The purpose of the flight was to provide instrument training to a non-instrument rated pilot. The aircrew estimated that there was 10 gallons of fuel on board when they took off. About 1 hour later, the engine lost power as the aircrew were entering the traffic pattern to land. Reportedly, the right fuel gauge indicated empty, but the left gauge indicated about 1/4 full. The instructor pilot took control of the aircraft, but was unable to restart the engine or glide to the airport. A forced landing was made in a field of potted trees at a nursery. During touchdown, the landing gear struck a number of 5 gallon cans in which the trees were potted and the aircraft nosed over. Less than 1/2 cup of fuel was found in the fuel tanks after the accident. The aircraft had been flown 2.1 hours on the previous flight. The aircrew estimated that the plane would fly 3.3 to 3.5 hours without refueling. The total time since the plane was refueled was about 3.1 hours.