This week we lift the lid on the RHS Herbarium, a unique collection of dried plant material from around the world that's used by scientists, researchers and artists. We learn how and why samples are prepared for inclusion – and share the recent discovery of a very special part of the collection: a potato that was brought back from the voyage of HMS Beagle by Charles Darwin.

Plus, plant pathologist Matthew Cromey shares tips with Guy Barter on how gardeners can avoid potato blight and Chris Young gets an insider's view on what visitors can expect at this year's RHS Flower Show Cardiff. For more info and useful links see www.rhs.org.uk/podcast