Remember the secret garden Daisy finds at the house in the countryside her first day there? And how, like dear Cousin Edmond, it is neat, organized, and "surrounded by high brick walls" (1.3.8)? Just as Daisy looks at Edmond as a beautiful enigma hidden by mysterious walls, the garden's serene, innocent beauty is protected by strong, structural defenses. The garden is filled with "tons of flowers blooming already all in shades of white" (1.3.8)—and we don't need to be rocket scientists to figure out what white symbolizes (hint: it's not evil).
The garden, then, represents Edmond. Sweet, innocent, ripe-for-the-picking Edmond.
When Daisy returns to the garden after the war, however, the walls are covered with "climbing roses… just coming into bloom" (2.4.17), and "great twisted branches of honeysuckle and clematis wrestled each other as they tumbled up and over the wall" (2.4.17). Pretty different image, right? Gone is the orderliness of the garden when she first finds it, replaced now by a sort of overflow of blooms. The words "twisted" and "wrestled" indicate a kind of chaos to all this, instead of simple beauty.
The flowers now are "spread open too far, splayed, exposing black centers" (2.4.17), which is pretty different from the innocent, organized white rows of petals that used to inhabit the garden—those black centers let us know there's a darkness inside them. Even Daisy realizes the connection between the state of the garden and Edmond's mental state, noting:
I've never had my own garden but I suddenly recognized something in the tangle of this one that wasn't beauty. Passion, maybe. And something else. Rage. (2.4.17)
Who tends the garden? Why Edmond, of course. And while he's still beautiful to Daisy, he's also severely damaged by what he's seen and survived—he's no longer simply a blooming white flower, but one encircling darkness.