English Art/Literary Botany Lyrics of the song Clementine, Pete Seeger version

There's a churchyard on the hillside,
Where the flowers grow entwine.
There grow roses amongst the poses,
Fertilized by Clementine.

The word "poses" doesn't make any sense, when thinking about the conventional meaning of a pose or poses. So this obviously has nothing to do with posture or bragging. This is probably something physical, tangible, which is intermingled with roses in a rose garden. Could be some spots, holes, rows or some parts of a grid. Could also be some weeds among the roses. I have no idea, so I need someone to say with certainty, what this is.

Native speakers of American English only, please! Familiarity with cowboy songs a plus.
Thank you!