Frank Cabot, a blue-blood financier who became one of the world’s leading garden preservationists, died Nov. 19 at his family estate at La Malbaie in the Laurentian Mountains of Quebec.

Mr. Cabot, 86, died from idiopathic pulmonary fibrosis, said his son, Colin.

A tall, bow-tied, patrician figure who became increasingly engrossed by horticulture, Mr. Cabot founded the Garden Conservancy in 1989 to identify and preserve important gardens in danger of being lost after their creators died.

Since its inception, the organization has helped to sustain nearly 100 gardens of cultural and horticultural significance in the United States, such as the gardens on Alcatraz Island off San Francisco and the Longue Vue House and Gardens in New Orleans.

Other regional organizations existed to preserve historic gardens, but Mr. Cabot wanted the conservancy to be a nationwide force to protect newer gardens created by exceptional contemporary plantsmen.

The conservancy’s formation itself became “a turning point for American gardens” by directing the spotlight on the country’s horticultural jewels, said its president, Antonia Adezio.

Mr. Cabot (pronounced “Cabit”) by then was well on his way to finishing two gems himself. Near Cold Spring, N.Y., he spent more than 30 years developing Stonecrop as 12 acres of hillside display gardens that include woodland gardens, naturalistic rock outcroppings, ponds and enclosed English-style flower borders. It opened to the public in 1992.

His magnum opus was the design and construction of the gardens at Les Quatre Vents, the family property 90 miles northeast of Quebec City inhabited by his ancestors since the 1840s. Between 1970 and 2000, he transformed the landscape into a series of alternately grand, charming and intimate garden spaces that drew from decades of visiting gardens and learning from gardeners.

“The most interesting people in any community are the most serious gardeners, he found that to be true,” Colin Cabot said of his father.

Francis Higginson Cabot Jr. was born in New York City on Aug. 6, 1925. He served in the Army Signal Corps at the end of World War II, in both France and Japan. He graduated from Harvard College in 1949 and joined his father’s investment banking firm the following year.

He later became a partner at Train, Cabot and Associates, an investment and venture-capital business from which he retired in 1976. During periods of financial reversals and stress, he found succor in gardens and his interest gradually deepened into a second career.

He moved to Stonecrop in 1958, where he became an enthusiast of rock garden and alpine plants — the property is named for a genus of succulent. Mr. Cabot later was chairman of the New York Botanical Garden and became active in other public gardens in the city. At Wave Hill gardens in the Bronx, he met Adezio and the now-retired horticultural guru Marco Polo Stufano.

Mr. Cabot was drawn to anyone who shared his gardening sensibilities. “He had a rare quality coming from a privileged background,” Stufano said. “He really met people head on for who they were and what they knew and what they did. When he came to the potting shed, everyone loved it. He had a great respect for anyone who did their job well.”

Survivors include his wife of 62 years, the former Anne Perkins; three children, Colin Cabot of Loudon, N.H., Currie Barron of Boulder, Colo., and Marianne Welch of Prospect, Ky.; nine grandchildren; and five great-grandchildren.

In the late 1980s, while visiting gardens in California, Mr. Cabot made a side trip to the garden of Ruth Bancroft, who had put together a masterful arrangement of cactus and other succulents and arid plants over three decades.

The plant palette wasn’t to Mr. Cabot’s taste, but he was struck by the beauty and setting of the garden and worried about what would happen to it after Bancroft died. “My mother said, you should start a garden conservancy,” Colin Cabot said.

Frank Cabot and Adezio set up the organization in an office in Cold Spring. Mr. Cabot’s Rolodex was full of like-minded donors who saw the value of the enterprise and helped sustain it over the years.

At Les Quatre Vents, Mr. Cabot developed a garden of meadows, woodlands, allees and hidden spectacles that together directed a series of dramatic moments.

From his beginnings as a rock garden enthusiast, with sedums, primulas and lewisias the size of a pin cushion, he moved to gardening on the grandest of scales. The signal feature in the Quebec garden, which he called the Pigeonnier, is a replica of a French dovecote. Framed by clipped lindens, it sits Taj Mahal-like in a reflecting pool long enough to mirror the whole structure. Its bottom arch directs views to the St. Lawrence River valley.

His 2001 book, “The Greater Perfection,” gives his account of making the garden. The title comes from an essay by Francis Bacon, who argued that the civilized man first builds houses and then gardens, “as if gardening were the greater perfection.”