ARMN Ozone Bio-indicator Garden: Report From the 2022 Growing Season

Photo of a volunteer standing to the left of the Ozone Bioindicator Garden

by Leslie Cameron

The ozone bio-indicator garden at the Walter Reed Community Center (WRCC) is concluding its second full growing season. Arlington Regional Master Naturalists installed the garden in 2020 and are collecting data on the impact of tropospheric or ground level-ozone air pollution on plants, in cooperation with NASA, the Harvard Smithsonian Center for Astrophysics Science Education, and Arlington County. The garden is part of the international Ozone Bioindicator Garden Network, organized in part by the National Center for Atmospheric Research (NCAR) in Boulder, CO. There are 17 ozone gardens across 12 states. Data on the impact of ozone on plants from this garden are uploaded and merged with data from other gardens in the network. 

After its launch into space, anticipated in January 2023, an instrument called TEMPO (Tropospheric Emissions: Monitoring Pollution) will begin taking measurements of major air pollutants, including ozone, across North America. Data from the network gardens will be coordinated with air pollution data from TEMPO. For more background on this project, see earlier blog articles about the mission and installation of the garden (February 2021), and a report on the first full growing season in 2021 (November 2021). 

In 2022, ARMN members Barbara Hoffheins, Todd Minners, Jon Bell, Anne Doll, and Ruth Lane planted, maintained, and monitored the plants for ozone damage.

Other goals were to create signs with a QR code for more information and signs in English and Spanish to educate visitors about air pollution in Arlington and how to reduce ozone levels. 

Photo of a sign that says Ozone Bioindicator Gardne with logos from the Smithsonian, NASA, and ARMN
The QR code on the garden sign links visitors to more information about the project. Photo by Leslie Cameron.

The Smithsonian Astro Observatory supplies all the seeds for this garden. The 2022 garden includes the same varieties of sensitive and tolerant snap beans, sensitive and tolerant tobacco, sensitive potato, and sensitive Common Milkweed (Asclepias syriaca) as were in the 2021 garden. Sensitive Cutleaf Coneflower (Rudbeckia lacianata) was seeded in fall 2021 and added to the garden for the 2022 growing season.

Photo of a volunteer standing to the left of the Ozone Bio
ARMN member Barbara Hoffheins takes a break from working at the garden. Photo by Jon Bell in May 2022.
Photo of a volunteer pointing to a milkweed plant in the garden bed.
This bed includes sensitive beans on the right and tolerant beans on the left in the rear, and milkweed in front. Photo by Jon Bell in May 2022.
Photo of a garden bed with a sign in front
This bed includes sensitive potatoes on the right and tolerant potatoes on the left. Photo by Jon Bell in May 2022.

Ozone causes stippling or purpling on the top sides of leaves (usually not undersides), and inside, not crossing the veins, and it usually affects older leaves (not younger).  Damage from other causes may look like ozone. The first photo (below) shows what ozone damage looks like. The second photo shows damage that is not from ozone. 

Ground-level ozone is more likely to reach unhealthy levels on hot sunny days, and ozone damage to plants is more likely in late summer. In this garden, ozone damage is likely to be more noticeable on second- and third-year perennials. 

Beginning in March, garden volunteers regularly tracked planting, watering, weeding, and other maintenance completed, as well as weather (via NOAA observations for Washington/Reagan National Airport) and ozone levels (via the Virginia Department of Environmental Quality). No damage to plants from ground-level ozone was observed in 2022. These observations were confirmed by outside experts from Howard University and NCAR. The data from these observations will be uploaded to the Ozone Bioindicator Garden Network database in the fall.

Graph which shows Ozone Expsoure Trends in Aurora Hills from M
Ozone trends between May 1, and July 20, 2022, at the Aurora Hills sensor. An NCAR expert confirmed that the levels of ozone from the Aurora Hills sensor did not appear to be high enough or of long enough duration to cause damage. Neither the air monitoring station nor the garden is located near heavy transportation exhaust, which is the leading cause of air pollution in our area.

Readings were also compared to a ground-level ozone sensor in the Arlington’s Aurora Hills neighborhood. Ozone levels vary from area to area and ozone can be blown around by the wind, so a sensor in a nearby area like Aurora Hills will not necessarily measure the same level of ozone as at the garden at the Walter Reed Community Center, about a mile away. However, a reading nearby may be a useful guide. The NCAR expert said that the reported levels of ozone from the Aurora Hills sensor did not appear to be high enough or of long enough duration to cause damage. For more on identifying ozone damage, see

Other takeaways from the garden in 2022:  Based on recommendations from a Howard University atmospheric science professor, the 2022 garden was partially replanted more sparsely to make cataloguing damage easier. The ARMN members maintaining the garden grappled with damage from the usual garden pests—rabbits and possibly other mammals. This will likely remain a challenge in 2023. Seed potatoes saved from 2021 were used to plant in 2022, and this year’s crop is large enough to share with other network gardens as this potato variety is not sold commercially and it is highly valued for ozone research. An idea for next year would be to ask the Aurora Hills community garden staff if they would be willing to plant tolerant and sensitive snap beans and potatoes in their garden to compare with the plants in the WRCC garden. These plants have been good producers, taste good, and they could serve two purposes—one for science and the other for food production.

Reducing air pollution and keeping the air cleaner will benefit all of us. For tips on steps we can take, see AirNow.  

The Ozone Bio-indicator Garden is located at the Walter Reed Community Center (2909 16th St. S., Arlington, VA), in front of the building on the west side.  Visitors are always welcome!

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