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VENTURA FWO: Sheet Mulching Experiment Validates Technique for Schoolyard Habitat Projects
California-Nevada Offices , February 9, 2015
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Biologist Colleen Draguesku, of the Ventura Fish and Wildlife Office, applies sheet mulching around recently planted native plants.
Biologist Colleen Draguesku, of the Ventura Fish and Wildlife Office, applies sheet mulching around recently planted native plants. - Photo Credit: USFWS
Roanna Prell, of Ventura Master Gardeners, prepares corrugated cardboard sheets to use as barriers for the sheet mulching expirment in March 2013.
Roanna Prell, of Ventura Master Gardeners, prepares corrugated cardboard sheets to use as barriers for the sheet mulching expirment in March 2013. - Photo Credit: USFWS
This bio swale, covered in stones, has an under layer of cardboard to prevent weed growth.
This bio swale, covered in stones, has an under layer of cardboard to prevent weed growth. - Photo Credit: USFWS
A view of the test area in January 2015, showing the sheet mulched section remain weed free.
A view of the test area in January 2015, showing the sheet mulched section remain weed free. - Photo Credit: USFWS

 

By Jon Myatt

Weeds. Anyone that has ever planted a garden or installed some landscaping has had to confront them. They pop up everywhere. They invade vegetable gardens and overtake flower beds. 

And in the drier valley east of Ventura, Calif., between the Los Padres National Forest and Santa Monica Mountains, where growing conditions are less desirable, weeds are historically problematic, especially on native plant restoration sites. 

It’s a situation that Michael Glenn, a biologist with the U.S. Fish and Wildlife Service’s Partners for Fish and Wildlife program, had been struggling with in his own native plant, pollinator garden.  As a biologist that coordinates Schoolyard Habitat projects  using native plants, he had been receiving calls from many of his project partners concerned about troublesome weeds overtaking all the work they’ve done.   

Making things worse were local watering restrictions as a result of California’s drought.  This compounded the weed problem for his Schoolyard Habitat projects that students and teachers were conducting. Those projects were in danger of turning to patches of weeds. 

“It was a challenging situation,” he explained. “I thought about trying a technique I used at home, in my own garden -- a layer of cardboard, under a layer of mulch.”  

While that technique, known as “sheet mulching,” had been successful for Glenn at his home, he needed to validate the process before recommending it to partners for use in their projects.  So he took the idea to the Master Gardeners of Ventura.  

Glenn described the concept to a group of Master Gardeners when visiting a restoration project at the California Veteran’s Home outside of Ventura in February 2013. He suggested that an experiment to demonstrate the effectiveness of sheet mulching would be helpful. 

Roanna Prell, with help from Master Gardeners Dale Dean and Leon Daniels, decided to take on the experiment. She intended to test the effectiveness of using sheet mulching versus mulch alone to retard weed growth.  

“We defined sheet mulching as a treatment that consists of layers of cardboard placed on the soil and covering any unwanted plant material already growing, then, covering it with mulch that is made of ground-up woody plant materials,” Prell explained. 

On February 15, 2013, Prell and Dean measured and staked out a test area into 3 equal squares, each 10 ft. by 10 ft.  For the cardboard layers, Prell obtained discarded corrugated cardboard boxes from the Veterans’ Home kitchen, and when prepared into flat pieces, the sides with ink printing would be placed face down. 

Yellow cording was strung around the site, with flags placed at each stake to differentiate each area. Photos of the weeds were taken to document the type and density of weed cover. Each square was color coded: yellow, blue, and red. 

The red area was covered with 3 inches of chipped bark, no cardboard. Then a few days later, Master Gardener Leon Daniels and Prell placed corrugated cardboard in each of the two remaining squares. The blue square received 1 to 2 layers of cardboard, completely covering the area, but with some hairline gaps between pieces. The yellow square received 2 to 3 layers of cardboard, with no gaps. Both areas were wet down before 3 inches of chipped bark was placed over the cardboard in both the blue and yellow sections.

“Our goal, and our hope, was that soil covered with sheet mulching would retard weed growth more than mulch alone,” explained Prell.  “And we needed to identify how significant, if any, the improvement would be.”

The test period was a full year. So they watched -- and waited. They didn’t add water to the area over the test period, allowing for natural conditions to drive the experiment.  And periodically, from one spring season to the next, they observed, documented and photographed. Finally, on a sunny morning in March 2014, the results were in. “Hypothesis confirmed.” 

 “Some break-through weeds were found along the borders of the red and blue sections, as we expected,” said Prell. “And there was just one weed coming through the yellow section.” 

 “The mulch section without cardboard contained 110 weeds; the multi-layer section had just one,” she said. 

With the experiment completed, Glenn felt confident recommending the technique for other restoration projects with similar weed problems.  

 “Thanks to the Master Gardener’s findings, we are now using sheet mulching at every new Schoolyard Habitat project,” he said.  “Every potential Schoolyard Habitat site in this area has a significant weed problem.” 

“I specifically target the unsightly, problematic, weedy spots at each school,” he added. “I want our program to solve problems for the school.” 

Sheet mulching, using readily available cardboard, can improve every landscaping or gardening project by decreasing maintenance, and according to Glenn, it is essential for project sustainability. 

Sheet mulching “greatly inhibits weed growth, retains moisture in the soil, allows the beneficial organisms to thrive in the soil and increases soil porosity,” he explained. “It also makes it much easier for students to plant and it looks nice too.” 

“Schoolyard Habitat projects can be used in so many ways to enhance student learning, whether it be bringing classroom lessons alive using hands-on materials, using the habitat as simply a place to learn, or in this case -- conducting valuable research for best management practices in habitat restoration,” added Carolyn Kolstad, the U.S. Fish and Wildlife Service’s National Schoolyard Habitat coordinator. 


Jon Myatt serves in External Affairs as the Digital Communications Manager for the Pacific Southwest Region.


Contact Info: Jon Myatt, 916-414-6474, jon_myatt@fws.gov
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