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The Rhododendron - Friend or Foe?

The Rhododendron is a very popular genus of shrubs, especially as many have large colourful flowers in spring after an often long winter.  They are generally evergreen (except the deciduous Azaleas - a lovely fragrant one with yellow flowers is Rhododendron luteum - grows to 4m) but they tend to only grow well in acidic soils.  If they look as if they are poorly (yellowing leaves often due to lack of nutrition) then you can feed them special plant food obtained from garden centres.

The first known cultivated Rhododendron species was Rhododendron hirsutum, which was found growing in the Alps in the sixteenth century, and was cultivated in the century following by John Tradescent (the younger). 

However, the most widely grown Rhododendron species in the past has been Rhododendron ponticum which was discovered by the Black Sea at the beginning of the eighteenth century.  It was brought to England in 1763 by plant collectors and was widely grown as an indoor container plant by 1803. As it became more popular it began to be used as a landscaping shrub.   Unfortunately, this plant has proved to be very invasive. In Britain and Ireland the main problem is that each mature rhododendron shrub can produce up to a million seeds.  These are distributed by the wind (especially if the shrubs are on hillsides or other prominent positions) and the species will naturalise on heaths, in wooded areas and even on lightly-grazed grasslands. It is known to reduce populations of nesting birds, is poisonous to livestock and is not eaten by many insects. 

It can carry an infection called Phytophora ramorum too which infects native species of trees etc. It grows in shade and in full sun, but it grows so tall and so thick that other plant species cannot grow underneath it. This is especially a problem in a woodland ecosystem which relies on light being available to different species occupying different tiers. It may be responsible for the local extinction of bluebells and is now listed in the Wildlife & Countryside Act as a plant which should be prevented from spreading to the wild.  EG in Snowdonia National Park, it has now spread to over 2,000 ha.  The total cost to eradicate it from the area was estimated to be £10 million in 2008, and attempts to control it have been ongoing since the 1930s. 

What we can do about the problem

Volunteer!  The National Trust and other bodies such as the British Trust for Conservation Volunteers and Wildlife Trusts often conduct task days in winter to remove Rhodedendron ponticum….. this a very nice occupation for a chilly winter’s day when you want to be outside but also want to keep warm!  I can recommend it!

Plant other species of Rhododendron in your garden.  Less invasive cultivars can be found in garden centres and nurseries - they have the added advantage of often only growing to a maximum height of 1m or 1.5m which means they are more suitable for smaller gardens.  Take care to add ericaceous soil to the planting hole when planting though!!

Learn more about horticulture with an ACS horticulture course. We cover a variety of different subject areas from Azaleas and Rhododendron's, to Garden Design, principles of horticulture and much more. Our selection of courses cater for different levels of knowledge - from beginners to advanced and specialists. Our Horticulture courses have been extensively developed over decades,and are written and taught by myself and other expert tutors. A selection of our courses and links to Horticulture courses directory csn be found at the bottom of this page.

All of our courses are studied by distance learning and can be started at anytime. Many of our courses include practical elements and exercises so that you can test and apply your knowledge as you learn.

If you have any questions or want to know more, please get in touch today.

Article by -

Diana Cole, Horticulture and Permaculture Tutor

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