Here is a tip. If you use herbicide, protect your ornamental plants by holding a piece of cardboard against the grass. It will soak up errant spray. Don't recycle this cardboard; it should go in the trash.
If you need to kill grass growing close to ornamental plants, you can apply a selective herbicide that targets only grasses without harming your garden plants. These herbicides will kill most annual grasses like crabgrass and foxtails, as well as perennial grasses like quackgrass.