Triffids

Ardnamurchan has an unwanted squatter, an evergreen cancer spreading inexorably along the shores of Loch Sunart and – triffid-like – extending its tentacles up the steep, narrow valleys leading up onto the hills.

The invasion is particularly bad around Glenborrodale, the northern bulge of Morvern and the Salen area across the loch, Resipole, Ardery and – further North – Kinlochmoidart and the area to the east of Castle Tioram.

Forestry Commission rhododendron control areas

Forestry Commission rhododendron control areas

I am, of course, talking about rhododendron. More specifically – as there are many varieties of rhododendron – I’m talking about Rhododendron ponticum.

Rhododendron invasion

Rhododendron is not a native plant to the UK, at least not since the last ice age. Its natural range includes Spain and Portugal, Bulgaria, Turkey and a large swathe of central Asia (Himalayas, Afghanistan, Northern Pakistan, India and Kashmir). Genetic evidence indicates that the plants in the UK originated from the Iberian peninsula. 

The specific name, ponticum, refers to the Pontus area south of the Black Sea where it was first identified by the botanist Joseph Pitton de Tournefort at the beginning of the 18th Century. It was introduced to Britain in 1763 via Gibraltar as an ornamental shrub and was popular in Victorian country estates.

Glenborrodale Castle

Glenborrodale Castle

How and where it first appeared on Ardnamurchan is unclear. It is well established in the Glenborrodale area, particularly around the castle, so it may have been introduced when Glenborrodale Castle was built and the grounds landscaped (1898-1902). Its spread east along the loch would have then been aided by prevailing westerly winds.

What does rhododendron do?

Rhododendron is highly invasive and spreads widely by seeds and suckering, thriving in the damp conditions of Ardnamurchan as well as other areas of western Scotland, Wales and Ireland.

It forms evergreen spreading bushes 2-8m high that quickly outcompete other flora by casting dense shade under the long, dark green, glossy leaves. In Spring it bears lilac, light or dark purple flowers that can appear very dramatic when it covers entire hillsides.

But don’t be seduced by this brief spectacle. Where rhododendron is out of control – as it is on Ardnamurchan – it has dramatic and damaging effects on habitat structure and native biodiversity.

This includes eliminating native plants that are unable to compete for light and the consequent loss of native animals.

The CABI Invasive Species Compendium states that “where R. ponticum is introduced in an area all plant species are threatened”.

One thing rhododendron does not do is ‘poison the soil’ as is often reported. There is no good evidence that rhododendron is allelopathic. James Merryweather has written a comprehensive article on why this piece of folklore probably became established.

Rhododendron has no natural predators. The leaves, flowers and nectar are toxic due to the presence of diterpines, known as grayanotoxins. Therefore the foliage is unpalatable to herbivores and insects. Honey produced from rhododendron flowers contains grayanotoxins and is known as ‘mad honey’. I’ve recently written about mad honey, the mechanism of toxicity and the symptoms in humans on my beekeeping website, The Apiarist.

Rhododendron control

We’ve got a lot of well-established rhododendron on our land. The evergreen leaves provide a sort of semi-attractive, year-round verdant appearance to the site. However, I can’t ignore the damage they’re doing to the flora and fauna.

One day all this will be under rhododendron

One day all this will be under rhododendron

The bushes above are not yet encroaching on the view of Loch Sunart. However, they’re ‘only’ about 3-4m tall at the moment. They will get bigger.

They have to go.

I’m going to write separately on how to control rhododendron once I’ve worked out a reliable way that works best for me. Essentially methods are either manual or chemical, or the double-whammy of both.

Manual methods include mechanical flailing with a modified tractor, so-called ‘Lever and Mulch’ or simply cutting them down with a machete or chainsaw. Chemical methods usually involve glyphosate or similar weedkillers.

The disadvantage of manual methods is that the roots will reshoot unless they are killed or removed. The disadvantage of many chemical methods is that it involves widespread use of rather indiscriminate weedkillers. The local flora is struggling already … I don’t want to make it worse.

I currently favour the ‘drill and drop’ combination of tightly focused topical application of glyphosate, followed by the tightly focused application of my Trusty Husky chainsaw 😉

Or, of course, ‘drop and drill’ which is exactly the same in reverse.

The Day of the Triffids

Triffids are a fictitious tall, mobile, prolific and highly venomous plant species from John Wyndham’s 1951 novel The Day of the Triffids. Of course, rhododendron are not triffids …

The Day of the Triffids movie poster

The Day of the Triffids movie poster

… or are they.

Rhododendron are tall, they’re mobile 1, they’re highly prolific 2 and – although they’re not venomous – they are toxic.

So perhaps the name is appropriate.

I’ve already described how they damage local flora and fauna, but are they a threat to humans?

Well, probably not, though there are several recent cases where tourists or hill walkers have become trapped in dense rhododendron ‘forest’ in the Republic of Ireland.

I’m off to do battle with this lot … if you hear shouting call the emergency services 😉

Rhododendron jungle

Rhododendron jungle


Notes

A brief but thorough account of the damage that rhododendron do to the environment can be found here.

The Day of the Triffids is the 1951 post-apocalyptic science-fiction novel by John Wyndham, a pseudonym of John Wyndham Parkes Lucas Beynon Harris (1903-1969). The novel was made into a film of the same name in 1962. The story is well known, involving a blinding meteor shower, the eponymous carnivorous plants, survivalist groups, the Isle of White and – of interest to a beekeeper – the disablement of an armoured car by pouring honey into the fuel tank.

  1. in that they spread widely.
  2. a single plant can generate millions of seeds and, through suckering, it’s not unusual for a single plant to cover 100m2.

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