Written by Clare Booth-Downs, Herbarium Curator, Royal Horticultural Society Herbarium.

Moving On Up, To Move On Out

The Royal Horticultural Society Herbarium (RHS), which holds approximately 150,000 specimens and associated ancillary collections, had outgrown its original storage space.  The building of a new dedicated science and collections centre, RHS Hilltop, which opened in late June 2021, provided a solution to this. Hilltop, the home of gardening science, includes a larger, purpose built facility, the 1851 Royal Commission Herbarium.

Increasing the capacity of the herbarium was vital as the collection is expected to expand at a fast pace over the next few years.  With a full time plant collector now in place, the RHS’ ultimate aim is to hold a specimen of every species and cultivar of garden plant growing in the U.K. It is estimated this will be a collection numbering 400,000 specimens by 2050.

This repository will act as a reference point for gardeners, breeders, students and researchers as well as for ‘non-traditional’ herbarium visitors, for example, artists and designers looking for inspiration for fabrics and jewellery.  This is alongside one of the Society’s own research foci, as described by Professor Alistair Griffiths, RHS Director of Science & Collections, “In the UK, we’ve got a massive diversity of cultivated plants, originating from around the world, and all have potential for nature-based solutions.  We’re going to work towards a database of the garden plants and their uses from an environmental, and health and wellbeing perspective”.

Botanists and researchers will use the collection to look at the characteristics of the plants and their ability to deliver solutions to problems such as pollution capture or noise reduction. To facilitate this, the collection needed to be accessible and well protected and here lies the second, and some would argue more important reason for the move – to have a collection in the optimum conditions to ensure its longevity. 

The original RHS herbarium, located in the Laboratory building at Wisley, did not allow for expansion or gold standard integrated pest management techniques (IPM) to be used. The Biscuit beetles (Stegobium paniceum L.) had been a frequent visitor over the years, causing repeated damage to some of the specimens not treated with the more hazardous pest treatments of the past.

Meticulous Planning Pays Dividends

During the planning for the new herbarium, the IPM had been a central tenet of the specification requirements. Even down to choices of furniture and floor coverings, for example the desks being a smooth white surface (making pests more noticeable) and the chairs to be fully mesh so as not to harbour detritus, which could be a food source for the beetles. 

A further consideration was how the staff would use the herbarium suite of rooms.  As mentioned above, an ambitious programme of specimen collecting would begin once the herbarium was in its new location. New plant material being added to the collection would come in to the first room, the ‘dirty room’ which is the farthest from the herbarium store. Here the specimens would be prepared and described, including colour charting them at the north facing window. It was specified in the planning that the herbarium should be on the north side of the building for this reason.

Another feature of the suite is a room with a large window into the public atrium space so that visitors can see the volunteers demonstrating the mounting of herbarium specimens. The suite also has a room with a drying cabinet where the flower presses sit as they dry out, as well as a freezer to handle incoming herbarium material to ensure it is pest free.  Finally, at the far end of the corridor were the ‘clean rooms’, the Digitising office and herbarium store itself. 

Each room had individual temperature controls. The environmental controls within the herbarium stores were particularly important, as this would provide the optimum storage conditions required.  A particular feature are the walls, that are lined with a special Cornish clay covering which absorbs and releases moisture to passively maintain a steady humidity.

There are fire prevention blinds and a grid in the floor from which a fire suppressant gas is released when needed. The temperature and humidity of the herbarium are controllable, set at 15° and 50% humidity and regularly monitored.

Large metal compactors house the collection in blue archival storage boxes, which are covered in a water resistant material. These compactors are visible through a second large window that looks out into the Hilltop atrium and means that, for the first time, the herbarium team can show the public their work. Deep window ledges inside the herbarium store allow for small displays to be set out which can be quickly changed to reflect talks being given in the auditorium or a current horticultural hot topic.

A Year at Hilltop, the Pros and Cons.

Whilst moving an entire collection, as well as staff and their office equipment, at the height of the pandemic was an interesting challenge, it was an opportunity to work together on a once in a generation move.

There was certainly a sense of camaraderie within the teams.  Light-hearted competition over who could pack the most archival boxes helped to give a shared sense of purpose at a time when it would have been easy to succumb to the general gloom of the world beyond the herbarium.

The original plan to take the collection offsite for thermal pest treatment was thwarted by the second lockdown, which meant a new solution to the problem had to be sought. The delivery of a 10m freezer truck to Wisley meant nothing had to leave the site – a blessing for those of us who are custodians of the collection. The freezer truck worked perfectly, the collection was split into two parts and frozen for two weeks. This long freeze time was chosen to mitigate for a potential temperature of only -24°C, however the team were able to check at regular intervals and were delighted to note a consistent reading of -30°C.  This ensured a pest free collection moved up to Hilltop.

A year on, the Pheromone lures, blunder traps and building management system records confirm that the freezing treatment and environmental controls are working well. There have been no signs of infestations since the move.

The increased space within the suite has provided an additional benefit, we could recruit a team of tremendous volunteers, generously supported by the National Lottery Heritage Fund. Five collecting volunteers; Priti, Liz, Kaj, Michelle and Karen go out into the RHS gardens to collect new taxa which are not already held in the collection. 

Once pressed and dried the material passes to our second set of volunteers, the specimen preparers; Roya, Anna, Vivienne, Irina, Julia, Robert, Margaret, Tracey, Veronica and Lik-Kee who carefully prepare beautiful, representative specimens of the plants which will be digitised and databased before being added to the herbarium. Since joining us in autumn 2021, this dedicated team have helped to create over 1100 new specimens for the collection, a tremendous feat unachievable without their support.

The windows looking into the suite, known colloquially as the WOW (windows of wonderment) have increased our public engagement and more opportunities to raise the profile of RHS Science and the importance of cultivated plants.

And so to the ‘cons’, well I am afraid there aren’t any, unless you count the distraction of the Hilltop building being surrounded by beautiful gardens, but then again this is just additional source materials for specimen collecting.