Sorry to come in late but just seen this thread.

eanjay -
In one version of Streets of Laredo roses are used to cover the coffin to stop the smell from the body of a young cowboy who died from a STD.

Surely you are mixing versions - the only line I have ever heard for SoL is 'shot in the breast'. Heard numerous versions but never about STD.
The 'Unfortunate Rake' (I believe thats the title) is about STD.

Bunch of Thyme I always thought referred to virginity.
In my innocence I assumed the roses were a means of seduction.