Naturalistic Planting: Lessons from Nigel Dunnett's Barbican

Why the Barbican Scheme Matters for Naturalistic Planting

The Barbican Estate is one of the most architecturally severe environments in Britain: raw concrete, deep shadow, hard surfaces on every side. When Nigel Dunnett, Professor of Planting Design and Urban Horticulture at the University of Sheffield, was commissioned to rethink its planting beds around 2014, he was not working with generous borders and deep, rich topsoil. He was working with shallow containers and raised beds, much of it over concrete structure, with perhaps 200 to 400 millimetres of growing medium at most. The kind of conditions that would defeat a conventional mixed border before it had even got started.

What he produced is, in my view, one of the finest examples of naturalistic planting in a British urban context. The beds are alive with colour across most of the year. They support extraordinary levels of pollinator activity. They are genuinely beautiful, not in a manicured, high-maintenance way, but in the way that a well-composed meadow is beautiful: full of movement, layered, slightly unpredictable, always doing something interesting. And they function on minimal irrigation, minimal fertiliser, and relatively light maintenance. That combination is not accidental. It is the direct result of a coherent, evidence-based design philosophy.

The Engineered Substrate: Hungry Soil as a Design Tool

The foundation of Dunnett's approach at the Barbican, and in his wider research, is the soil itself. This is the part that surprises most people when they first encounter it, and it is the principle I find most valuable when I apply it in Kent gardens.

Convention tells us to improve our soil: add compost, increase fertility, create the richest possible growing medium. Dunnett's research, much of it developed at Sheffield's experimental green roof and urban horticulture plots, suggests a different logic. For naturalistic, low-maintenance planting composed of drought-tolerant perennials and grasses, a lean, free-draining, low-nutrient substrate is not a compromise. It is a design decision. Hungry soil suppresses the vigorous, thuggish species that would otherwise swamp a more delicate planting. It favours the prairie-origin and steppe-origin plants that form the backbone of contemporary naturalistic schemes: species adapted over millennia to thriving in difficult conditions, growing slowly and steadily rather than explosively, flowering prolifically because that is how they attract pollinators in a competitive landscape.

At the Barbican, the substrate mixes used are light, free-draining and deliberately nutrient-restricted, which also matters practically for beds over concrete structure, where weight loading is a constraint. The plants chosen are matched to those conditions from the outset. The result is a planting that is, in ecological terms, in balance rather than constantly straining against an overly rich environment.

This is a lesson I apply directly in my own work. On the sandy soils of the greensand belt south of Sevenoaks, and on some of the thinner chalk-influenced soils along the North Downs, the conditions already tend in this direction, and naturalistic planting schemes perform beautifully without significant amendment. On the heavier Weald clay that I encounter so often around Edenbridge and Tonbridge, the approach has to be adapted, but the underlying principle holds: do not automatically reach for the bag of compost. Work out what the plants you are specifying actually want.

The Plant Palette: Perennials, Grasses and the Matrix Approach

Dunnett's planting palette at the Barbican draws heavily on the prairie and steppe flora of Central Europe, North America and Central Asia. These are not exotic choices in the horticultural sense; most have been in cultivation for decades and many are readily available. What is distinctive is how they are combined and in what proportions.

The matrix planting approach, which Dunnett has developed alongside colleagues including Hitchmough at Sheffield, works by establishing a ground-layer matrix of low, tough, spreading plants, usually grasses or sedges, through which taller structural perennials are woven at calculated densities. The matrix suppresses weeds by occupying every available square centimetre, while the structural plants provide the seasonal drama and height variation that gives the planting its character.

At the Barbican, you will find species such as Stipa tenuissima (now correctly Nassella tenuissima), the fine-leaved feather grass that catches light with extraordinary grace, alongside drought-tolerant perennials including Echinacea species, Rudbeckia fulgida var. sullivantii 'Goldsturm', Penstemon, Agastache, various Salvia species, and the flat-headed Achillea cultivars that are so valuable for pollinators. Alliums provide the vertical punctuation in late spring. Ornamental grasses including Calamagrostis × acutiflora 'Karl Foerster' carry the structure into autumn and winter when almost everything else has died back.

The result is a planting that gives a genuine season of interest from April through to February, when the bleached seedheads and grass stems are finally cut back. That twelve-month arc is not incidental. Dunnett designs for it deliberately, selecting plants whose dormant structures are as considered as their flowering performance.

Wildlife Value in an Urban Setting

One of the arguments I find myself making more often than any other to clients across Kent is that a planting designed primarily for naturalistic beauty and low maintenance almost always turns out to be a planting designed for wildlife, whether that was the explicit intention or not. Dunnett's Barbican scheme demonstrates this with particular clarity.

The diversity of flower form, flowering period and plant architecture across the scheme provides nectar, pollen and larval habitat for a remarkable range of invertebrates in an environment that might at first seem inhospitable to them. Deep in the city, surrounded by concrete, the Barbican planting has become a genuine ecological resource. The free-draining substrate also creates the bare-soil habitat that many solitary bee species depend on for nesting, which conventional garden mulching destroys.

I see the same dynamic in Kent gardens where I have specified similar naturalistic schemes. A client near Westerham whose south-facing border I replanted three years ago on deliberately lean, free-draining soil with a grass-and-perennial matrix now reports bees, hoverflies and butterflies in numbers she had not seen in her garden before. The planting is also, not coincidentally, the most admired part of her garden by any visitor.

What Homeowners Can Borrow from This Approach

You do not need a concrete housing estate in EC2 to apply what Dunnett has demonstrated. The principles translate directly to a garden in Sevenoaks, Bromley or the Darent Valley with relatively small adjustments.

Resist the urge to enrich. If you have a free-draining, relatively lean soil and you are considering a naturalistic planting, leave it alone. Replace any impulse to add general fertiliser with an honest audit of what the plants you want actually need. Most steppe and prairie perennials will reward you for it.

Think in layers, not in rows. The matrix approach is more forgiving to establish than it first appears: plant the grass matrix first at relatively close spacing, then introduce the structural perennials through it as gaps allow. The two layers support each other and the weed suppression is far better than in a traditionally spaced mixed border.

Design for winter as deliberately as for summer. The grasses and seedheads that carry a naturalistic planting through January and February are not a consolation prize. Dunnett's Barbican beds in midwinter, with their bleached Calamagrostis wands catching low light above the frosted seedheads of Echinacea and Rudbeckia, are among the most photographed aspects of the scheme. Build that layer in from the start.

If you would like to discuss how a naturalistic planting scheme might work in your own garden, I would very much welcome the conversation. My studio is in Eynsford, and I design gardens throughout Kent and into South East London. You are welcome to get in touch through my website, and I look forward to hearing about your garden and what you are hoping it might become.