Dear Frank and Mary,
I have researched the "God's Garden" poem since finding a misquoted version of the 4th verse on a garden sign in Stratford, Ontario, Canada. It was wrongly attributed to St. Fiacre, the patron saint of gardeners.
I now have a copy of the poem handwritten on an envelope in England, circa 1925, which has the four verse version. It adds the information that the poem was inspired by the exquisite garden of Lord Ronald Gower, at Hammerfield, Penshurst, Kent, and that it was originally written by Mrs. Gurney in his visitor's book. I have posted this information to her page on Wikiquotes. Other information I have found suggests the visit was some time in 1901-2.
According to the information I have, it would appear that the fifth verse was added later, since it only seems to have survived in a later Hymn version. Hymns are usually indexed by the first line, e.g. "The Lord God planted a garden," so the published title remains "God's Garden." However, I have not yet found this hymn version on any of the internet hymn sites, which do include her hymn "O Perfect Love." The final word would come from a copy of the 1902 sheet music. Until then, it is also possible that the fifth verse, which is somewhat obscure, was edited out before the poem appeared in her 1913 book of poems.
I hope this is still of interest,