After more than five decades, landscape architect Gordon Riggle is still crafting Georgetown gardens. (Adrian Higgins/TWP)

I spent a lot of time in Georgetown gardens in the early 1990s for a book I was working on. It soon became evident that for all of the historic district's outward red-brick conformity, no two gardens were the same.

Some Federal-era mansions still had imposing and highly crafted gardens, all different, but it was the rowhouses built later in the 19th century that were, in some ways, more interesting. The outdoor areas were first formed as leftover spaces of utility — yards — and the challenge for landscape designers, when they arrived on the scene, was to create functioning gardens of privacy and beauty while bringing unity to disjointed spaces, some of them dark and cramped.

Among these smaller gardens featured in the book, some had been newly reworked by contemporary garden designers. They hewed more to limestone than brick and were less florid and more rectilinear. They were in every way edgier, and being somewhat callow and greatly enthusiastic, I was drawn to them.

Other town gardens were older, more conservative and inspired by Colonial Revival ideas of simple brickwork, geometry and boxwood enclosure. By the 1990s, they were period pieces: quiet, safe, graceful but old-fashioned.

Around this time I became acquainted with a landscape architect, Gordon Riggle, who had come to Washington in the early 1960s. He found himself under the wing of the masterful designer Perry Wheeler, a gardening pal of such tastemakers as Bunny Mellon and Jackie Kennedy.

One of Riggle's gardens was featured in my book ("The Secret Gardens of Georgetown"), an L-shaped lot created when an addition was built on a rowhouse. The rear space was defined by a swimming pool terrace. In the narrow side yard, Riggle built a Japanese-style viewing garden, to be enjoyed from indoors. The two gardens were separated by a moon gate.

The viewing garden was distinguished by fluid swirls of brick paving, moving like the incoming tide around upright Zen stones.

The brickwork's plastic quality recalled a garden by Wheeler that was also in the book. In an L-shaped garden of quite different character, more open and sunny, Wheeler had used brick, boxwood and Venetian statuary to create a little neoclassical jewel, a sitting terrace by the veranda, of perfect scale and felicity.

"Washington gardens are all derived from Savannah and Charleston," said Riggle.

Back in the 1990s, it would have been natural to think of Riggle's work as a vestige of an earlier age. But that would have been a misreading. He is a designer informed by that tradition, but he wasn't stuck in the past. As if to reinforce that, I received a letter from him earlier this month inviting me to drop by his latest Georgetown project.

This was a multifaceted garden around a Gothic Victorian house on 31st Street. He had installed it in the early 2000s, when the house was being renovated and its imposing side porch, once removed in a contemporary phase, returned.

The formal front garden was marked by an aerial hedge of clipped lindens. To the side, an elevated terrace was defined by a wall fountain and koi pond. The back side of the house, once the location of a small swimming pool, was now a boxwood knot garden in a frame of pea gravel. A hidden retaining wall allowed him to keep a trellis screen along the property line and to raise the rear lawn to a formal grassy panel. The alley beyond was screened with a row of Cleveland pears.

In such enclosed urban environments, the garden spaces must feel not just harmonious but also obvious, as if they had always been there. A big part of pulling this off is in the choice of materials and attention to detail. One of the key horticultural skills is the fine pruning of the trees. Perhaps because he is old school, Riggle involves himself in the construction of his gardens, whether it's guiding crane operators or placing grading stakes for the earth-moving machines.

At his garden in Fairfax, Va., he once taught me how to dig a root ball for an established boxwood to be moved, a procedure that includes the art of burlap wrapping and drum-lacing the ball.

In returning to the Georgetown garden, Riggle had been asked to simplify the space to reduce its maintenance burden. When I arrived, he looked much the same as he always had, tall, upright and wearing one of his trademark wide-brimmed Amish hats. His steps were more labored and shorter than I remembered. "I'll be 80 next year," he said.

His solution for the garden was to remove half the lindens and 150 linear feet of boxwood edging. He directed his crew to take out three of four Japanese cherry trees and to reduce the overgrown pears to high stumps, which will produce a flush of new growth next year. He also thinned the canopies of a number of trees that had grown thick over the past 15 years. Even after all this lightening, he noted, the garden still retains its essential elements and character. He designed it as an homage to a Parisian town garden.

The owner, Shannon Fairbanks, credits Riggle with "being able to create different rooms in a tiny space that are continuously showing themselves in a different way. I think that's the most enchanting aspect."

But seeing these adjustments was a reminder of the ethereal nature of things. The historic ambiance of Georgetown hides the fluid nature of the properties, the shifting interiors of the homes and the unstoppable aging of the gardens. Of those I featured in the book with the photographer Mick Hales, all have changed in some way, and some have been erased.

I couldn't help but think of the parallels between the scaling back of the Fairbanks garden and the winding down of Riggle's creative journey. We sat on a chilly terrace, warmed by reminiscence. "I have had a charmed life because so many people carried me along," he said. He arrived in town as a fresh-faced farm boy from Ohio and found himself at the center of the free world, when Georgetown was an intoxicating highball of society, politics and intrigue. Wheeler, an urbane Southerner, moved easily in these circles, at cocktail parties by night and in the gardens by day.

"I was very shy and didn't ask a lot of questions. I should have quizzed him more," Riggle said.

"You mean, on his design principles?" I asked.

"No," said Riggle, shaking his head just a little. "On the gossip."

@adrian_higgins on Twitter