Company 3 responded to a report of a lawn mower on fire behind a residence with grass and leaves burning out of control around it on Woodside Drive. Upon arrival, found a lawn mower fully involved and leaves burning around it. Extinguished using a PW Extinguisher, 100 x 1″ hose and 500 gallons of water. The cause of the fire was combustible materials too close to the engine exhaust.