Preparing the bed is an important step in the planting process. Your first consideration will be to remove vegetation currently growing in your area. Techniques for this activity are: sun solarization, chemical treatment, or the old fashioned method of digging them up. Each has some benefits and disadvantages.
Sun solarization traps radiant heat energy from the sun and causes the soil temperatures to rise as high as 140º during hot summer months. This can only be done during summer, and is lethal to many bacteria, fungi, nematodes and weed seeds. Clean the surface of the bed, rake it smooth, and dig a trench six to eight inches deep all around the bed. Water to saturate the soil then lay black plastic sheeting over the area, overlapping the trench on all sides. Using black plastic as opposed to clear is recommended because it blocks the sunlight and facilitates higher temperatures. Fill in the trench, weighing down the plastic while pulling it as tight as possible. This method can take as little as two weeks or as long as four to six weeks depending on intensity of the sunlight. It uses no chemical control and is effective, but can only be done during summer.
Glyphosate, (marketed under the names Round Up, Accord and other brands) is a non-selective, foliar-active herbicide. Most plants, when contacted by this spray, will be killed if it is properly applied when plants are actively growing. This chemical is not effective in cool seasons or on dormant vegetation. Bermudagrass with its deep rhizomes is one of the most difficult plants to kill, but the product (glyphosate) may kill even the root a couple of weeks after application. Some tough plants may require more than one application. Two weeks after application the chemical is no longer effective and new plants may be planted without risk of harm from the chemical. Be careful not to use glyphosate in wet or windy conditions that might cause inadvertent spreading of the herbicide.
Glyphosate will damage upper portion of nutsedge, but will not kill the nutlet. A selective herbicide is necessary for this particular plant. As with all chemicals, check the label for directions and recommendations. The herbicide for nutsedge is not guaranteed to be 100% effective.
Hand removal of grass and weeds from a new bed will most probably not be 100% effective. It is almost impossible to remove all roots, rhizomes, and seeds, especially Bermudagrass rhizomes. Depending on actual vegetation in your bed, using a combination of removal methods should provide the best results. The continuing control of weeds or unwanted grass will depend on how well you mulch and maintain your bed. A thick layer of biodegradable newspaper (at least eight sheets thick) covered with mulch can be used to suppress unwanted vegetation. This technique is not as effective on Bermudagrass or nutsedge as chemical applications, but your plants are not at risk from the chemicals.