Nature’s notebook

You can see ozone’s effects in your own garden

Bee on a yellow cutleaf coneflower, in the author's garden. Photo: Ruth Ann Grissom

The ozone that occurs naturally in the upper atmosphere protects us from the sun’s burning rays, but the ozone produced at ground level damages our lungs. It is created when sunlight mixes with emissions from automobiles, industries and coal-fired power plants. Ozone pollution is the haze we see on hot summer days, although in the Piedmont Carolinas, the season extends from March to October.

In healthy individuals, ozone pollution might cause a tight sensation in the chest or mild shortness of breath, but it can be deadly for those with heart or lung disease – an elder with emphysema or COPD or a kid with asthma or chronic bronchitis. Children are especially vulnerable to long-term damage from ground-level ozone because their tender lungs are still developing. To make matters worse, they typically have greater exposure to air pollution than adults since they spend more time outdoors engaged in vigorous activities.           

Some plants are also more sensitive to ground-level ozone than others. Exposure causes a distinctive pattern of black or purple dots, called stippling, on the upper side of leaves. The discoloration can be distinguished from insect damage and other factors because it does not cross the veins or affect the backside of the leaf. Many plants are ozone-sensitive – ranging from the snap beans in our gardens to the tulip poplars in our forests. I’ve noticed a similar stippling on the brown-eyed Susans (Rudbeckia triloba) I’ve grown from seed collected in the Uwharries. 

The cutleaf coneflower (Rudbeckia laciniata) is a popular bioindicator of ozone damage. This rugged native benefits a range of pollinators and performs well in almost any sunny spot.  Reaching a height of up to 5 feet, it produces cheerful yellow flowers from summer to fall. Since the stippling is worse on older leaves, the ones more visible near the top tend to stay fresh and attractive.

For the past several years, Clean Air Carolina has led an effort to install ozone gardens in a variety of settings across Charlotte, from parks and greenways to the Carolina Raptor Center to the Belk Corporate Campus. This lets people monitor the cumulative effects of ozone over the course of the season, providing a visual reference for the damage inflicted on our lungs.

The group has also targeted area schools. These gardens offer an obvious scientific learning opportunity for students, but what better place to draw attention to the dangers of air pollution than having ozone-sensitive plants in proximity to the typical carpool line? Clean Air Carolina encourages parents not to idle more than 30 seconds in school parking lots, noting that it’s actually more fuel efficient to turn off the engine and restart it than to idle for only 10 seconds.

In June, I attended one of Clean Air Carolina’s ozone-garden workshops at Wing Haven in Charlotte. After the lecture portion, we walked to the garden established on the Little Sugar Creek Greenway in 2012 to observe established plants firsthand. At that point in the season, the plants hadn’t suffered any damage. Participants left with a cutleaf coneflower to plant in their own gardens. I tucked mine into the back of a bed near other tall natives such as Joe Pye weed, ironweed and hibiscus. Thus far, it’s showing little damage, but that could be due in part to the drought we’ve suffered this summer. When plants close their stomata to conserve moisture, they absorb less air pollution.

That said, air quality has improved in Charlotte since I first moved here in 1995. Even though there are now more cars on the roads, they’re generally cleaner and more fuel-efficient. In 2002, the N.C. legislature passed the Clean Smokestacks Act to reduce emissions from the state’s coal-fired power plants. Later that decade, then-N.C. Attorney General Roy Cooper sued the Tennessee Valley Authority, forcing it to clean up its facilities, whose emissions were wafting over the mountains and contributing to our poor air quality.

I’d like to plant another cutleaf coneflower in the Uwharries, where the only official ozone monitor is in Candor. Ground-level ozone tends to be worse in urban areas with heavy traffic, but as noted above in the TVA case, air pollution doesn’t recognize geo-political boundaries. Much has been made of the rural-urban divide, but this is an example of the connection. The entire Piedmont, including rural areas like the Uwharries, is prone to ozone pollution due to our geography. According to Calvin Cupini with Clean Air Carolina, “The topography of the Piedmont, especially the slow slide downward to the coast, allows for ozone formation.”

To see this in action, review the EPA’s archival ozone maps. I focused my search on the Uwharries (using zip code 27371) then zoomed out to view the entire Piedmont. I clicked through a couple of weeks in mid-July when the weather was especially hot and dry. It’s mesmerizing to watch the blobs of green, yellow and orange shift around the region from day to day. As these maps illustrate, we’re all in this together.

At this point, we’re in the closing days of ozone season, but you can prepare for next spring by planting a cutleaf coneflower and signing up to receive daily ozone forecasts at

Learn more about air quality at the website.