London and Hertfordshire, England, in the Late 19th Century (The Victorian Era)
This might seem like a play that uses ye old City Mouse vs. Country Mouse squabble. But Wilde is too clever for that.
Usually, having two differing locales (like lavish London 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 is an Edenic oasis where man can get close to nature and distract himself from the rush of city life.
But Wilde is parodying the Victorian high society that these characters buy into, both in London and in Hertfordshire. Actually, both Algernon’s city home and Jack's country home display the same hoighty-toighty style. Because of this, the distinction between the corrupt city and the innocent countryside is lost.
In fact, the same frivolous tone established in the city transfers directly over into the country estate.
Only the second act takes place among the yew groves and rose gardens, but 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.
Remember that Cecily is constantly watering the roses and that Algernon later compares her to a "pink rose" (II.75). So the roses function as part of Cecily’s fantasy—they're both a pretty background for her daydreams and 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). Oooh. Burn.
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.
And there’s also the problem of Jack being essentially the same person as Ernest. He has the same questionable morals in the city as in the country. Even the respectable Miss Prism has a shady past involving Lady Bracknell in London. So Wilde makes the country setting just as playful and idiotic as the city one. He makes his point that the Victorian upper-crust maintain the same values—like fashion, flirtation, and general frivolity—no matter where they are.