Summer in the city: garden designer transforms south-London rooftop with putting green, outdoor kitchen and 18-seat dining table

On the seventh floor of a converted warehouse near Tower Bridge is a rather wonderful and private garden, custom made for dining, entertaining and enjoying the panoramic skyscape.

The entire space is substantial — almost 40ft by 50ft — but whereas previously it comprised shabby decking and a few pot plants, now there is an outdoor kitchen, a generous seating area with weatherproof sofas, a dining table that expands to seat 18 and a carpet of lawn which acts as a rooftop putting green.

Garden designer Katharina Nikl was called in by the American owners to provide a series of outdoor rooms with easy-care planting. Unusually, there was already a greenhouse, which provides shelter on cold but sunny winter days, so Nikl designed the rooms around the glass building, in a U shape.

She replaced the worn decking with durable ipe hardwood that, by laying the boards horizontally or vertically, delineates each space. The “chill” area of three sofas and glass-topped coffee table is further defined by a band of decorative pebbles hiding a drainage channel.

Cedarwood panelling along the back of the roof garden, behind the central sofa, creates instant privacy from the neighbours, protects the seating area from the wind, and will eventually be covered by evergreen jasmine.

At the opposite end of the roof garden, Nikl rolled out an artificial lawn that will stay permanently green and maintenance-free.

There is also seating of two stools and dining chairs, but she designed a built-in bench to run along the length of a raised bed that is currently a mass of tulips. “I insisted on extra seating,” says Nikl, “because that way, when the sun travels around the space, you can follow it around. And a long, floating bench like this takes up little space, yet is invaluable for entertaining.”

In one corner, near the dining table, a long, lean hardwood surface with storage space beneath and a permanent barbecue on top serves as a food prepping area. Nikl designed rows of shelving for the wall above, but the clients, who are art lovers, decided to sacrifice the wall space for a bold painted mural by friend and artist Lauren Mele.

Aside from an acer salvaged from the original potted plants for its deep purple foliage, Nikl chose relatively drought-proof Mediterranean plants. But she installed an irrigation system so there’s no need for watering.

The long raised bed holds olive trees, cistus, rosemary, sage and ornamental grass Stipa tenuissima, which swishes and sways with the wind. “The two olive trees are still quite small, but they will establish better than large trees, which are subject to windrock,” says Nikl.

In spring, tulips fill the bed, and in summer, the purple lozenge heads of Allium sphaerocephalon draw bees and butterflies.

Lightweight faux-lead troughs — weight is an issue on rooftops — hold clipped box balls along one end of the space. On the other, behind the sofas in the shade, they are prettily planted with white hydrangeas and trailing ivy. “Lighting is one of the most important features in a city roof garden,” says Nikl. “When you entertain in the evening you need light, but you don’t want to fight the city lights. There’s a fine balance.”

She used three kinds of lighting: “Purpose lighting for the outdoor kitchen, which has to be at the right angle, so you’re not standing in your own shadow when you’re prepping food. Mood lighting to enhance the planting, comprising uplighters in the raised bed at the foot of the olive trees and tall grasses. Lastly, safety lighting that subtly skims across the floor so people can walk around without fear of stumbling.”

Transforming the garden took six weeks, and the trickiest part, says Nikl, was the logistics of moving out the old, and bringing in the new. “The clients had just moved in and didn’t want to upset the neighbours. We called in a Fulham-based company, The Garden Builders, who are used to this kind of sensitive work in London, and they used a hoist lift. We had one day to get everything out, and the next day to get everything in. It was hair-raising, but it saved a lot of disruption and hours of traipsing through the building.”

Katharina Nikl can be commissioned on katharinanikllandscapes.co.uk