Cultivated hybrid: Wilkinson Eyre’s Home of Gardening Science

Hilltop, Home of Gardening Science, Wilkinson Eyre’s £35 million new building at the Royal Horticultural Society (RHS)’s gardens at Wisley in Surrey, poses a question about the language of architecture. You may know the site, as I did, from seeing the signs for it while driving out of London on the A3. It started life as a place of science with laboratories and trial fields. Now it is better known by its 1.2 million annual visitors (pre-Covid) as a garden-based visitor attraction, with cafés and shelves of plants to buy. The institution’s mission is split and so too is the building.

Set on the site of old glasshouses and the Honest Sausage café, Hilltop attempts to house café, flower shows and functions with plant science labs, library and classrooms in a bifurcating Y-shaped plan. On the science side it takes over from the Edwardian laboratories with their fluctuating temperatures, floods and biscuit beetles, which didn’t sit well with ensuring bio-secure labs or storing specimens from Charles Darwin’s Voyage of the Beagle. And it spreads out the visitors, giving them another destination, away from the existing honeypots of cafés, loos and shop at the entrance and the great glasshouses. 

The two functions and the two other garden destinations set the diagram of the building. Wilkinson Eyre’s Jim Eyre throws open his arms to demonstrate the welcoming embrace of the plan, one arm out towards the entrance, the other to the glass houses.

What is the right language for a building that takes in all these functions? Should it have the presence of a great house, like the old labs, or the massing of a village cluster like the more recent welcome buildings? Should it have an arts and crafts flavour like the small cottages dotted around? None of these. Away from other buildings, Hilltop crests the hill, taking over from a broad belt of trees and half hidden by more trees from the main garden. Its narrow lengths of sweet chestnut cladding signal its fit with this wooded edge. In some places they hint at an agricultural antecedent. But the 2m cladding modules that the chestnut sits within tell another story, of buildability over craft. As does the ground floor in-situ concrete which took over from the lower-carbon steel option amid concerns for the programme when the contractor, Osborne, came on board. Large steels, glass expanses, an atrium; this large scale way of building – and designing for that – has dogged university and school building of the last 15 years; lofty ambitions with feet of concrete. 

Climbing up to Hilltop, the building reaches out towards you with that embrace but it is the gable ends that, oddly, are the first encounter, as if those arms are not thrown quite wide enough. And the building appears as if in many angled pieces. Each side of the ‘Y’, and the central atrium volume, has a split section with a clerestory for ventilation. Add in a glazed colonnade on each side and then extend two sections of glazed atrium roof as canopies over the colonnades and you don’t know where to look. 

The last few Wilkinson Eyre buildings I  visited were for James Dyson on his campus in Wiltshire, which stand taut with design discipline. Hilltop has none of that rigorous editing of materials and expression. This is emphasised by its immediate surroundings where early planting has yet to take hold and soften the edges of the paths, and the scale of the plants throws the architecture into coarse relief.

Inside, the design is more straightforward. The rigour of the steel grid marks out the atrium which sweepingly connects formal gardens at the front with the informality of the green beyond the building – although this is currently stymied by the exhibition design and its large-scale panel at the entrance. The atrium neatly both draws together and divides the separate functions. One arm of the building has ‘science’ with a herbarium of rolling shelves of horticultural specimens, and a more conventional library of books. Above are plain labs where work on pests and diseases can be investigated in a contained way. The offices – unusually – bring the building to life as they stretch out towards the glazed gable ends with coloured baffles suspended from the thin 50mm concrete planks of the soffit (giving the space thermal mass). 

The second wing has classrooms opening out on to garden teaching spaces and the newly planted world food garden. A small café kinks out from the atrium as the wing opens out into a double-height event hall with rooflights and windows sliced into the facade. They are part shaded, with hit-and-miss cedar slats above double doors. The building is contained – and partially protected from the noise of the A3 – by a bund edging the ‘back’ of the building and bursting with poppies and grasses. 

The last decade has seen a huge investment in buildings and gardens by the RHS, both at its new Bridgewater Garden in Salford and at Wisley. At times there have been 30 capital investment projects running. At Hilltop’s opening, ‘ambition’ was a big theme, along with new Covid recruits to gardening and the potential positive impact of 30 million gardeners and their pots and plots on climate change and the biodiversity crisis. 

What is surprising is that this ambition and climate concern didn’t translate into a more fundamentally sustainable building. Yes, it has timber cladding, PVs, LEDs and water attenuation. But it doesn’t, to give the most obvious example for a horticultural charity, use plants to improve air quality nor to create a protective microclimate around the building. Instead there are a few climbers scrambling up wires on the west elevation and a sample panel of a planted living wall inside. Experimenting with this could have put the RHS in the lead on another important area of garden science and put the £9 million investment in gardens at Hilltop to a double use. And perhaps it could have found a more appropriate expression for the fascinating work going on in this hybrid building. 

In numbers
£35m Total contract cost, building and garden
£26m Cost of building
£4,905 GIFA cost per m² 
5,300m² Total area