Kentucky bluegrass is a great choice for a healthy lawn, but you may want to use the space for something other than lawn. Several methods exist to get rid of Kentucky bluegrass, with some taking more time and labor than others. Choose the method that best suits your purposes and resources.
Spray Kentucky Bluegrass with an herbicide such as glyphosate, which will not leave harmful residue in the soil that can then leach into the water supply. For best results, spray it in the morning on a sunny day when there is no threat of rain. This method will kill everything and leave a layer of dead plants you can either work into the soil or rake up.
Pull the grass up by cutting it with a sod cutter, then rolling it up. You can use it somewhere else in your lawn or compost it. This method provides almost instant results but requires more labor. You can rent a sod cutter from a local hardware store.
Mulch your Kentucky Bluegrass lawn. Mow the lawn short, then laysheets of paper or cardboard over the area you wish to remove. Place a few inches of mulch or compost down immediately to keep the paper from blowing away. Water the area well so the paper gets soaked. You can garden right over this or wait about a month to six weeks for the underlying lawn to die.
Burn off the Kentucky Bluegrass by laying a sheet of black plastic over the area you wish to clear. Hold it down with rocks along the edges to keep the wind from lifting it. This will take six to eight weeks to kill off the hardy grass plants, so start in early spring before the growing season gets under way. Remove the plastic and rake up the dead grass.