re: Is there something that kills grass but not shrubs/plants?

You can use herbicides with the ingredients clethodim, sethoxydim, or fluazifop-p which will kill grass but not damage flowers and shrubs. Or use organic methods like vinegar, boiling water... Then, you can cover the soil of the flower bed with a 3 inch layer of mulch to discourage grass seeds from germinating. You can also use landscape fabric, but it's too time consuming imho.