Following a decade of steady growth in which everyone learned where to put the picnic basket and how to be first out of the car park, country house opera is entering a new phase. Garsington, near Oxford, has to find a new home at the end of the 2010 season. The name will remain and this week a private donor offered a substantial grant guaranteeing the company’s immediate future.

Its founder, the late Leonard Ingrams, had a passion for rarities but never got round to Vivaldi, who by his own boast — certainly exaggerated — wrote 94 operas, all forgotten. A Garsington mini-series began this year with L’incoronazione di Dario, in which the Emperor’s daughter improbably has three suitors and a little sister from hell.

All Vivaldi’s music, despite its bristling, tuneful energy, sounds to me indistinguishable from the Four Seasons. It churns on cheerfully and relentlessly, with a formulaic pattern reminiscent of Indian ragas. Lawrence Cumming conducted with persuasive flair and imagination. David Freeman, directing, and designer Dan Potra, opted for 1960s slapstick and tickle, giving the characters more acute personality than the music affords.

One suspects this is repertoire whose performing tradition we don’t yet fully understand. The same was true of Handel 30 years ago so we’d be wise to be patient. The excellent cast, led by Paul Nilon, Renata Pokupic, Wendy Dawn Thompson and Russell Smythe, gave a vibrant, polished account. With Rake’s Progress to come, and a first-class revival of Cosi fan tutte under way, Garsington is in rude health.