Jeff, absolutely, but all of this plantlore is well-used and understood throughout folklore and there is nothing hidden about it.

Ebbie, a useful book that looks at symbolism in the big ballads is Wimberley's 'Folklore in the English and Scottish Ballads' which though long out of print seems to be fairly easily obtained. You wouldn't have much problem getting a cheap copy on Alibris, Abe Books or Amazon.

Foolestroupe
Have you noticed how Johnson keeps whipping out his sword. Symbollock or not? NOT!