Certified GKH Gardening Expert
Most grass in garden beds can be easily pulled up (though it may be time consuming) and followed with the addition of a 1/2" thick layer of (moist) newspaper topped with 2" mulch. You can also use a non-selective herbicide, such as glyphosate (Roundup), which has the potential to kill any plant on contact. However, with care this can be used as a spot spray in flower beds, avoiding contact with desirable plants. Don't do this on a windy day. If feasible, you might want to cover your candy tuft with trash bags while you spray, and for about half-an-hour after. It will dry rather quickly, kill the grass, and will not stay in the soil.