Keeping Bermuda Grass Out

Q. Is there a way to keep Bermuda grass from getting into my flower beds?

A. In order to successfully beat this aggressive grass, you need to be just as aggressive.

One of the usual approaches to preventing grass creep is to install edging, but while it's good at keeping out many grasses, most metal edging — at four inches wide — is too narrow to stop Bermuda grass effectively. If you do want to try that route, heed Gardening by the Yard host Paul James' advice: Sink the edging three inches into the ground, allowing one inch above the soil surface. You will have stopped most of the rhizomes' underground tunneling, but Bermuda grass will also try to creep over the edging, so you'll have to be vigilant about making sure that it doesn't.

An avenue that some gardeners use is simple trenching. The principle is to create a "divide" between your bed and the lawn. It won't stop the Bermuda from trying to enter the garden — it can bridge the gap — but it makes it easy to see and to stop. Dig a vertical four-inch trench around your bed, then angle the edge of your planting area in such a way as to leave a 45-degree angle between the two. While you can do this by hand or an edging tool, a trenching shovel also makes quick work of the digging part of this project. You'll need to be sure to remove every single piece of cut grass, however, that's on the bed side of the divide; the stolons regenerate. Monitor the trench weekly, and pull up any grass that's trying to cross. Refresh the trench every spring.

If your bed is large, monitoring the perimeter will seem like an endless battle. To aid your efforts, try an herbicide along the edge of the trench. In or near the garden bed, you can use a grass-targeting herbicide that contains fluazifop (like Grass-B-Gone). If you live in areas where Bermuda grass grows rampantly, you'll need to do repeat applications, probably every two weeks.

The other choice would be a glyphosate-based herbicide (like Roundup), but you'll need to be very careful to spray only the perimeter of the bed. Glyphosate acts as a systemic, meaning the plant absorbs the chemicals and distributes them throughout the plant, including the roots. The glyphosate will kill any other plants it touches. Continue applying as any new Bermuda grass growth appears.

Maintenance tips: Mow around the beds from left to right — with the mower blower facing away from the bed — so that no grass clippings are sprayed into the bed. Any stray pieces of Bermuda grass will easily root in the bed. Then, instead of using a trimmer-edger to finish it up, do the trimming by hand.

You may or may not want to tackle the source of the grass — the lawn or a weedy area in the driveway. If you do, fall is a great time to take it on, using a glyphosate product. Then reseed. You may find you'll need to keep up treatments for a few years before the Bermuda grass is gone.