The garden, of course, is Eden, and the fact that it has gone wild is indicative of a post-lapsarian existence (later on the page there is a 'snaky looking' orchid). This wildness is not necessarily a moral negative: the garden has gone wild because the Cosways no longer have a slave workforce to tend to their land.
As Rhys's biographer, Carole Angier, notes: ‘colours are brighter, smells stronger; trees and flowers and insects grow bigger’. This superfecundity and sensuality of the Caribbean will account for much of the disorientation that Rochester feels within the book. See Jean Rhys, by Carole Angier.
Thomas Cole's 1828 painting of the Garden of Eden imagines it as a tropical paradise akin to a Caribbean landscape.