How to Kill Grass Invading a Flower Bed

Use a Herbicide -- but Pick the Right Kind

Portrait of lovely senior woman taking care of plants
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Gardening is a deeply satisfying hobby -- you do it outside in the sunshine and warm breezes, and since it's usually done solo, it's a time for contemplation or losing yourself in gardening and forgetting about any problems in your life. Then you get a huge bonus: gorgeous flowers and/or delicious vegetables as the fruits of your labor.

But green grass, so lovely in the lawn, is definitely an invader in a garden so lovingly tended, as are weed-like grasses like crabgrass and other varieties.

It's a problem for most gardeners to kill the grass without hurting the flowers as collateral damage. Regardless of whether the flowering plants are perennials or annuals, this is an issue.

Digging or pulling up the grass is a huge task and generally not feasible. A herbicide is the best answer. 

Using Herbicide in a Flower Bed

You have several choices regarding which kind of herbicide to use to kill grass in a garden area.

One choice is to use a broad-spectrum herbicide. It will kill any ornamental plant it comes into contact with, as well as grass and weeds. It will also kill any lawn grass it comes into contact with. If the grass is close to but not touching your garden flowers, you can place a cardboard shield between the garden plants and the invading grass and use a broad-spectrum herbicide on the grass. Do this on a calm day to prevent herbicide drift from damaging your flowers. For any garden plants that are still small, you can protect them with a bucket or large flowerpot.

If you need to kill grass growing close to ornamental plants, you can apply a selective herbicide that targets only grasses without harming your garden plants. These herbicides will kill most annual grasses like crabgrass and foxtails, as well as perennial grasses like nimblewill and quackgrass.

If you have perennial nutsedge, also commonly called nutgrass, you need to apply a herbicide specifically labeled to kill nutsedge.

You can identify nutsedge by the small tubers in the root ball. Nutsedge isn’t a grass but rather is a member of the sedge family.

You can kill broadleaf weeds that invade your garden in the same way as grasses. If you find you have certain weeds or grasses returning year after year in the same location, they are perennials. You can keep these pests from ever coming up by using a pre-emergent herbicide where you know they will grow several months before they emerge. 

Read the label carefully before you buy any herbicide to be sure it will kill the type of weed or grass that is invading your flower bed and that it is the type you want, whether broad-spectrum or selective or pre- or post-emergent.

Once you achieve control with a herbicide, prevent the grass from coming back by following these procedures:

  • Cover the soil of the flower bed with a 3-inch layer of mulch to discourage new grass seeds from germinating.
  • Apply a corn meal gluten-based product to prevent grass and other weed seeds from germinating. This also prevents flower seeds from germinating, so apply after your flowering plants germinate.