Usually, having two differing locales – like the lavish London of the nineteenth century and an unspoiled countryside estate – would show readers a marked contrast. It usually goes like this: the urban center of London is the heart of England – full of business, fashion, culture, and general decadence – while quaint Hertfordshire would be an Edenic oasis where man can get close to nature and distract himself from the rush of city life.
But Wilde is parodying Victorian high society – which Jack buys into, both in London and in Hertfordshire. Indeed, both Jack’s city home in the Albany and his country home display the same opulence. Thus, the distinction between the corrupt city and the innocent countryside is lost. Indeed, the same frivolous tone established in the city transfers directly over into the country estate. We don’t see a contrast between the city-dwellers and the country folk; we don’t see the city’s concrete, marble, and soot set against the country’s green groves and flower gardens. Indeed, the same luxury that defines Algernon’s home on Half Moon Street (where Act I takes place) is present in Jack’s Manor House. Act I and Act III are both set in separate "Morning-rooms" – the first in Algernon’s London home and the other in Jack’s Manor House.
Only the second act takes place outdoors among the yew groves and rose gardens. But even outdoors, Wilde doesn’t emphasize the natural beauty of the place. Instead, he uses details like the flowers as ornaments – pretty little trinkets that aren’t really necessary to the story, but set a flippant mood, just like Algernon’s piano music does in the first act.
To emphasize this point, remember that Cecily is constantly watering the roses and that Algernon later compares Cecily to a "pink rose" (II.75). So the roses function as part of Cecily’s fantasy – not only as a pretty background for her daydreams, but as a way to highlight her beauty. In another telling instance, Gwendolen tries to insult the countryside by referring to the flowers, while having tea with Cecily. Cecily turns the situation back on Gwendolen by remarking that "flowers are as common here, Miss Fairfax, as people are in London" (II.306). In the process of insulting Gwendolen, Cecily also reveals that she thinks of the flowers as inhabitants of her rural world, much like crowds of people inhabit Gwendolen’s world.
Why does Wilde do this? Why can’t the Manor House and its residents be simple, pure, and earnest when compared to the city-dwellers? Well, the problem is that Jack and Cecily have much the same agenda as the urban aristocrats do. They educate themselves as well as they can to improve their prospects for the future. Cecily is just as concerned about her beauty and fashion as Gwendolen is. Indeed, Cecily and Gwendolen are foils. (See "Character Roles" for more details on this.) And there’s the problem that Jack is essentially the same person as Ernest. Thus, he has the same questionable morals in the city as in the country. Even the respectable Miss Prism has a shady past involved with Lady Bracknell in London. So Wilde makes the country setting just as playful and frivolous as the city one. He makes his point that Victorian nobility maintain the same values – like fashion, flirtation, and general frivolity – no matter where they are.