Let it grow.
Credit: Kyu Oh / Getty Images

According to the EPA, using a catalytic converter–free gas mower for one hour is equivalent to driving 11 cars for an hour, whereas mechanical push mowers are energy- and emissions-free. Besides, the ideal length for cut grass is actually about 2-1/2 to 3-1/2 inches. Taller blades have deeper roots, which are able to find water more easily during long periods without rain or watering. We like Brill's RazorCut Premium 38 lawn mower ($176).