Plastic tarps are appearing around the park again. They are being used for a process called solarization. Solarization involves removing the visible plant matter, ensuring the soil has moisture, and then finally placing a plastic tarp over the area and weighing it down on the edges to trap heat and moisture. During the day, light from the sun passes through the tarp and transforms into heat as it is absorbed, heating the top 6 inches of soil up 140°F in the summer sun and reaching temperatures as high as 99°F a foot and a half below the surface (soil temperatures are usually around 90 degrees this time of year.)
In addition to killing off unwanted plants and parasites, solarization increases the speed at which organic material is broken down, enriching the soil with nutrients such as nitrogen, calcium, potassium and magnesium (similar to a compost bin). After several weeks the tarps are removed and the soil is left bare and fertile, ready to be reused.
Here in the park, Park Naturalist Jewell Cozort, along with Weed Warrior Volunteers, laid down sections of tarp in the Savanna in order to kill invasive Johnsongrass. The Master Gardeners have done the same in the Children’s Vegetable Garden in the Voelcker Historic Homestead to remove weeds in the walkway between vegetable beds. The tarps will be removed in late September. The area in the Savanna will be replanted with wildflower seed. The pathway in the Children’s Garden will be re-mulched to provide a pathway to the garden boxes.
Solarization is a great alternative to spraying chemicals to kill unwanted vegetation, but it takes time, patience, and a little ingenuity. You could try this at home in your garden.
Plastic tarps allow sunlight through to heat up and quickly kill the roots below. You could also use old newspapers or cardboard boxes to completely remove all light to the soil, thus starving the plants. The blackout solarization method works well when the temperatures are lower.
If you are interested in giving it a try, check out Texas AgriLife Extension’s how-to guide on summer solarization.