According to Jamie McIntosh, when grass invades flower beds, a selective herbicide is the best product for killing it without harming the flowers. Grass Beater and Grass-B-Gon are the most popular herbicides for targeting and killing grass. They kill off annual bluegrass, bentgrass, bermudagrass, crabgrass, downy brome, foxtails, goosegrass, Johnson grass, panicum, quackgrass and sandbur.
Select herbicides are formulated for grassy weeds and are designed to leave flowers, shrubs, ornamental plants and ground cover plants unharmed. They often require repeat applications to completely kill the grass. Due to brand differences, always check before buying to make sure the selective herbicide targets the right type of grass while leaving other plants intact.
Broad-spectrum herbicides may also be used, but if they come in contact with flowers, seeds or other plants, they indiscriminately kill them all. The only way to use broad-spectrum herbicides is to cover intentional plants with buckets or surround them with cardboard. Apply the broad-spectrum herbicides directly onto the weeds with a sponge or paint brush and do not apply on windy days. The benefit to broad-spectrum herbicides is their power to kill off any type of grass or weed that causes problems.
Avoid unwanted grass in flower beds in the future by creating a deep and wide border to the flower bed. Be careful when sowing grass and mowing so that no seeds or cut grass are flung into the beds.