farmland, grassy areas and even rubbish tips. According to the Irish government, there are over 900 species of Rhododendron, but only Rhododendron ponticum is invasive in Ireland and it is described as being “particularly invasive in the west, north-west and south-west of the country”.

Japanese knotweed

you won’t find this for sale but you may come across it in the city and in rural areas. Do not pick it. It is extremely difficult to get rid of, spreads very easily and can be found along with warning signs along riverbanks and even in cities. It is strong enough to rip up through tarmac and concrete and millions of pounds has been spent over the years in trying to eradicate it in some areas.

Giant hogweed

This is most prevalent in the north of Ireland and it is the stuff of nightmares.

Not only can it grow as tall as a tree it is also dangerous to touch. So much so that back in 2020 one Derry City & Strabane District Councillor brought it to the attention of the local authority. Giant hogweed is an invasive species with skin burning sap which can result in permanent scarring or even blindness if it gets into your eyes. There have been instances of children and adults ending up with severe burns as a result of coming into contact with it.

The Northern Ireland government has issued this advice: “Giant hogweed is easily distinguishable from the similar native hogweed and cow parsley due to its sheer height which can reach three to five metres. It is most commonly found in areas of damp soils, such as river banks.”

What’s worse is each flower head can produce up to 50,000 seeds and those seeds can live for up to two decades.

Native plants and garden friends

Our eco system is very finely balanced and our wildlife, from the creepy crawlies below ground to the critters above it, the birds of the air to the fish in the sea have all adapted to the natural world and the native plant life here over millennia. It is their home as much as it is ours and we should do what we can to protect that habitat. Our few remaining forests, our coastal plains, our waterways are changing due to climate shifts so if we can to minimise the impact we have on the native species of plants and animal life around us that can help them weather the storm. And one way we can do that is by educating ourselves on how we can help.

There are so many native trees, shrubs, hedgerows, food crops and and non-invasive, wildlife-friendly flowering plants and shrubs that can provide food for pollinators and a haven for birds and other important little native garden visitors like hedgehogs and frogs.

Ireland is certainly not alone in having invasive species threaten native flora and fauna. Most countries in the world are dealing with similar issues and it is not always the big nasties. For instance the humble nasturtium is invasive in some parts of America’s coastline and the cottage garden favourite, the majestic lupin has become invasive in Iceland.

It is perhaps inevitable that in today’s globalised world invasive species will continue to make their way to our shores and from our shores, but with a little bit of knowledge we can all help limit its impact and protect our precious habitats.