Some areas in my ground cover and perennial beds have become infested with grassy weeds. What is the best way to clean these areas up?
— Mona Herrera, Waukegan
I can relate to your frustration in trying to get grassy weeds out of densely planted beds. They are easier to remove in open bed areas. Grassy weeds are difficult to eradicate once they get established in the crowns of perennials or mixed in with ground cover beds. One option is to keep pulling out the grass, beginning early in spring and continuing throughout the entire growing season. This type of weeding thoroughly tests my patience as the progress is slow and success requires persistence in weeding month after month. The best time to
do this is when the soil is moist and it is easier to get the roots out. The more roots are removed, the better the results. This takes patience and persistence. In time, the grass should weaken and eventually disappear. You can use either a weeder with a forked end or a trowel for this purpose.
A non-selective herbicide is difficult to use in this situation because desirable plants are nearby. Glyphosate — a broad-spectrum, non-selective herbicide — kills the grass as well as all the other plants it touches. To treat the grass growing furthest away from the good plants, spray the grass carefully on a calm day. For the grass growing near ground covers, perennials and bases of shrubs, put on rubber gloves with a cheap cotton glove on top. Using two fingers of the cotton glove, dip into the herbicide and carefully wipe the blades
of grass, avoiding any drips. Consider killing entire bed areas where grassy weeds are particularly bad and starting over with a new planting. Digging all the plants up is another method if you prefer not to use an herbicide.
Ornamec and Poast are herbicides that selectively kill grasses and can be applied over some ornamentals. Unfortunately, these two products have limited effect on bluegrass. They cause yellowing but do not typically kill the grass. Read the label to determine if it can be used safely with the plants in your garden. You may want to test it first on a small section of ground cover planting to make sure it will not kill or damage ground cover. The best time to apply this product is when the grass is actively growing in spring and fall. It is extremely important to read and follow all instructions on labels.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.
