Grass in a perennial bed is certainly an unsightly nuisance. But did you know that it also competes with your perennial flowers for water and nutrients? Grass in a perennial bed should be killed as soon as it crops up to prevent further spreading. However, resorting to herbicides to kill grass is inadvisable. Herbicides are difficult to apply with accuracy and can harm your perennials and make your garden a toxic place to work
Stick your trowel 4 inches into the ground next to a clump of grass. Uproot the clump in its entirety (or as big a section as your trowel can manage).
Place the uprooted clump on a piece of cardboard.
Grab the blades of grass growing out of the uprooted section of soil. Hit the soil against the cardboard to remove any excess dirt.
Throw the grass clump and any clinging dirt into the bag.
Upturn the dirt next to the grass you removed to look for any remaining grass roots. Toss them into the bag as you find them.
Repeat steps one through five until all of the grass in your perennial bed is removed.
Check the dirt that remains on your cardboard for any roots. Toss any that you discover into the bag.
Return the de-rooted dirt to the perennial bed. Fill any low spots in your perennial bed with aged compost.
Throw the contents of the bag into the compost bin. This will kill the grass.
Keep grass out of your perennial bed for good. Stick a garden header around the border of your garden, at least 8 inches deep into the soil. This will keep your lawn from creeping into your flower garden. Then, spread 1 inch of organic mulch over your perennial bed to prevent grass from taking root.