Used motor oil is not an effective fertilizer. Not only will dumping used motor oil on your grass hurt your lawn, but you'll also pollute the water supply. Instead, use a chemical or organic fertilizer on your lawn or garden.
Motor Oil Pollution
Motor oil is a sticky, insoluble substance that degrades slowly and sometimes contains toxic chemicals. Dumping the used motor oil from one oil change on the ground or down a drain pollutes a million gallons of fresh water, according to the U.S. Environmental Protection Agency.
Recycling Motor Oil
Recycle your used motor oil instead of dumping it on the ground. Store used motor oil in a clean plastic container and take it to a service station or recycling facility. These facilities clean the oil and recycle it into new motor oil or other petroleum products.
Fertilize your lawn or garden with chemical fertilizers, which typically contain a combination of nitrogen, phosphorus and potassium, or organic fertilizers such as composted manure, kelp or blood meal. Always follow manufacturer instructions, because chemical fertilizers also contribute to pollution. Performing a soil test before you fertilize helps you determine how much fertilizer your soil needs.