“Grass has started growing in a couple of my ground-cover plantings and in some sections of my perennial border. Some of the perennials with grass growing in and around them are lady’s mantle and astilbe. What is the best way to go about getting rid of this grass?”

— Juan Patino, Highwood

Grass is difficult to eradicate once it gets established in the crowns of perennials and beds of ground covers.

One option is to keep pulling out the grass, beginning early in spring and continuing throughout the entire growing season. The best time to do this is when the soil is moist, as it will be easier to get the roots out, and the more roots that get removed by pulling, the better the results will be. The grass will often just break off at ground level when the soil is very dry.

This will take a lot of patience and persistence to be successful. Over time, the grass should weaken and eventually disappear. A weeder with a forked end or a trowel would be good tools to use for certain situations and helpful in getting roots out.

Herbicides will be difficult to use in these situations due to the proximity of the desirable plants. Glyphosate, a broad-spectrum, nonselective herbicide will kill the grass, as well as the lady’s mantle, astilbe and ground covers.

You can carefully spray the grass growing away from the perennials to avoid contact with the herbicide on a calm day to avoid drift. For the grass growing close to perennials, put on rubber gloves first and then a cheap cotton glove second. Using two fingers on the cotton glove, dip into the herbicide and carefully wipe the blades of grass, taking care to prevent any herbicide drips on adjacent good plants. This work also is rather painstaking and not feasible on a big scale.

Ornamec is an herbicide that selectively kills grasses and can be applied over some ornamentals without damaging them. Read the label to determine if it can be used with the plants in your garden.

Lady’s mantle and astilbe are not specifically listed on the label of Ornamec, so you would need to test it first on a small section to make sure it will not kill or damage these perennials. The best time to apply this product would be when the grass is actively growing in spring and fall, so currently, the timing is not good to use this herbicide.

It is very important to read and follow all instructions on labels before using chemical products in your garden.

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.