Mowing the lawn always produces piles of waste grass, especially if you mow infrequently. If you don't have a compost pile or an out-of-the-way place to let the grass decompose, one disposal option may be to burn it, as long as you live in a community that allows burning. If the grass is green, however, it is full of moisture and will smolder and burn inefficiently if you simply try to ignite a pile of it. The best way to burn it is to add it incrementally to a fire that is already burning well.
Clear a space in your yard about 5 feet in diameter for a fire pit, and surround it with rocks. The pit should be 50 feet from any buildings and have clear overhead access, with no overhanging trees or wires.
Form a pyramid with three or four logs in the center of the pit, then crumple up some newspaper and place it in the center of the pit. Stack kindling wood or small branches on top of the newspaper, taking care not to disturb the logs, and leave an access so you can light the newspaper.
Pour a small amount of fire starter on the kindling, then light the newspaper with a lighter. Stand back and let the fire burn until the logs ignite.
Start throwing the grass in handfuls onto the fire after it is hot enough to ignite the logs. Spread it around the fire, and be sure a handful has burned completely before you throw another one on top of it. Be patient. If you add too much grass at once, it will begin smoldering and will inhibit combustion of the wood.
Stir the fire periodically with a shovel to disperse partially burned grass and mix it in with the burning wood. Add more logs as necessary to keep the fire hot.
Let the fire burn itself out when all the grass has been burned. Stay with the fire as long as there are flames. When only embers remain, either cordon off the fire pit and leave it overnight, if it safe to do so, or soak the fire with water from a garden hose, turning it with a shovel as you soak to be sure all the embers go out. Letting the fire burn overnight will reduce all the embers to ash and make the cleanup easier.