While Ernest Hemingway boils things down to the essentials, his friend William Faulkner lets the pot boil over, spilling onto the stove, down onto the floor, and maybe somehow catching the kitchen on fire.
With Faulkner we can feel the vines tangling, the magnolias blooming, the plants around Emily's house breeding, helping to hide her from the harshness of the world she lives in, a world in which she doesn't really belong. This tangling of blooming and breeding is replicated in the fancy words and long, complicated sentences for which Faulkner is famous.
Part of lushness is that other side of nature, the side we might not want to look at, and the side that's in store for everything in nature: death and decay. Faulkner never neglects this side (certainly not here), and with every blooming rose, he gives us a rotting one, too.
The lushness is also ironic, and perhaps a reaction against a lack of lushness. We know that although Emily's place was probably lush and overgrown, she never went outside to enjoy it, and only rarely even let in the light from outside. The story not only celebrates a lush life, by representing its opposite, but also cautions us against alienating others, against pushing others to hide from the light of life.