Grass has found its way into my garden bed that has ground cover and perennials. I am very frustrated that this area of my garden has gotten away from me. How can I get rid of the grass in these areas?
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— Alex Davos, Waukegan
Weeding grass that has gotten mixed in with other plants is one of my least favorite gardening tasks, as it takes a lot of patience to pull it out properly. I would rather be pulling large weeds or pruning. Grass is difficult to eradicate once it gets established in the crowns of perennials and ground cover beds. One option is to start pulling out the grass now and continue paying close attention to these infested areas over the course of the growing season this year and next year. The best time to do this is when the soil is moist, as it is easier to get the roots out. The more roots you remove, the faster you will get rid of the grass. It is important to prevent the grass from setting seed and spreading further throughout your garden beds. If you do not have time to weed out the grass that has gone to seed, just carefully cut off the seedheads and discard them. Be careful if you are seeding any adjacent areas in the lawn so that the seed does not drift into any beds. A breeze can blow the lightweight seed into undesirable areas. Weeding grass out of beds will take a good deal of patience and persistence to be successful. In time, the grass should weaken and eventually disappear as you continually weed it out. A weeding tool with a forked end and a trowel are good tools to use to get more of the roots out.
You may need to lift some of your perennials, divide them and carefully remove the grass before replanting the clumps of perennials. This is a good way to renovate the border and eradicate the grass. This will not work with most ground covers, however, so you will need to weed out the grass in these areas.
There are herbicides such as Ornamec that selectively kill grasses growing in beds of ornamental plants including perennials, ground covers and shrubs. Spray these products over the ornamentals to kill the grass. The herbicides are systemic and will kill the grass roots. Be sure to read the label to determine if it can be used safely with the plants in your garden. If a plant is not specifically listed on the label of Ornamec or on the product that you choose, test it first on a small section to make sure it will not kill or damage your ornamental plants. The best time to apply this product is when the grass is actively growing in spring and fall. It will not work as well in the heat of summer when grass growth slows.
A non-selective herbicide is not ideal in these situations due to the proximity of ornamental plants. A non-selective herbicide such as glyphosate will kill the grass as well as the ornamental plants. To control grass growing within your perennials and ground cover beds, put on rubber gloves first and then a cheap cotton glove on top. Using two fingers on the cotton glove, dip into the herbicide and carefully wipe the blades of grass, avoiding any drips. This method is good for small-scale eradication of very difficult-to-control grasses such as reed canary grass.
It is very important to read and follow all instructions on labels.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at [email protected]. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.