Sensitive design and rigorous groundwork has helped breathe new life into the Grade II-listed Grosvenor Square
Grosvenor Square in Mayfair reopened in July this year following an ambitious £25 million redesign that transformed 193,750 square feet (18,000 sq m) of worn grass and limited planting into a climate-resilient urban woodland. When planning consent was achieved in 2021, design practice BDP took on an executive implementation role. ‘From the outset, we wanted to touch the earth gently,’ says Chris Stanton, BDP’s Landscape Architect Director. ‘We worked from the ground up to produce a climate-adapted icon that others can look to for future information and inspiration.’
Intensive site preperation
‘The soil was compacted and nutrient deficient [and] improving it was our first and most important action,’ Chris says. This was done using terraventing to loosen the soil within the 161,454-square-foot (15,000 sq m) planting site before enriching it by injecting a mixture of nutrients and biochar specified by soil specialist Tim O’Hare. ‘The probes were inserted by hand every half metre,’ says Chris. ‘Protecting the existing mature trees was a key priority.’ This hard-won decompaction was preserved during construction by using the final layout of paths for all works traffic. ‘We vacuum-excavated and 3D-mapped the root zones of several mature plane trees [in the places] where we were installing foundation screw piles for two new kiosk structures. I have never worked on a project which put so much resource into tree protection.’
Scheduling with plants in mind
When the garden square was laid out in 1725, it was envisaged as a ‘Wilderness Worke’, and this concept was reimagined for the 21st century by planting designer Professor Nigel Dunnett, who developed a diverse, drought-tolerant, woodland palette which would provide a biodiversity net gain of 15.5 per cent. ‘The construction schedule was calculated backwards from the best planting time, a risk because if construction was delayed, the plants would suffer,’ says Chris, ‘and almost everything was contract-grown for us in Britain, by Robin Tacchi Plants.’ A 5.9-inch (150mm) layer of enriched topsoil was added to allow for a no-dig approach to planting. ‘Planting was completed in torrential rain in April 2026. We always planned [to have] minimal irrigation, but the hosepipe ban [in London in 2026] meant we pulled back on watering even earlier than anticipated,’ Chris explains. ‘It’s a testament to the quality of the groundwork, and our contractors Maylim and Willerby Landscapes, that almost everything flourished despite the challenging summer.’
‘A giant urban sponge’
The original design brief specified attenuation tanks to contain stormwater run-off, but the design team was able to show that the re-worked ground could absorb up to 307,957 gallons (1,400,000 litres) of water. ‘This allowed us to make a case to Westminster City Council that a traditionally engineered system was unnecessary. We did add French drains in a few areas but essentially, the whole site is now a giant urban sponge,’ says Chris. ‘Instead of overloading the sewers, the ground takes care of it. And the plants benefit in the process. It was challenging to change the mindset, but we’ve delivered a new benchmark for sustainable drainage.’
bdp.com; grosvenorsquare.org; vimeo.com/1138117589
Words, Jodie Jones; photographs, Grosvenor
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