“I am seeing grass growing in my garden beds with perennials and groundcovers and am finding it frustrating to get rid of it. The grass may have gotten a start in my beds after I seeded my lawn last fall. It is difficult to pull out and seems to consistently come back. What is the best way to get rid of it? It seems to be spreading.”
— Alfredo Ramirez, Evanston
Grass is difficult to eradicate once it gets established in the crowns of perennials and in beds of groundcovers. One option is to keep pulling out the grass, beginning early in spring when you first see it 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 are removed, the better the results.
This will take lots of patience and persistence to be successful. In time, the grass should weaken and eventually disappear. A weeder with a forked end or a trowel is a good tool to help get the roots out. A weeder will work better when space is more constricted and will do less damage to surrounding plants.
Another option is to lift all the perennials infested with grass out of the bed and carefully remove any grass from the root balls of the plants. Then dig the remaining clumps of grass out of the bed and replant the perennials. Monitor for any grass that was missed during this process that sprouts again over the coming weeks.
This work can still be done now with most perennials, though the window of time is closing. You can also wait until the weather is cooler in early September or next spring before using this technique to reduce stress on the plants. If you decide to wait, then pull the grass as best you can and do not allow it to go to seed.
There are herbicides that will selectively kill grass in mixed plantings. Ornamec is an example of an herbicide that selectively kills grasses and can be applied over some ornamentals. Read the label to determine if it can be used safely with the plants in your garden. If any of the plants are not listed on the label, it is best to avoid using this product for the area. Or, you can test it first on a small section to make sure it will not kill or damage desirable plants. The best time to apply this product is when the grass is actively growing in spring and fall. These products will be less effective in the heat of summer, when the grass is not actively growing.
Glyphosate, a broad-spectrum, nonselective herbicide will kill the grass, as well as your garden plants. You can treat the grass growing the farthest away from your desirable plants by spraying the grass carefully on a calm day.
To treat the grass growing close to the garden plants, 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, avoiding any drips on adjacent garden plants.
It is important to read and follow all instructions on labels whenever applying any chemical treatments.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at email@example.com, Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.