Oil in soil: contamination risk


Recently, a car crashed into our front garden and spilled its motor oil in the flower bed. The soil is frozen now, but I’m concerned about the oil seeping into the soil during spring thaw and the effects this will have on surrounding plants (trees, shrubs and perennials). Is there anything I can do to protect existing plants?


Dear Writer,

Thank you for writing about your unfortunate situation. Your concerns, and instincts, are absolutely correct, and hopefully we can help with suggestions for your specific course of action.

And for yourself, and for all our readers, we’re posting this information first:

*  If you see a spill, and even if you’re not responsible, you should still report it to the Ministry of the Environment’s Spills Action Centre on 1-800-268-6060 (toll free/24 hrs).

*  For detailed instructions, visit the Ontario Ministry of the Environment at  https://www.ontario.ca/environment-and-energy/report-spill

Heavy metals and organic minerals such as carbon, potassium, magnesium, iron, zinc and cobalt are all present at high amounts in used engine oil. Even though some of these minerals are actually present in healthy soil, a significant saturation by spent oil will cause die-off of microbial life in the soil. This can overdose plant life, cause growth disorders, and even failure to germinate. Because this oil is heavy, and sticky, and contains an extensive concentrated cocktail of toxic compounds, it can build up, and persist in the environment for years.

Unfortunately, most soil organisms immediately exposed to the oil will perish. Oil coats their bodies and smothers them. Oil has a tendency to hang around for a very, very long time. It’s likely impossible to determine how old the engine oil was that spilled on your garden.  But when used engine oil is dropped into the soil, it not only kills off microbial life, but can also make the soil impassible for worms and other small organisms. Soil polluted in this way is unsuitable for any growth, and very large contaminated areas have taken years, and specialized treatment, to recover fertility.

Questions for you might be: How much oil actually spilled? And before the frost set in, were you able to remove any of the oil, or the soil/plants/grasses that it coated ? You mention that you have shrubs, trees and perennials. Depending on the proximity of the root systems, you really want to assess how much plant material and soil to safely remove, how to safely dispose of the contaminant, and how to amend the area with clean compost and soil. 

To find a landscaping professional to help you with garden planning, visit Landscape Ontario. Their site contains excellent gardening information as well as lists of member companies providing services in landscape design, construction and maintenance, as well as a variety of specialists.  https://www.landscapeontario.com

Also, with the advice and assistance of the Spills Action Centre, hopefully you will be able to work on a solid plan for restoring your front garden. And we also hope that all our readers will benefit from your difficult experience.

Again, you can report your spill by calling:

  • 1-800-268-6060 (toll-free, province-wide, 24/7)
  • 416-325-3000 (Toronto area)
  • 1-855-889-5775 (TTY)


You might find this website from the Cornell Waste Management institute helpful:  https://cwmi.css.cornell.edu/sourcesandimpacts.pdf