July: El sol

Solar flares, summer solstice, la luna y el sol…we are talkin’ solarization. It’s hot out there in the watershed this time of year. Whether you’re experiencing the suffocating urban heat island effect in Washington D.C., Richmond, VA, and Lancaster, PA…or the open fields of central Maryland, the sun is impacting you.

While the old “hack and squirt” herbicide spray method works very well on controlling invasive species in your backyard, woodlands, or in between your raised beds–why buy chemicals which require repeated maintenance, when you can use and re-use a black plastic tarp and the power of the sun, all in one go? The process of solarization (white tarp) and occultation (black tarp) involves cutting invasives down before laying a tarp over the affected area for several weeks, a minimum of 6, but the longer the better–effectively baking the rhizomes under the ground and preventing the photosynthetic process above. During the summer months, heat is absorbed under the tarp and can reach up to 140 degrees Fahrenheit on the surface and close to 100 degrees Fahrenheit two feet below the surface.

Occultation, Photo: hardwickgazette.org

Some invasive species spread rapidly through the use of underground stems called rhizomes which are harder to target and control. Examples of invasive species with rhizomes include: Japanese barberry (Berberis thunbergii), Common reed/phragmites (Phragmites australis), Kudzu vine (Pueraria montana), English ivy (Hedera helix), and Wiregrass (Cynodon dactylon) among many others. These invasive species are a nuisance particularly because they outcompete native plants for space and resources and cause severe economic and ecological damage.

Wiregrass (Cynodon dactylon), originating from warmer climates, is an invasive species that is particularly hard to rid due to its drought-resistant properties, widespread underground rhizome network, and ability to colonize sunny areas quite quickly.

Bermudagrass. Photo: Betty Marose

In urban farms, where resources and funding are tight and labor may be volunteer-based, methods for weed control are always of high priority. Key factors contributing to action plans may also include effective management on a small-scale farm and reduced chemical use for community health and well-being.

On Common Good City Farm, a regenerative urban farm in Washington, D.C., the community is at the forefront of all the work they do. From volunteer events to garden parties and cooking classes with fresh vegetables grown on the farm, to upcycling and herbal workshops, and sliding scale seedling and Community Support Agriculture (CSA) opportunities, their mission is simple–to provide equitable food access, sustain their farm for generations to come, and create youth programs and adult educational opportunities to connect the DC community.

Common Good City Farm, Photo: Jillian Everly

Given the various, small-size plots on the farm–there are many patches of land and long rows utilizing the methods of occultation and solarization. We uncovered the prescribed sunflower patch in late April to reveal the payoff of using a black plastic tarp weighed down with objects such as bricks and rocks.

A tarp covering a plot for several weeks, Photo: Jillian Everly

The treatment area uncovered, Photo: Jillian Everly

Miraculously, our friend, the sun heated the ground to temperatures unsuitable to Wiregrass survival and the black tarp prohibited the photosynthetic process and therefore the plant’s ability to utilize sunlight in the production of food for itself. The photo of the treatment area unveils a distinct border of where grass was covered versus left uncovered.

Further inspection of the soil revealed various species of detritivores such as this centipede, who moved in to feed on dead organic material. Through the decomposition process, the detritivores are able to break down complex organic compounds into simpler forms, facilitating the release of nutrients back into the soil to be used by native plants such as in this plot’s case, sunflowers.

Centipede, Photo: Jillian Everly

Curious how well the sunflowers grew from late April to July or if Wiregrass re-colonized the protected patch? Email me at jeverly@allianceforthebay.org

A farm assistant and volunteers plant sunflowers. Photo: Jillian Everly

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