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Tips for battling Bermuda grass

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BERMUDA GRASS IS THE BANE OF A GARDENER’S EXISTENCE. It is a warm season grass, and in our climate, actively grows during the mid-spring and summer season. It is dormant in winter and looks dead. Don’t be fooled. Creeping through the soil, or along the surface, thick distinctive yellow roots or above-ground shoots called rhizomes crawl and spread in every direction.

Bermuda grass can grow a couple of feet a year. It is often found in lawns, and from there — if not controlled — spreads into flower beds where it threads its way through other plant’s roots, effectively making the grass impossible to remove without digging up and removing plants it has become intertwined with.

Bermuda grass propagates both vegetatively from rhizomes and also from seed, but the rhizomes are by far the fastest and most effective way it reproduces. If soil is rototilled, each tiny piece can root and grow. If you dig it out, each piece left behind will grow. There are, however, various ways to control and remove Bermuda grass. Some require time and patience, others painstaking digging and weeding. Some opt for spraying it with herbicides. You can minimize its presence in your lawns by using specific lawn care practices.

Bermuda grass is an introduced grass probably originating from tropical Africa, not from Bermuda. It very likely came in as seeds in contaminated hay, and there are also records of imported Bermuda grass seed in Georgia in the 1700s. Reports of flats of Bermuda grass being sold in San Francisco in 1856 for $5 exist. It has since spread to many states as a weedy plant in gardens and on farms. Worldwide, it is considered one of the most problematic weeds for farm crops in the grass family. Improved hybrid strains of Bermuda grass are used as a turf grass in the southwest. Other strains are used as pasture grasses.

If you have a patch of Bermuda grass in your garden, the time to act is now. Dig it all out before it spreads and becomes a much bigger, more complex problem. If soil is moist, this task is fairly easy although tedious. After you are finished, repeatedly check the area during the growing season. Diligence is necessary to continue to dig out and remove any stray strands that survive your removal efforts. Do this right away before these strands gain strength.

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BERMUDA GRASS IN LAWNS: In our area it thrives in dry infertile soil. In a lawn, it is usually found where lawn grass is weakest due to poor growing conditions such as too-low mowing, inadequate irrigation and poor soil fertility. Many lawns contain all of these conditions. Robust lawn grasses (especially fescues) adequately watered, fertilized and mowed at the highest lawnmower setting can usually out-compete Bermuda grass. If you have Bermuda grass in your lawn, water regularly, fertilize in the appropriate seasons, and very importantly, mow at the highest settings. Bermuda grass should diminish over the course of a season or two. In the fall, seed any weak areas with grass and clover seed. Strawberry clover is an excellent, drought-resistant lawn clover.

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SPRAYING BERMUDA GRASS FOR REMOVAL: Some people are adamantly against spraying herbicides, while others will resort to spraying herbicide to kill Bermuda grass. This column does not recommend this practice in particular - but contains information to minimize the use of herbicide products if you make this choice. Some people say that herbicides don’t kill Bermuda grass, but sprays are effective using specific methods. Spraying Bermuda grass when dormant won’t kill it so don’t spray in winter, early spring or late summer. Wait until the grass is green and actively growing in early or mid-summer, then spray. One application should kill almost all of it. A very small amount of spot re-spraying or digging should take care of any areas that did not get adequate coverage the first time. The Bermuda grass at this point can be safely dug out, removed with a sod cutter, or can be sheet mulched over. “Organic” spray products such as vinegar will only burn the surface growth back and will not affect the vigor of the underground growth parts.

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SHEET MULCHING: It is possible to kill Bermuda grass lawns by sheet mulching — but it takes patience. If you have lawn sprinklers, make sure to mark them with landscape flags to reuse or convert them to drip at a later date. First dig a small trench about 6-8 inches deep around the outside perimeter of the area, making sure to dig below the level of the Bermuda grass. Throw this material either on the lawn or in the green bin so you won’t have a “fringe” of surviving Bermuda grass around the whole area. The small trench will also contain compost from spilling over onto sidewalks. Put two layers of corrugated cardboard over the whole area, making sure cardboard goes to the bottom of the trenches on the perimeters. Overlap each piece by at least 6 inches. Cover it all right away with 6 inches of composted greenwaste. Do not cover them with wood chips because the cardboard and compost will create healthy, fertile soil at the end of the process, and the wood chips will not. When wood chips decompose, nitrogen is removed from the soil. Now comes the patience part. Wait about 1½ years for Bermuda grass to die before planting. You can also use plastic or even old carpet to cover and smother Bermuda grass, but this will not result in healthy, fertile soil at the end of the procedure. Keep in mind the smothering process is effective only when the Bermuda grass is actively growing. That’s why it takes so long.

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BERMUDA GRASS IN VEGETABLE GARDENS: Some homeowners and commercial growers use black plastic over vegetable beds for weed control. Sometimes Bermuda grass is an issue in vegetable gardens. If this is the case, you may want to use black plastic to cover beds and pathways for a couple of years to kill it. A recent garden where this was the case spread compost over the whole area and tilled it in, then placed 6 millimeter thick black plastic over the beds from pathway to pathway, and a permeable plastic over the pathways so water will drain when it rains. Holes were cut for each vegetable plant in the beds. At each planting hole, any pieces or fragments of Bermuda grass rhizomes were assiduously removed from the hole and around the hole. This method will not remove all of the stubborn grass, but it will vastly minimize it and will allow most of the vegetable garden to thrive.

Kate Frey’s column appears every other week in Sonoma Home. Contact Kate at: katebfrey@gmail.com, freygardens.com, Twitter @katebfrey, Instagram @americangardenschool

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