Solarization — A Promising New Method of Phragmites Control

Phragmites australis, commonly phragmites, is an invasive reed that was first introduced to the United States from Europe over 200 years ago. Although phragmites was among the first visitors to the new America, it wasn't until the 1960's-1980's that it began rapidly invading wetlands throughout the entire Atlantic coast. The Smithsonian Environmental Research Center has investigated the mechanisms behind this sudden expansion and hypothesizes it is due to the establishment of multiple phragmites genotypes in close proximity to one another. They found that by having multiple genotypes among a patch, phragmites was able produce a large number of viable seeds which enabled it to spread rapidly.

Invasive phragmites along the shores of the Chesapeake Bay at the Calvert Cliffs State Park in Lusby, Maryland.

There is a subspecies of phragmites that is native to the United States. At one point you could find it interspersed harmoniously with other native vegetation throughout wetlands. However, the invasive phragmites and native phragmites have hybridized over the years. Invasive phragmites has more aggressive genotypes than the native strands, causing the DNA of the native phragmites to become overpowered by its non-native counterpart. Currently, the invasive phragmites is taking over entire marsh ecosystems. Not only does it create a monoculture that outcompetes native vegetation and provides little food or nesting resources for native wildlife, but it also impairs recreational opportunities and viewshed experiences.

So, what is being done to control phragmites? Herbicide applications, animal grazing, and heavy machinery removal are currently among the most popular control options, though solarization is proving to be an exciting new method for effective phragmites control. Herbicide applications have been successful at phragmites removal to some extent but usually involve between three and five years of consecutive treatments. Additionally, the herbicide applied not only affects the phragmites, but if applied in large quantities, it can also affect other aquatic life and water quality. Furthermore, there has been little success with the reestablishment of native vegetation once the herbicide has been applied and the phragmites is gone.

Using heavy machinery to remove phragmites disrupts the wetland ecosystem by removing the marsh soil and creating disturbed paths on the way to the water’s edge. Animal grazing is one of the least disturbing methods of control; however, there are only so many instances where this is feasible. For example, the wetland would need to be surrounded by pasture or have soil that is stable and topography that is mild enough to support animal access. Additionally, it may be difficult to limit the grazing to invasive phragmites and avoid negative impacts on other native grasses that provide important benefits such as filtering water, buffering the impacts of flooding events, and supplying important food and nesting habitat for wildlife.  

Implementation of the solarization treatment after the phragmites was cut and plastic laid. Note the use of white plastic during an initial solarization experiment. The black plastic was found to hold up better during the solarization treatment.

Solarization has received little attention in the literature world as an effective means for eradication. However, knowledge on the ecology of phragmites and the scope of prior experiments helps shed light on why this might be. Phragmites primarily propagates through a vast network of underground rhizomes. It also can disperse through seeds in early fall, but its ability to spread underground is far more successful. Phragmites also falls slightly behind other native wetland vegetation in terms of life cycle. While plants such as cattails are beginning new growth after the first frost, phragmites is still lying dormant. Therefore, aboveground removal is much more effective if it is completed after phragmites has sent all of its energy stores into its aboveground biomass. Further, it is imperative that removal efforts also tackle the belowground rhizome network to be 100% effective. Most solarization experiments that are cited in the literature have been limited in scope due to the significant upfront time and financial commitment that is necessary to make them successful. Instead of treating an entire patch and allowing enough time for solarization to heat the soil, most experiments have only covered small patches located within larger ones and left plastic on for a period of 6-8 weeks. Unfortunately, solarization, or any removal technique, would have little success in this instance because once the removal is complete the surrounding phragmites will have no problem reinvading before native vegetation can establish.

Solarization site immediately after the plastic was removed.

So, what is involved with the successful implementation of the solarization technique? Solarization utilizes the sun’s ultraviolet rays to heat the soil to temperatures which are detrimental to the underground phragmites rhizome network. This is done by laying thick black plastic over cut patches of phragmites which traps the heat and kills the rhizomes. Therefore, it is crucial to get the plastic on during the hottest months of the year. Although it is recommended to leave the plastic on a minimum of 6 weeks, we have found the longer, the better. Additionally, the use of black plastic prevents sunlight from reaching the phragmites making it unable to complete photosynthesis to generate the energy it needs to re-grow. This depletes the energy stores in the rhizomes and, combined with the increased soil temperatures, completely kills the phragmites. Once spring arrives the black plastic can be removed, and if placed properly, can be reused for future removal efforts.

The same site after solarization implementation showing early regrowth of native vegetation.

To date, we have seen almost 100% eradication and almost no phragmites re-growth after just one year of solarization treatment. While solarization is more time and labor intensive, and therefore more financially costly upfront, it is a one time cost and has been much more effective at phragmites control than common methods like herbicide application. This means that you will achieve eradication much more quickly with the solarization method and will avoid the addition of herbicide to the ecosystem. Perhaps what is most astonishing about the solarization method is that phragmites re-growth at the site has been almost non-existent while native plants have begun to re-establish on the sites just 1-2 years after the solarization treatment was completed.

2 years after solarization treatment showcasing the re-establishment of native vegetation.

The owners of EcoHaven, LLC have successfully implemented solarization in a wetland along the western shore of the Chesapeake Bay. The patches of phragmites were isolated and surrounded by a diversity of native plants. Therefore, once the plastic was removed, the surrounding native vegetation was able to repopulate the site without the need of a supplemental planting. At EcoHaven, LLC we believe solarization is the best method for phragmites control currently available. While most people may stray away from the intense manual labor required, we revel in the sweat and marvel at the beauty once all is said and done. We would love to help you save your marsh ecosystem, and if financial constraints are keeping you away, contact us about finding unique financial solutions.

Bamboo Barriers- A Cost Effective Way to Control Invasive Bamboo

EcoHaven helps landowners across the Mid-Atlantic region remove or control aggressive non-native species that threaten ecological health and property values. One such species is commonly planted by landowners who may not fully understand the impact that their new landscaping will have on their land. Bamboo, which is sold in many cultivars, is often planted by landowners to serve as a fast-growing and year-round privacy fence. While bamboo does create a dense, impenetrable natural barrier of vegetation that will provide a visual buffer from your neighbors, its negative impacts often outweigh its benefits.

                Its ability to quickly establish into dense patches means that bamboo crowds out and kills native vegetation that provides important food and shelter for native wildlife. The aggressive growth habit of bamboo also means that keeping it limited to the desired areas of your property will be an on-going maintenance task. Not to mention your neighbor's may not take kindly to your new landscaping spreading onto their property if you plant it near your property boundary.

                "Running" varieties of bamboo are particularly problematic as they can spread approximately 3-5 feet per year. They accomplish this by sending out underground roots called rhizomes that spread laterally in the soil before sending up a new shoot. These new shoots can grow at an extraordinarily fast rate and the tender young shoots of some bamboo species are actually edible.  Though bamboo is actually a grass, the shoots turn into hard woody stems as they reach maturity and they can grow to a height of 20-30 feet.

                Once established, bamboo can be difficult to remove. Complete eradication can be accomplished by a foliar herbicide application on newly-growing shoots or a cut-stump herbicide application on shoots that have been cut off at ground level. If you prefer to avoid the use of herbicide, excavating the rhizomes of the bamboo can also control the plant but it is imperative to remove all pieces of the rhizomes because any bits left in the soil can re-sprout. Repeated cutting of the shoots can also drain the plant's energy and kill it overtime, but this method takes persistence!

                In some cases, homeowners may want to simply limit the spread of an existing patch of bamboo. This was the case for a recent EcoHaven client who wanted to stop bamboo which was spreading from a neighbor's property onto their property and threatening to block their beautiful view of Hunting Creek. To accomplish this, EcoHaven dug a trench that was 4 inches wide and 30 inches deep and installed 80 millimeter thick high-density polyethylene bamboo barrier along the boundary of the client's property where the bamboo was encroaching.

                Normally, most bamboo rhizomes stay within the top few inches of soil. However, when the rhizomes hit an impenetrable obstruction, such as bamboo barrier, they can grow down deeper in the soil in an attempt to grow around the blockage. By installing the bamboo barrier so deep in the ground, rhizomes from the neighboring property will no longer be able to encroach onto the client's property. Prior to beginning this project, some rhizomes had already spread past the location where the barrier was installed and onto the client's property. Due to this, underground rhizomes that were on the client's property were manually dug out and discarded to keep these from developing into a new stand of bamboo on the client's property.

                After the bamboo barrier was installed in the trench, the trench was filled back in with soil and then leaf litter from the surrounding forest was placed back on top of the disturbed area to prevent soil erosion into the adjacent tidal creek and wetlands. Even after filling the trench, the bamboo barrier protrudes 3 inches above the soil to prevent bamboo rhizomes from growing over top of the barrier and onto the client's property. The client will periodically monitor for "rogue rhizomes" that attempt to grow over the bamboo barrier, but it will significantly lessen the threat of bamboo encroaching on their property and drastically reduce the maintenance involved to keep it that way.

                As a company dedicated to improving the health and resiliency of the environment, EcoHaven commends those who are looking to utilize more natural structures to achieve privacy around their homes. If this is the case for you, we recommend looking for native evergreen alternatives to help achieve privacy while also providing beneficial food and habitat for wildlife. Utilizing native plants in your landscaping will also significantly reduce your maintenance efforts and costs as you will not need to constantly work to keep them contained and they are adapted to living in this region so once established, they do not require maintenance such as watering or fertilizing.

                If you are interested in installing native vegetation to serve as a privacy buffer and provide beauty and wildlife habitat around your home,  consider choosing Atlantic White Cedar or Eastern Red Cedar (which is actually a juniper!) which are both dense evergreen trees that reach a height of 30-50 feet. If you are looking for something a little shorter, American holly provides evergreen foliage and the benefit of red berries that are eaten by many bird species. Cuttings from American holly also make great additions to natural holiday decor! Another option is mountain laurel which is an evergreen shrub that sports large bunches of beautiful white flowers in the early summer. If you need help picking out native plants that are suitable for your site and your project goals, let us know and we would be happy to help you "achieve your ecohaven"!