subscribe
YouTube
Pinterest
Twitter
Facebook
Instagram
Search

Does Excess Car Exhaust Damage Gardens?

By: Jessie Keith

“How would a parking lot with 16 stalls [and the car exhaust] next to my garden interfere with plant photosynthesis?” Sylvia of Belle Plaine, Minnesota

Answer: It is a very interesting question. Car exhaust contains gasses that are helpful to plants and photosynthesis and some that are harmful. Car exhaust is also everywhere, especially if you live in an urban area, though the increase in hybrid and electric cars is reducing car fumes. Still, nearby fumes may have some impact. Here is a breakdown of exhaust components from a standard car that runs on gasoline followed by the potential impacts of those gasses on plants and photosynthesis.

U.S. Environmental Protection Agency estimates of average passenger car emissions in the United States for April 2000
Component Emission Rate Annual pollution emitted
Hydrocarbons 2.80 grams/mile (1.75 g/km) 77.1 pounds (35.0 kg)
Carbon monoxide 20.9 grams/mile (13.06 g/km) 575 pounds (261 kg)
NOx 1.39 grams/mile (0.87 g/km) 38.2 pounds (17.3 kg)
Carbon dioxide – greenhouse gas 415 grams/mile (258 g/km) 11,450 pounds (5,190 kg)

(Click here for more exhaust gas details from Wikipedia.)

Carbon Dioxide and Plants

Here is the equation for photosynthesis as defined in Brittanica: 6CO2 + 6H2O → C6H12O6 + 6O2. Carbon dioxide is essential for photosynthesis, which is why it’s good to plant as many trees and garden plants as you can to help reduce this most abundant greenhouse gas. Plants take CO2 out of the atmosphere! Trees and large plants are highly effective photosynthesizers due to their sheer size, and grasses are super photosynthesizers, so consider planting a row of ornamental grasses (click here for some great ornamental grass options) or some trees and shrubs nearby to combat local CO2.

Carbon Monoxide and Plants

I found a technical overview of carbon monoxide in the atmosphere, which stated: “Carbon monoxide does not poison plants since it rapidly oxidizes to form carbon dioxide which is used for photosynthesis.” So, it is not harmful to plants either.

Nitrogen Oxides and Plants

Nitrogen oxides (NOx) contribute to smog, which blocks the sun’s rays, and acid rain, which is harmful to plants, so in excess, NOx is harmful to plants. Still, there is so much NOx in urban areas, the amount produced by the cars in the parking lot next to you would be negligible. On the plus side, you can plant nitrogen-fixing plants, such as plants in the pea and bean family as well as bayberry shrubs, to help with local NOx. These plants actively remove atmospheric NOx and convert it into a soil-borne form of nitrogen that benefits plants.

Hydrocarbons and Plants

In general, petroleum hydrocarbons are toxic to plants in high quantities, especially if they make their way into the soil (oil- or gasoline-contaminated soils). The cars nearby do emit hydrocarbons but in much lower quantities, so they should not be a problem for your garden.

As stated earlier, I recommend planting a tree, shrub, or ornamental grass buffer between your garden and the parking lot. Tough nitrogen-fixing options would be ideal! In addition to bayberry, try the following options suggested by my colleague Russell Stafford: “Outstanding legumes for perennial borders include false indigo (Baptisia spp.), wild senna (Senna spp.), yellow lupine (Thermopsis spp.), lupine (Lupinus spp.), and leadplant (Amorpha spp.).  The roster of leguminous shrubs is also lengthy, boasting such standouts as bush clover (Lespedeza spp.)…” (Click here to read the full article.)

For general greenhouse gas information, I also recommend that you read this informative piece from the EPA about greenhouse gasses and their management (click here to read it).

I hope that this information is helpful!

Happy gardening,

Jessie Keith

Black Gold Horticulturist

About Jessie Keith


Plants are the lens Jessie views the world through because they’re all-sustaining. (“They feed, clothe, house and heal us. They produce the air we breathe and even make us smell pretty.”) She’s a garden writer and photographer with degrees in both horticulture and plant biology from Purdue and Michigan State Universities. Her degrees were bolstered by internships at Longwood Gardens and the American Horticultural Society. She has since worked for many horticultural institutions and companies and now manages communications for Sun Gro Horticulture, the parent company of Black Gold. Her joy is sharing all things green and lovely with her two daughters.

Leave a Reply

Content Disclaimer:

This site may contain content (including images and articles) as well as advice, opinions and statements presented by third parties. Sun Gro does not review these materials for accuracy or reliability and does not endorse the advice, opinions, or statements that may be contained in them. Sun Gro also does not review the materials to determine if they infringe the copyright or other rights of others. These materials are available only for informational purposes and are presented “as is” without warranty of any kind, express or implied, including without limitation warranties of merchantability, fitness for a particular purpose, and non-infringement. Reliance upon any such opinion, advice, statement or other information is at your own risk. In no event shall Sun Gro Horticulture Distribution, Inc. or any of its affiliates be liable to you for any inaccuracy, error, omission, fact, infringement and the like, resulting from your use of these materials, regardless of cause, or for any damages resulting there from.

While we have made every effort to ensure the information on this website is reliable, Sun Gro Horticulture is not responsible for any errors or omissions, or for the results obtained from the use of this information. All information in this site is provided “as is”, with no guarantee of completeness, accuracy, timeliness or of the results obtained from the use of this information.

Use of this site is subject to express terms of use. By using this site, you agree to our Terms of Use

View Our Privacy Policy