Each year I get a lot of seasonal weeds in the flower beds, easy enough to pull out, was wondering if cgm would not be any good in a flower bed, any detrimental side effects?
No side effects except excessive greening of the plants. I would use mulch. CGM does nothing but fertilize for me.
If you have flowers that re-seed themselves, it might interfere. Although, as David notes, that might not be as big of an issue as some claim.