Can You Use Old Motor Oil To Fertilize Your Lawn?

There’s a seemingly endless number of unconventional ways to fertilize your lawn on a budget. 

At some point, you’ve probably heard of using old motor oil as fertilizer. 

Does this work, and what does motor oil do to grass and other plants? 

Motor oil, new or used, should never be used as fertilizer. It will kill grass, weeds, and any plants it comes in contact with, and it will do long-lasting damage to your lawn. In addition, motor oil is a pollutant, so disposing of it in this way is illegal in many areas.

If you want to know more about this unusual myth as well as what motor oil does to grass and other plants, keep reading. 

Can You Use Old Motor Oil As Fertilizer?

If you’ve ever watched the classic cult film Fight Club, you likely remember the “Did you know you can use old motor oil to fertilize your lawn?” mock EPA billboard lovingly created by Project Mayhem. 

Perhaps this got you wondering about whether or not motor oil is a viable fertilizer.

Interestingly, this film isn’t the only source of this bizarre myth; it’s been perpetuated for decades by a variety of questionable sources, and if you didn’t know any better, you’d probably think this sounds reasonable at first. 

After all, there are plenty of tried and true unconventional ways to use organic fertilizer on your lawn, such as grass clippings, earthworm droppings, and even homemade compost.

Speaking of fertilizer, make sure you know how long to wait after watering your lawn before fertilizing.

Unfortunately, old motor oil is not an effective fertilizer by any means. 

The toxic chemicals in motor oil will seriously damage your grass and other plants and animal life in your yard.

Plus, in many areas, using motor oil as fertilizer is illegal, as the damage done by disposing of motor oil in this way is extremely environmentally unfriendly and long-lasting.

So, if you don’t want a sudden notification and a costly fine from your local environmental agency about the nasty, goopy motor oil all over your lawn slowly seeping into surrounding groundwater, it’s best to find a safer, more responsible (and legal!) way to dispose of it.

What Does Motor Oil Do To Grass?

Motor oil comprises crude oil and a wide range of additives designed to keep your engine running properly and prevent rust, minimize foaming, and reduce friction.

These additives are great for your car’s engine, but they certainly aren’t meant to be applied to plants. 

Many of those additive ingredients are also major environmental pollutants, meaning they are damaging to natural life, such as the grasses and plants in your lawn, for example.

Used motor oil is even more damaging, as it is usually heavily contaminated by tiny bits of metal, dirt, and other chemicals it manages to collect. 

At the same time, it ran through and protected your car’s engine. 

These contaminants will not break down when applied to your lawn; they will collect and prevent anything from growing wherever you apply it.

When motor oil, used or new, is applied to grass or other plants, it kills them quickly and permanently. 

It also looks and smells awful when applied to your lawn.

Motor oil causes harm to plants and eventually kills them by coating them heavily in the viscous oil, contaminants, and other additives, in turn suffocating them and preventing them from absorbing and utilizing the oxygen necessary for their growth. 

In addition, the oil will kill off any soil microbes and invertebrates necessary for plant growth, such as worms and other tiny bugs, which help to aerate the soil and produce vital nutrients for it.

Essentially, motor oil will either damage or outright kill anything natural it touches. 

Plus, as we touched on earlier, it will contaminate your local water table supply, so in most places, it is illegal and extremely irresponsible to dispose of motor oil in this way. 

If you don’t want a hefty fine and a yard full of dead plants, avoid putting motor oil on your lawn and use great care whenever handling and disposing of it to prevent oil spills, such as when changing the oil in your car.

Can Old Motor Oil Be Used As A Weed Killer?

Motor oil certainly will kill weeds permanently if applied to them. 

Still, for the many reasons stated above, it’s best to use a product designed to kill weeds instead, such as Ortho GroundClear, Natural Armor, or even a natural homemade weed killer made of less environmentally harmful ingredients.

Since motor oil is a pollutant, it will contaminate your local water supply by seeping into the groundwater, killing off any other plants it touches (including plants you want to keep!), and preventing anything from growing back for many months or more, even years. 

Avoid applying it to your lawn for any reason, even in small amounts, to kill off a few pesky weeds.

Additionally, motor oil is harmful and toxic to animal life, such as the birds and squirrels who likely frequent your yard. 

The motor oil will contaminate their water and food supply (such as the worms, flowers, and nuts in your yard) as well as hurt their sensitive skin.

How To Properly Dispose of Old Motor Oil

If you’re simply looking for a quick and easy way to dispose of some old motor oil left over after changing it in your car, you’ll most likely need to get in touch with a recycling center or service station. 

Because it is extremely harmful to plant and animal life and doesn’t break down easily, you won’t be able to just dump the oil in your yard or trash. 

Put the oil into an empty oil container and carefully transport it to a recycling center near you. 

If you aren’t sure where one is located, there are convenient services such as Earth911.com, which will direct you to the nearest one if you provide your zip code. 

You also have the option of calling a local service center to inquire about the best place to dispose of used oil.

Additionally, be sure to dispose of any old oil filters properly as well. 

These will need to be drained and recycled by a designated recycling center.