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Head gardener Charlie Harpur describes the approach as a form of ‘curation’ gently steering the plantings but otherwise allowing them to find their own way.
A historic garden in Southern England aims to radically boost its biodiversity in an experiment that pushes at the boundaries of what counts as ‘gardening’. What does ‘rewilding’ mean in a horticultural context? And what lessons might this project have for producers and consumers? Martin Deasy investigates for FloraCulture International.
Knepp estate near Brighton introduced the concept of ‘rewilding’ to Britain a quarter century ago, inspired by the experimental reserve at Oostvaardersplassen in the Netherlands.
Realising that their 1,400-hectare estate could no longer be farmed economically, Charlie Burrell and Isabella Tree decided in 1999 to abandon intensive agriculture, delegating ‘management’ of the estate to wild cattle, pigs, and ponies brought in to graze it.
With minimal human intervention, the resumption of natural processes has fostered an astonishing diversity of flora and fauna. Controversial at times, Knepp’s experiment has proved both profitable and influential, sparking a keen interest in the potential of ‘rewilding’ as an environmentally responsible, ethical approach to land stewardship.
Ferula communis, the giant fennel, is a species of flowering plant in the carrot family Apiaceae.
Rewilding at a smaller scale
However, not everyone is privileged to manage an estate on the same scale as Knepp (the average size of an English private garden is just 188 m2). So in 2019, its owners set out to discover what could happen if similar principles were applied at a more domestic scale, allowing natural processes to unfold within a medium-sized garden with only light-touch management from gardeners.
The project involved the transformation of Knepp’s 0.6 ha Victorian walled garden from a neatly managed, ecologically homogeneous site into a resilient, sustainable and species-rich environment that remained, nevertheless, an attractive garden—full of interest and variety.
Clematis adds to the general atmosphere of field flowers.
Ups and downs
Diversity of habitat is the key to a properly functioning and diverse ecosystem, so the first step in Knepp’s scheme was to break up the homogeneity of the site in order to create a mosaic of habitats.
Working to plans by designer Tom Stuart Smith, advised by horticultural ecologist James Hitchmough and plant ecologist Mick Crawley, areas of the pancake-flat croquet lawn were excavated to create depressions and mounds of site-recovered crushed concrete.
This reconfigured topography—elevations now varying by up to 3m across the site—created marked differences in aspect, drainage, soil type and fertility, diverse conditions favouring a variety of different plant communities. A carefully designed matrix of herbaceous perennials (many bare root) was planted, and the area was oversown with bespoke perennial seed mixes for shade and open conditions.
The walled garden on Knepp Estate.
Diversity depends on disturbance
Allowing natural processes to drive the garden’s development isn’t just a case of letting nature take its course, however—that would only result in thickets of bramble and buddleia.
Instead, Knepp’s gardeners model their approach on larger-scale rewilding schemes. Research demonstrates that the reason why natural landscapes look the way they do—that is, their physical structure or ‘physiognomy’—is overwhelmingly due to the influence of large herbivores (and, in turn, the predators that control them).
These ‘keystone species’ have a marked effect on the landscape through the disturbance they introduce—grazing, browsing and ground foraging. Pigs rooting for bulbs and tubers create tilth in which new seedlings can germinate, while deer selectively graze and crop vegetation, keeping vigorous young plants in check. The habits, tastes and behaviours of these keystone species are what maintain an ecosystem in its characteristic balanced, lasting state.
Timeline of Knepp’s rewilding project
The land at Knepp is not conducive to modern intensive farming. Three hundred twenty metres of heavy Low Weald clay over a bedrock of limestone, the soil is like concrete in summer and unfathomable porridge in winter. For seventeen years after taking over the 3,500-acre Estate from his grandparents in 1983, Charlie Burrell did his utmost to make Knepp Home Farm profitable, but it was impossible to compete with larger, industrialised farms on better soils.
In February 2000, the decision was made to sell the dairy herds and farm machinery and put the arable out to contract – clearing the Estate’s mountainous debts.
A moment of epiphany came in 2001 when Knepp received Countryside Stewardship funding to restore the Repton Park in the middle of the Estate - 350 acres that had been under the plough since the Second World War. The park restoration provided a chance to look at the land in an entirely different way and suggested the possibility of rolling out nature conservation across the whole Estate.
The kind of conservation Charlie had in mind was a ‘process-led’, non-goal-orientated project where, as far as possible, nature takes the driving seat – an approach that has come to be known as ‘rewilding’. He was particularly keen to explore the ideas of grazing ecology promulgated by Dutch ecologist Dr Frans Vera, whose ground-breaking book Grazing Ecology and Forest History was translated into English from the Dutch in 2000.
In December 2002, Charlie launched his vision for rewilding Knepp by sending a Letter of Intent to Natural England, the government’s advisory body for the environment, setting out his plans to establish ‘A Biodiverse Wilderness Area in the Low Weald of Sussex’.
It took years for the idea to be wholeheartedly supported by the government, but in 2010, the Knepp Wildland project received Higher Level Stewardship funding. It is now a leading light in the conservation movement, an experiment that has produced astonishing wildlife successes in a relatively short space of time and offers solutions for some of our most pressing problems – like soil restoration, flood mitigation, water and air purification, pollinating insects and carbon sequestration. Visited by numerous conservation organisations, including the RSPB, Wildlife Trusts and the National Trust, as well as policymakers, farmers and landowners, Knepp is shaping the future of nature conservation.
As Professor Sir John Lawton, author of the 2010 Making Space for Nature report, says: “Knepp Estate is one of the most exciting wildlife conservation projects in the UK, and indeed in Europe. If we can bring back nature at this scale and pace just 16 miles from Gatwick airport, we can do it anywhere. I’ve seen it. It’s truly wonderful, and it fills me with hope.”
Keystone gardeners
In Knepp’s walled garden, it’s the gardeners who play this role as they prune, thin and weed (‘browse’, ‘graze’ and ‘rootle’).
Head gardener Charlie Harpur describes the approach as a form of ‘curation’ gently steering the plantings but otherwise allowing them to find their own way.
Decisions aren’t arbitrary since there’s a fine line between intervention and interference, so Harpur and his team work from an established set of criteria that they use to assess whether a particular species should be curbed or left to its own devices (aesthetics is an important criterion—perhaps the most significant difference from large-scale rewilding practice).
Harpur notes that ‘crawlers’ like Prunella and white clover need controlling; for example, since unmanaged, they are capable of establishing impenetrable, expanding patches that foreclose other dynamic processes.
Challenges and opportunities
The extent to which Knepp’s gardeners are able to allow the plantings to follow their own path is a testament to the skill and careful planning that went into the initial design of plant palettes, and the project is clearly a success in terms of both aesthetics and biodiversity (a recent survey revealed a 33 per cent increase in insect species richness over just three years).
It also speaks to a wider horticultural trend. The success of pollinator-friendly campaigns in recent years suggests a significant public appetite for a looser, more wildlife-inclusive approach to garden-making.
The challenge for horticultural producers is how to take advantage of consumers’ gradually shifting perspectives by finding a marketing language and strategy that balances the commercial emphasis on appealing, uniform and damage-free plant products with an acknowledgement of the full range of natural processes in which they participate.
Nectar-rich, pollinator-accessible species roses are an easy sell, but it’s hard to imagine hostas successfully marketed as the ideal food plant for slugs! Knepp’s experimental approach is truly food for thought.
