From "Alex Campbell Live" - LP recorded in 1964 - sleeve notes, written by Eric Winter:
"Robert Tannahill's poem The Braes of Balquidder may or may not have preceded this delightful folk song. It is just as easy to believe that Tannahill reworked the folk song as it is to imagine that the folk process rounded off and re-beautified the poem. This version (from the McPeake family of Belfast) is not the Tannahill's poem, nor is betsy miller's lovely version. Both are lovely songs and the McPeake version is solidly established as an end-of-evening song in countless folk clubs."
And so what doid Alex sing (the McPeake version as it statess above)?

"And the wild mountain thyme,
All the moorlands is perfuming"

i.e it rhymes with blooming, and was how I learned it and sang it for years until I realised others were singing "grows around the blooming heather"