A row of barnlike sheds stands on Lorin Maazel’s farm in the rolling hills of Rappahannock County. They’re simple prefabricated sheds, the kind you can pick up at any home-supply store, decorated like miniature barns: the kind of sheds people set up in their yards to store the power mower, the mulch, the lawn tools. On Maazel’s farm, they contain high-quality Yamaha keyboards. They’re practice rooms for the young opera singers and instrumentalists taking part in the Castleton Festival.

They also have air conditioning. “The first week,” says Nancy Gustafson, an operatic soprano who finds herself in a role she hadn’t prepared for as Castleton’s general director, “everyone was coming to me going, ‘It’s really hot in there.’ We knew we were putting in air conditioning; we just didn’t have time to put it in.”

World-class music in Home Depot sheds: It’s the epitome of the Castleton Festival’s distinctive blend of the first-rate and the down-home. And it’s not what anyone expected from Lorin Maazel.

Maazel, 81, has long represented the most elite side of classical music: brilliant talent, an imperious manner and a reputation for not suffering fools lightly. No one questioned his musical genius; lots of people questioned the warmth in his performances. He headed some of the most renowned classical music organizations in the world: the Cleveland Orchestra, the Vienna State Opera and the New York Philharmonic, where he was music director from 2002 to 2009. His home in rural Virginia was a retreat fully in keeping with an elitist reputation: 550 acres of rolling farmland in an unspoiled and expensive area where he and his wife, the German actress Dietlinde Turban Maazel, raised three children and cultivated a literal menagerie including, after the zebra and donkey had been kept together in close quarters, a zonkey. When Maazel built a home theater, it was to present chamber concerts by the most famous musicians in the world — Emanuel Ax, Itzhak Perlman — for a select audience.

The Castleton Festival is showing a side of Maazel few people suspected was there. Its can-do, homemade spirit smacks of the fresh-faced naivete of Judy Garland and Mickey Rooney: “Let’s put on a show! There’s a barn out back!” For two months every summer, the family property is overrun with musicians. Maazel and his staff (that would be, largely, Gustafson) hand-pick a group of talented young artists — instrumentalists, singers, conductors — who come live on the grounds, work intensely with Maazel, and put on staged performances of opera and concerts for the public that rival the best of Washington’s professional offerings. The third season begins on Saturday with Puccini’s “La Boheme,” performed in a new pavilion Maazel has erected to replace the old festival tent. (“What bloom! What volume!” he says excitedly, of the pavilion’s acoustics.)

The Maazel family pitches in. Dietlinde works with Gustafson as an unofficial second in command. The youngest of the Maazel children, Tara, offers German coachings; Leslie, the second son, helps chauffeur members of the children’s chorus back and forth for rehearsals in a function they have dubbed “Maazel’s Limousine Service.” And Maazel himself, in blue jeans, can be found leading rehearsals two and three times a day, working nine hours in front of the orchestra, for no remuneration. Castleton’s budget this year is $2.5 million; until now, Maazel has been paying for almost all of it himself.

“This is our home,” Maazel says. “It’s supposed to be our retreat, so no one could ever find us when I’m not in some urban center conducting. And here we are,” as the festival gets underway, “in the middle of the world we thought we had escaped. But it’s different. This is really about young people and their aspirations and their dreams. I said to myself, midway through the first festival, ‘This is a privilege, Lorin. Forget about retreat; you can retreat to the manor house after everyone has gone home.’ ”

There’s no arguing the sincerity of someone who is willing to pay a couple of million dollars to train young artists. Maazel appears to be infused by a vision of the future, a desire to help spread music to the next generations of performers and audiences. (He avers that the average age of Castleton’s audience last year was in the mid-40s: strikingly low, in the classical music world.) The festival has also introduced a training program for college-age singers, who get lessons and coachings and do double duty as the opera chorus. Some of them pay tuition, but even full tuition, at $2,500, is cheap for the cost of lessons and room and board for a summer.

“I feel it’s an honor,” Maazel says, “to be in the position to introduce to the arts — an area to which I’ve devoted my life — young people who will in turn carry the torch into the future. It’s not an obligation; it’s an honor I’ve been given by fate. As long as we’re able to keep our head above water, I intend to go on.”

All of this work has yielded something quite special. In three years, Castleton has grown from a curiosity to one of the highlights of the area’s cultural year. It began, in 2008, with strong performances of Britten’s chamber operas in the Maazels’ diminutive home theater, and a few orchestra concerts in a temporary tent. Last year, it featured an impressive performance of Puccini’s three one-act operas known collectively as “Trittico,” triptych. This year, Maazel has turned his sights to “Boheme,” one of the most popular and some might say most hackneyed operas in the repertoire.

“I always feel Puccini has been one of the most misunderstood geniuses,” Maazel says. “Everybody loves Puccini, but often for the wrong reasons. There’s nothing sentimental about his music, or vulgar, or cheap.” “Boheme” is often presented as a kind of pageant; in the Metropolitan Opera’s beloved Zeffirelli production, it seems as though the whole city of Paris were brought onstage. At Castleton, by contrast, it will be intimate. “We’re talking about two sets of ill-starred lovers,” Maazel says. “Our production concentrates on just those four people. Yes, there are street scenes, but on the other side of the window. I want to throw into relief the intimacy of this opera: a chamber opera set in the large city of Paris.”

“Boheme” is only one facet of an exceptionally varied season. The program runs the gamut from Ravel’s magnificent chamber opera “L’Enfant et les Sortileges” on the Maazel estate to concerts at the new Hylton Performing Arts Center in Manassas (where offerings will include a concert performance of “Porgy and Bess” and an American program commemorating the Battle of Bull Run) to a gala benefit at Strathmore in which Jeremy Irons and Helen Mirren will narrate and enact scenes from Shakespeare, with full orchestra. When you’re Lorin Maazel and trying to raise money for your own festival, you can call in the big guns.

Raising money is itself an innovation at Castleton. The festival, Maazel observes, “started upside down. Most festivals begin with all the funds in place and then you start to plan. Since we had no intention of setting a festival into motion, we had no funds to collect.” Now, however, Maazel has bigger dreams for Castleton: dreams that will require more funding. In the long term, he’d like a larger permanent theater, and more money to bring in other high-profile artists to work with the young performers. He hopes to bring in some mid-career conductors who can grow with the festival and eventually, perhaps, step into his shoes. “A festival,” he says, cannot exist forever based on the energy and input of one person, financial and artistic.” This year, therefore, Castleton has added a director of development to its staff. But fundraising, Gustafson acknowledges, is slow.

And although Maazel insists that Castleton “is not the Lorin Maazel Festival,” the event’s significant strength is that it is. It’s Maazel who draws the highest caliber of young talent; Maazel who captures the attention of potential co-producers so that now, in its third year, Castleton has put on or is planning performances and productions in California; Toronto; Bari, Italy; and, this fall, Beijing (which will see the premiere of a “Barber of Seville” that will open Castleton here in 2012). It’s Maazel’s presence that sets Castleton apart from the Wolf Trap Opera, another very good summer-season program for young artists (Wolf Trap and Castleton have had several shared singers).

The question is whether Castleton can continue to develop as it solidifies its institutional underpinnings and becomes less, in effect, one person’s hobby. It’s still poised between its status as generous retirement project and new cultural force. (Maazel, incidentally, is a long way from retiring; in 2012, he will take over as music director of the Munich Philharmonic.)

But for long-time industry observers, the image of the imperious musician who led but was not beloved by such august institutions as the Cleveland Orchestra and the Vienna State Opera, now literally rolling up his i and giving his all to train the young, is eye-opening.

Maazel himself attributes the change to age.

“There are only two ways of growing older,” he says. “You can get more and more wrapped up in yourself, bitter and turned inward, or more mellow. The children I had whom I love challenged me to get out of my own shell. It takes life experience to shake us up.”

“I feel very fortunate,” says the once-forbidding maestro, “to be given by nature this tendency to be mellower and more cheerful.”