Likewise hemp: its use in song seems to be confined to cockroaches.

Apparently you've never listened to any reggae. :-) There are scores and more of songs about the herb, ganja, collie weed, sensimilla, sensi, chalice pipes, spliffs, etc etc.

What may be interesting is that many are not simply 'praising' the drug --i.e. as per one of the above ideas that some songs praise while others deride. These songs are not saying (like typical alcohol songs), 'Hurrah! Let's go get some pot/booze. It will be really fun.' Rather, the herb signifies (in part) a sort of resistance. I don't use ganja, but I can still vibe with the subversive tone of many of the songs.

This one has an especially militant feel:

Black Uhuru - Stalk of Sinsemilla

The narrator has "a stalk of sensimilla growing in his backyard." It's really a defiant statement.