“I see grass growing in my garden beds with perennials and groundcover and find it frustrating to get rid of. The grass may have gotten a start in my beds after I seeded my lawn last fall. It’s hard to pull out and seems to keep coming back. What’s the best way to get rid of it? It seems to be spreading.”
– Alfredo Ramírez, Evanston
Grass is difficult to eradicate once established in the crowns of perennials and in beds of groundcover. One option is to uproot the grass continuously, beginning in early spring when you first see it and continuing to do so throughout the growing season. The best time to do this is when the soil is damp as it is easier to get the roots out and the more roots removed the better the results.
This requires a lot of patience and perseverance to be successful. Over time, the grass should weaken and eventually disappear. A weed puller with a forked end or a trowel is a good tool for getting the roots out. A weeder works better when space is tight and does less damage to surrounding plants.
Another option is to lift any perennials infested with grasses from the bed and carefully remove any grass from the plants’ root balls. Then dig up the remaining tufts of grass from the bed and replant the perennials. Watch out for grass that was missed during this process and will spring up again in the coming weeks.
This work can still be done on most perennials even though the time window 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, pull the weed as best you can and don’t let it go to seed.
There are herbicides that selectively kill grass in intercropping. Ornamec is an example of a herbicide that selectively kills grasses and can be applied over some ornamental plants. Read the label to determine if it’s safe to use with the plants in your garden. If any of the plants are not listed on the label, it is best not to use this product on the area. Or you can test it on a small section first to make sure it doesn’t kill or damage the plants you want. The best time to apply this product is when the grass is actively growing in spring and fall. These products are less effective in the summer heat when the grass is not actively growing.
Glyphosate, a non-selective, broad-spectrum herbicide, kills the grass as well as your garden plants. You can treat the grass that grows farthest from your desired plants by gently spraying the grass on a calm day.
To treat the grass that grows near the garden plants, first put on rubber gloves and then a cheap cotton glove. Using two fingers, dip the cotton glove in the herbicide and gently wipe the blades of grass, avoiding dripping onto neighboring garden plants.
It is important to read and follow all label directions when using chemical treatments.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at firstname.lastname@example.org. Tim Johnson is Senior Director of Horticulture at the Chicago Botanic Garden.