Using Prescribed Fire to Control Invasive Species
October 2025 | Horticulture & Conservation
In this blog you will learn about the prescribed fire that was administered at Pittsburgh Botanic Garden on October 15, 2025. To learn more about some of the terms used in the article, please reference the “Learn More” section on the sidebar or at the bottom of the page on mobile.
The First Step: Early Detection, Rapid Response
In 2023, Pittsburgh Botanic Garden’s Horticulture & Conservation team discovered a problem. While doing routine garden work, they spotted a semi-woody perennial called Lespedeza cuneata encroaching on several garden areas. As careful stewards of the land, the Garden adheres to a principle called “ecological landscaping.” This approach to gardens and landscapes considers the ecology of the site and maintaining it in a way that enhances the benefits to humans and other living organisms in the ecosystem. A key component of this practice is “early detection, rapid response” for non-native plants that negatively influence local biodiversity In this case, the Garden took immediate action to check the spread of L. cuneata before it would be able to overtake large portions of the land.
Lespedeza cuneata, also known as Chinese Bushclover or Sericea Lespedeza, in Margaret Lawrence Simon Dogwood Meadow. (2024) Credit: Pittsburgh Botanic Garden
Why do we need to control Lespedeza cuneata?
This perennial in the legume family is not native to southwestern Pennsylvania; it originates in eastern Asia. It was brought to the United States in the late-1800’s where it was primarily used for soil stabilization and revegetation mixes. After escaping the areas it was originally planted, it became evident that this was a particularly aggressive spreader.
Lespedeza cuneata is multi-faceted in its approach to taking over a landscape. It is a semi-woody plant, making it strong and durable through many weather conditions; high in tannins, making it unpalatable to most animals; allelopathic, generating chemical compounds that inhibit the germination of other nearby plants; and it forms large, dense stands that serve as seed repositories. A single L. cuneata plant is capable of producing thousands of seeds, spreading exponentially when left untreated.
In order to protect native plants from being out-competed, the Garden got to work immediately on an integrated invasive species plan with the goal of supporting biodiversity and allowing native species to thrive.
An Integrated Approach to Invasive Species Management
While Lespedeza is an extremely successful and competitive plant, humans have many tools available to control it. Pittsburgh Botanic Garden examined the current research and found that the most effective approach for Lespedeza cuneata would have to be an integrated plan consisting of multiple management techniques. Some of the techniques the Garden considered are:
- Mowing: Cutting down the plant at the right time of the year can prevent the plant from making viable seeds. While certainly helpful and effective, this method does not address the seeds that may already reside in the seed bank or in the top layer of soil.
- Grazing: Introducing animals to the landscape is extremely effective for controlling many species, but this particular species is unlike many others. The tannin content in Lespedeza cuneata makes it unpalatable for many grazing species.
- Seeding: Overseeding with more competitive plants can effectively “choke out” the L. cuneata plants, not allowing them the necessary resources to live and continue to spread.
- Chemical Control: Synthetic herbicides can be used to kill Lespedeza. This approach comes with several other risks, however. Many synthetic herbicides can cause unintended ecosystem damage and downstream impacts. Pittsburgh Botanic Garden only resorts to chemical controls as a last resort, and chose to pursue a prescribed fire to test the effectiveness of another non-chemical practice.
- Prescribed Fire: Prescribed fire has been used as a land management tool for generations, but has not occurred in Allegheny County since its inception. As fire sweeps through the landscape, it creates a more even playing field for native plants to bounce back, reclaim their space and force out invasive species. Burning also recycles vital nutrients back into the soil and promotes the growth of trees and shrubs that may be stressed by dense vegetation drawing resources away from them.
Pittsburgh Botanic Garden’s integrated approach includes a combination of nearly all of these practices, as any one would prove to be insufficient in either weakening or ultimately eliminating the presence of Lespedeza cuneata. Shortly after discovering the plant in 2023, Horticulture & Conservation staff first mowed in the spring of 2024, then treated with horticultural vinegar in fall of 2024. Although this slowed the plants growth, germination studies would ultimately show that these treatments did not prevent the plants from producing viable seeds.
Administering the First Prescribed Fire in Allegheny County
In October 2025, Pittsburgh Botanic Garden and Nature Works LLC out of Shepherdstown, West Virginia conducted the first prescribed burn ever in Allegheny County. This project was more than two years in the making, as Nature Works worked closely with Garden staff to assess the situation, advise on alternative control methods, and ultimately create a burn plan.
Creating a burn plan for a space like Pittsburgh Botanic Garden was a unique challenge when compared to Nature Works’ 20+ years of experience administering prescribed burns in rural areas. Factors like proximity to residential neighborhoods, public visitation on burn days, cultivated plant collections near the burn sites, event rental schedules, and shifting weather conditions throughout various seasons all had to be as aligned as possible to execute a safe and effective fire. Autumn 2025 presented the most favorable balance of these parameters, allowing the teams to establish a projected burn window.
The day before the burn, October 14, Nature Works conducted a site visit to ensure that all necessary fire lines were in place and that conditions on the ground were still conducive to a successful burn. After receiving the “all-clear,” crews proceeded with the burn on the morning of October 15.
In the morning, things were wet. Weather conditions unexpectedly hit the dew point, meaning that more water was present on the vegetation that was set to be burned than crews originally anticipated. The Exhibit Garden was the first unit to be burned. After setting a test fire on a small patch of vegetation, crews began using drip torches to pull fire along the outer perimeter of the burn zone. Fire spread very slowly, struggling to stay ignited as dew was still present on the plants. As the sun continued to rise, the dew dried up, and fire began to spread more efficiently through the Exhibit Garden. After about 5 hours, the burn left behind a mosaic effect of charred ground speckled with some surviving green vegetation.
A portion of the Margaret Lawrence Simon Dogwood Meadow smolders as fire in the center extinguishes and the outer perimeter spreads. (2025) Credit: Scott Goldsmith Photography
After the Exhibit Garden was fully extinguished, crews moved on to the Margaret Lawrence Simon Dogwood Meadow. This space presented a new set of circumstances with swirling winds and drier vegetation after sitting in the afternoon sun. In the center of this garden area was a large, dense patch of Lespedeza that served as a seed repository and from which the plant spread to new areas. As burn crews moved simultaneously along opposite edges of the meadow, individual practitioners walked back and forth using their drip torches to burn the meadow in strips. Once they hit this central patch, the fire began to rage.
This extra hot fire built in intensity and height, all under careful observation by burn crews to ensure the fire did not jump to unintended areas. One of the outcomes Pittsburgh Botanic Garden hopes for, particularly in this patch, is that the temperature from the fire was hot enough to kill off the seeds in the top layer of soil. This would eliminate L. cuneata from the soil seed bank, effectively halting its population growth and presenting an opportunity for the rest of the Garden’s integrated plan to take effect.
Monitoring the Outcomes
Prescribed fire is just another step in the ongoing story of this landscape. Time is the only factor that will truly indicate the success of this burn. Horticulture & Conservation staff will continue to monitor and adapt the next phase of management for any remaining or returning Lespedeza cuneata. If new Lespedeza plants are identified, the Garden will continue to utilize various strategies in alignment with the integrated invasive species plan.
This was a tremendous learning experience for the Garden and all of the dedicated professionals who came out to observe the burn and learn how prescribed fire may benefit the land they care for. Over time, the Garden will continue to update these blog posts and share results and findings on social media. The restorative impact of this fire will be felt beyond the 460 acres under management by Pittsburgh Botanic Garden, serving as an example that prescribed burns can be safely and effectively utilized here in Southwestern Pennsylvania.
Watch this video to learn more and see the prescribed burn in action!
Learn More About Some of the Terms Used:
ecological landscaping
A method of designing, building, and maintaining landscapes that considers the ecology of the site and strives to enhance the benefits to humans and all other organisms in the ecosystem.
Allelopathy
When an organism releases a natural compound that influences another organism. In this case, a plant that releases a toxic substance and inhibits the growth of other plants.
Tannins
Naturally occurring plant compounds that serve a defensive function, protecting the plant from insect or herbivore damage.
Horticultural Vinegar
A high-strength vinegar (acetic acid) solution, typically 20% or more, used as a fast-acting, non-selective contact herbicide for killing weeds. Pittsburgh Botanic Garden used a 45% solution.
Fire Line / Burn Perimeter
Mowed paths used to provide space between the burn unit and surrounding areas, ensuring that burning material is less likely to jump or spread to unintended areas.
Pulling Fire
A technique used by burn practitioners, referring to placing new fire near an existing fire to encourage the flames to join in the middle and helping to control the direction and pace of spreading.
Seed Bank
In this case, refers to a reservoir of dormant or non-dormant seeds that are found in the top layers of soil.
