Many clients contact the Extension office frustrated with grasses taking over flower beds or vegetable gardens. A common phone call might involve Bermudagrass taking over a bed of juniper groundcovers or daylilies. If you’ve ever tried to pull Bermudagrass out by hand, you’ll quickly learn that it just grows right back from any root fragments left in the soil. It’s nearly impossible to dig or pull out every piece of Bermudagrass by hand.
One option to control grasses in flower beds is what I like to call the “smothered and covered” method. Mulching can be used to effectively control small infestations or in areas where herbicides cannot be used. Cover the entire infestation with several inches of mulch. This may include wood chips, pine straw, or similar materials. Hay and grass clippings should not be used as mulch since these may potentially carry weed seeds. Covering the area with a layer of cardboard topped with mulch may improve the effectiveness of this method. The mulch should stay in place for at least two growing seasons to kill tough perennial grasses.
Depending on whether these weedy grasses occur in a flower bed or a vegetable garden, you may have certain options to control weeds with selective herbicides labeled for one situation or the other. In vegetable gardens, you can use an herbicide containing the active ingredient sethoxydim (brands such as Poast and Vantage) around broadleaf vegetables to control bermudagrass, crabgrass, and other grasses without harming your veggies. This product cannot be used around corn, since corn is in the grass family and will be damaged by this product. This chemical is very selective for controlling grasses and will not control other weeds.
For flower beds, there are also product options on the market that can be used to selectively control weedy grasses. Products containing the active ingredient clethodim (Envoy), fluazifop-p (Grass-B-Gon and other brands) or sethoxydim (Segment) are safe around most flowers and shrubs. For nutsedge invading flower beds, there is also a selective product that contains imazaquin (Image) that can be applied over the top of several ornamentals. Be sure to read the label for which plants are safe to spray around.
You can also use a non-selective herbicide containing glyphosate (brands such as Roundup and others) in between rows and along borders of vegetable gardens and flower beds. However, because this is a non-selective herbicide, you must avoid any direct contact or spray drift with desirable plants. Do not spray on a windy day. You can also make a “shielded spray” application by using a piece of cardboard or other barrier to shield your plants and spray just the weeds. As long as the spray does not contact the leaves of your vegetables, fruit trees, shrubs, or flowers, then it should not cause damage to these plants.
Glyphosate is inactive in the soil, so you don’t have to worry about it affecting plant roots in the areas that are treated. Make sure the formulation you buy only has glyphosate in the active ingredient. Many other herbicides and combination products are soil active and will not be appropriate to use in these situations. For example, avoid using combination products such as “Roundup Extended Control” which should never be used in a vegetable garden or flower bed.
One last tool to add to your weed control toolbox is a pre-emergent herbicide. You may want to consider using pre-emergents in combination with mulch and other selective herbicides, as needed. There are several products on the market such as trifluralin (Preen, Treflan, and other brands) that can be applied to prevent the seeds of annual grasses (i.e. crabgrass) from growing. Pre-emergents will not control any weeds that are currently established, but will significantly reduce the amount of weeds that come back from seed. Timing is the key with pre-emergent herbicides. They should be applied before March 15 for weed prevention in flower beds or incorporated into the soil of a vegetable garden according to the label. Be sure to read and follow all labeled application rates and safety precautions when using herbicides.
Paul Pugliese is the Extension Coordinator and Agricultural & Natural Resources Agent for Bartow County Cooperative Extension, a partnership of The University of Georgia, The U.S. Department of Agriculture, and Bartow County. For more information and free farm, lawn, or garden publications, call (770) 387-5142 or visit our local website at ugaextension.org/bartow.