Hello Whatisnot, I wouldn't think the rocks would harm the rose bushes. The only thing I worried about was heat retention; darker colored stones especially, because they hold heat very well, which may raise the temp of the rose bed. We kept our roses well-watered and they did just fine. Let me know what happens, I see you are in Zone 4-5 too, so are we, only in WI. Has spring sprung for you yet? We're still shovelling snow. Karen

Hi whatisnot ~ I've never done that myself, however, a neighbor planted several roses on the curbside and covered the whole area with rocks. This is the third year and they are doing great.

Ed-