BBC Gardeners’ World Magazine Podcast · Immediate Media

Behind the scenes at RHS Wisley Herbarium, with Yvette Harvey

December 25, 2025·26 min·2 clips

Privet isn't just a hedge—it holds rainwater and filters pollution, according to recent research.

This episode features Claire Venice from BBC Gardeners' World Magazine in conversation with Yvette Harvey, the Keeper of the Herbarium at RHS Wisley. They explore the role of a herbarium as a scientific library of preserved plant specimens. Harvey explains the collection's purpose is to serve as a reference for plant identification, classification, and conservation. The herbarium is kept at 16°C and 50% humidity to minimize threats from insects like the biscuit beetle (*Stagobium paniceum*). Plant pressing methodology, invented in Italy in the mid-1500s, involves collecting plants in flower or fruit, documenting them with the RHS colour chart, and pressing them to show all plant aspects. Specimens are dried in a cabinet at 37°C, mounted on archival paper, and frozen to eliminate pests before digitization. The collection specializes in British ornamental cultivars and currently holds over 95,000 specimens, adding roughly 1,500 new ones each year. One notable specimen is a lavender collected from the Chelsea Physic Garden in 1731 by botanist John Martyn. The herbarium also holds a vegetable specimen collected by Charles Darwin during the voyage of the Beagle. A *Platycerium bifurcatum* (staghorn fern) from Wisley, studied by Professor Burns in New Zealand, is identified as the first recorded eusocial plant, where individuals have different roles for colony survival. Researchers at the University of Nottingham are training AI on the digitized collection to identify plants with traits for flood mitigation or pollution buffering. A surprising insight is that common privet (*Ligustrum ovalifolium*) is studied for its ability to hold rainwater and buffer airborne pollution. Harvey reveals that pressing plants at home can be done using cake-cooling racks, string, and heavy books, with baking parchment as a barrier against acidic newspaper. Drying times vary widely, with hyacinths and daffodils taking weeks while clematis can dry in days. Plant families and genera are arranged alphabetically, but reclassification, like rosemary moving into the *Salvia* genus, requires physically moving specimens across multiple racks. The digitization project, ongoing since 2011, safeguards the collection and makes specimens freely available online through RHS Digital Collections. Harvey also curates related archival materials, including 40,000 photographic slides and works of art that provide historical context for the specimens. The tone is conversational and educational, filled with personal anecdotes and detailed technical explanations. The style is warmly informative, focusing on the meticulous processes and hidden stories behind the collection. This episode would delight gardeners interested in botanical science, history, and detailed plant preservation techniques. Listeners seeking broad gardening tips or quick entertainment might find the specialized, process-oriented content less engaging.

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