One of the hallmarks of a successful garden is the feeling that the whole ensemble — the walls, the terraces, the trees — has always been there.

Nothing jars, not the materials or the spatial qualities or the changes in elevation, so that the mind can simply take in its beauty and the deeper sense of well-being. This dichotomy, of something so considered that it is invisible, is probably why people generally don’t think about a garden as a designed space.

When they do, it comes as an epiphany of sorts. That’s what happened to Jo Thompson, who, in her 20s, was a teacher living in a tiny flat in London and wanted her rooftop terrace turned into something. She asked the local garden center to help “and this guy came over and started drawing things. I said, ‘What are you doing?’ It was a real lightbulb moment seeing this guy transforming my space on paper. Immediately I was hooked, absolutely hooked,” she said.

That chance encounter revealed her calling. Today, Thompson is one of the leading landscape designers in that hotbed of horticulture we know as England. She is so successful that she has the type of client list that remains non-disclosed, though many are creative types in the media, the movies, advertising and publishing. We know that she has worked for Sam McKnight, hair stylist to the stars and thus one himself, and for Cate Blanchett, who needs no introduction.

Thompson seems to have brushed the stardust off her as if it were dandruff. She is singularly low-key, soft-spoken and self-effacing. Some garden designers with A-list clients strut a bit. Thompson gets down to business. “I have no ego,” she said.

She recently appeared at the Silver Spring Civic Building in suburban Maryland before a group of more than 100 fellow garden designers, spending 90 minutes or so on a slide lecture of her work, much of it for the staged garden displays at the famed Chelsea Flower Show. The show gardens are inherently contrived — they are displayed in the grounds of a veterans home in London — but the sophistication of the designs and level of craftsmanship and plantsmanship elevate them beyond their setting. Nothing like them is seen in garden shows in the United States.

At Chelsea, Thompson’s designs are the opposite of her client commissions — they’re very public and popular. Her shelf is groaning with gold medals from Chelsea. For this year’s show, she is doing a much-anticipated garden titled Garden for Friendship.

Actual gardens need to draw from their settings, rather than impose upon them. In her talk, she showed a seaside garden that needed to relate to a very public beach while giving the owners privacy from it. This was achieved with a stylized dune landscape with sunken areas that afforded seclusion.

Some of the simplest fixes are the most elegant. She showed an old red-brick cottage with an ugly gravel driveway along the side of the house. She attached a screen, a high brick wall, to the edge of the house, and in one fell swoop, cleaned up the driveway area while establishing an enclosure for a secluded garden behind. The wall featured a gate fashioned from recycled boards, all very vernacular and congruous.

Her gardens seem neither avant-garde nor traditional in the English sense of color-schemed borders or impossibly rich medleys of herbaceous plants. She does rely on roses and box hedging, and the plant beds hew toward being soft and safe. “I want everything to be inviting and understandable,” she told me. “A successful garden needs an atmosphere. It doesn’t need to look as if it’s been there forever, but it needs to feel as if it should be there.”

If you want a Moroccan courtyard garden, “I’m not the person to ask,” she said.

Her talk was to the regional chapter of the Association of Professional Landscape Designers, whose members were no doubt already well aware of the forces that shape a designed garden — the limitations and opportunities of the site, the experience and talents of the designer, and the needs, tastes and budget of the client. The last component can be the hardest to address because the designer is trying to give form to something the client usually can only express ethereally.

“There’s a massive leap of faith that clients take,” she said. Her duty, she said, is to get an early sense of their aesthetics. “I like to spend a lot of time understanding their style, how they choose to live. Their likes and dislikes will come out.” Some of the signals come from how the clients decorate their homes. “I think a really good understanding of what they’re going to like will avoid a nasty surprise later on,” she said.

In some respects, she is in the same line of work as some of her artistic patrons — creating a stage, providing theater and presenting a narrative.

Lynley Ogilvie, a landscape designer in Arlington, said she was struck by just how much Thompson’s work is driven by the site and the client rather than a signature style. “I was very impressed with her range,” she said.

Maureen Robinson of Blue House Gardens, also in Arlington, said: “I think her gardens are just beautiful, with a looseness with the plantings.”

“I would think she’s very driven,” said Molly Scott, the chapter president, whose firm, Molly Scott Exteriors, is based in the District. “Not as relaxed as she comes across. And obviously very talented.”

But for the note-taking designers in the audience, the focus sharpened most when Thompson was talking about the crew she works with, how that fountain was constructed and what that erosion fabric was made from. Said Scott: “We are a very practical group.”

Tip of the Week

Ornamental grasses should get their annual chop now, cutting last year’s growth to a few inches above soil level. Sharp hedge shears are perfect for the job.

— Adrian Higgins

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