For the best aesthetic, we recommend killing your existing turf grass. Whether you have Kentucky Blue Grass, Tall Fescue, Bermuda grass, Saint Augustine, Perennial Rye or some other thirsty grass, you will receive best results if you first kill the existing turf grass. Although we always prefer natural lawn and garden products, the most efficient means would be to use a chemical like Glyphosate (Various brand names exist. Check with your local garden center or hardware store). These chemicals only work on grass that is actively growing (not dormant). Which means you must water the existing lawn to ensure there is no dormant grass, otherwise if you don't, it will be lying in wait until conditions are ideal, such as after planting when you are soaking the ground regularly.
You are more than welcome to plant in your existing turf, which is definitely the easiest route but also the least aesthetically appealing.
If not opposed to glyphosate, make sure your existing turf is not dormant and actively growing by giving some good waterings prior to spraying. (IF it is heat dormant you will need to spend a good week or two watering to ensure there is ample leaf surface to absorb the glyphosate.) It is many times easier to kill your existing turf prior to planting than after. If you are confident that there is no dormant roots then one application will do, but to be 100% confident give yourself enough time prior to planting Dog Tuff ™ grass (with waterings) to be sure no grass is going to reemerge after planting. If you see some grasses reemerging, then spot spray.
For those of us who are not comfortable with glyphosate; if you think of it as a 1 time application of chemicals to bring your yard to a water-wise standing it is a little easier of a pill to swallow.
Applying a pre-emergent after the glyphosate application will make the process much easier. This will aid in the period prior to planting but through the process of planting and the neccesary disruption to the soil it will be rendered inactive; therefore we reccomend an application after planting. But this can be avoided if you have many hands to aid in manual weed removal. (This is no small task..)
Kill the old lawn at least 2 weeks before the Dog Tuff ™ grass plugs arrive. If you don’t kill the old grass, it will compete with the Dog Tuff ™ and look unattractive. The ground should be deeply irrigated for a few days before installing the Dog Tuff ™. Alternatively, if you will be planting Dog Tuff ™ in bare, freshly cultivated soil there are some different steps. In this case, plant the plugs in damp soil, apply an organic lawn food (has lower nitrogen), apply a pre-emergent weed preventer chemical, then irrigate frequently to maximize growth.