As you drive down the freshly paved roadways of the new Fremaux Avenue interchange in Slidell, take a look at the thick green carpet of grass on the embankment.

Planting and landscaping are usually the last steps of any construction project. Before the grass comes in lush and full, a process known as hydromulching is used to distribute seed and fertilizer evenly across a large area.

It’s the unnaturally bright green substance often seen covering the slopes, medians and other parts of the highway. It was first developed in the 1950s, as the interstate highway system began its rapid march across the country, and a more effective method of restoring the disrupted landscape was needed.

Highway workers apply hydromulch to the embankment of Slidell'€™s new Fremaux Avenue interchange recently. (Staff Photo by Anne Lautzenheiser)

Darrell Hall, owner of Economy Grassing in Ethel, has been working with hydromulch for at least 20 years.

“When we first started it was almost pure sawdust,” said Hall, whose company is contracted for the Fremaux project. “It was constantly clogging the pumps, and we had lots of problems.”

The mulch is a cellulose-based wood pulp, just one step above paper. After seed and fertilizer are laid down with a tractor, the mulch is then mixed with water into a thick slurry and sprayed over the seed to protect it from wind and rain until it can take root.

It’s dyed a bright color to ensure even coverage, and the tint can range anywhere from light blue to forest green.

Dozens of companies manufacture hydromulch, and it has numerous applications. In addition to state and federal highway landscaping, it’s used by private developers as well.

“It’s used in new subdivisions, parks, golf courses, things like that,” said Hall. “The Army Corps of Engineers uses it, too, on a lot of levee projects.”

In addition to helping promote even growth, the process helps prevent erosion. While the substance is generally applied using truck-mounted pumps, large-scale applications often rely on aerial spraying.

The U.S. Forest Service recently began using a high-powered helicopter, known as an Air-Crane, as well as several smaller aircraft, to drop millions of gallons of hydromulch on thousands of acres of national forest destroyed by California wildfires earlier this summer. According to an article in the Santa Barbara Independent, more than 1,500 acres in the Santa Ynez Mountains were covered in a matter of days.

Hall’s work takes him all over Louisiana. There’s a bit more planting to do on the Fremaux project, after which his crew will head to the northern part of the state.

“The seeding and planting is always the last part of a project,” he said. “When you see that bright green stuff, you know it’s almost done.”