Don’t spare the rhododendrons
11 July, 2013
Last week I was visiting Mavisbank House and gardens in Midlothian. I have mentioned Mavisbank in this blog before. It was built between 1723 and 1736, designed by Robert Adam for Sir John Clerk of Penicuik.
The house is located on the north bank of the North Esk valley. Loanhead lies immediately to the north-east, and the property stretches eastwards to Lasswade. I was there to look at the rhododendron which grow around the house in within the woodland. Rhododendrons are not native to Scotland. The first species was introduced from Switzerland in the late 1600s. Rhododendron ponticum, the species seen in woodlands throughout Scotland, was introduced from Gibraltar in 1763.
The popularity of rhododendrons took off in the late 1860s, when there was an outbreak of ‘rhododendromania’, as it has been called. This was largely due to the heroic efforts of an well-travelled English plant hunter, Sir Joseph Dalton Hooker.
A close friend of Charles Darwin, Hooker spent three exhausting years in the late 1840s in northern India, where he gathered many exotic colourful rhododendrons.
Building a collection of rhododendrons became an obsession with many wealthy landed gardeners and the designed landscape of many Scottish estates changed dramatically as a result. Most of the introduced rhododendrons were quite fragile, so they were often grafted onto ponticum rootstock. If not managed, the plants would revert back to the ponticum – this is one of the reasons why rhododendron ponticum is so widespread throughout Scottish woodlands.
Unfortunately rhododendron has become a problem in woodlands as it forms a very dense canopy which prevents other plants growing. It also exudes a chemical which suppresses other plant growth. This leads to a serious decrease in the biodiversity of woodlands.
In addition, rhododendrons are liable to infection by ‘sudden oak death’, a fungus-like organism which affects many species of woody plants. For these reasons it has become increasingly important for landowners to eradicate this problem species. Incidentally there are reported cases of poisoning from eating ‘honey’ made from rhododendron, which is toxic to humans.
It’s not just the biodiversity that suffers. Rhododendron also completely obscures what is within the landscape. Behind Mavisbank House there is evidence that the steep slope was landscaped. At the base of the slope there is evidence of two paths cut into either side of the slope. It is hoped that removing the rhododendron will reveal the evidence of what was once a formal garden.
On the subject of biodiversity, I finish by mentioning the BioBlitz at Castle Campbell this weekend, 13 and 14 July 2013. Organised by the National Trust of Scotland and Historic Scotland, the BioBlitz is your chance to work alongside experts to monitor and survey the local wildlife, plants, birds and insects. Guided walks will be run throughout both days, and there will be a bat walk on Saturday evening. Check the events page on the Historic Scotland website for details.