© 2009 Wendy Dager

According to the online information site Answers.com, geotextiles are “woven or nonwoven fabrics used with foundations, soils, rock, earth, or other geotechnical material as an integral part of a manufactured project, structure, or system. Also known as civil engineering fabrics; erosion control cloth; filter fabrics; support membranes.”

On that same Web site, hydroseeding is defined as “a method of sowing grass seed in a stream of water aimed at the ground to be covered. It is particularly useful for large-scale properties or land that is on a steep hillside.” Those definitions seem markedly different, but each of these applications serves a similar purpose in that they are both widely used by landscape contractors to reduce erosion on embankments and other areas prone to stormwater runoff.

The problem, according to S&S Seeds’ Paul Albright, is that many erosion control experts continue to use expensive geotextiles, because that’s what they’ve used in the past, rather than switching to the more cost effective method of hydraulically-applied seed.

“It’s like delivering a pizza in a Ferrari,” said Paul. “The Ferrari looks good, but is an expensive way to do the same job a less fancy car could do.”

Standard hydroseeding with seed, fiber mulch and tackifiers can run as little as 2.5 cents per square foot, while a geotextile is 20 cents and up per square foot.

Indeed, there are situations in which a geotextile is best for stabilizing a hillside, such as when the growing season is short, at high altitudes, or where major storms are a frequent occurrence (see the Leaf-let’s 1997 article “Sweeping Erosion Under the Rug,” http://www.albrightseed.com/sweeping.htm).

“But, in California, where the growing season is year-round in most areas, it makes much more sense to hydroseed,” said Paul.

There are three points to consider when selecting the proper method of seeding a hillside.

1. Functional longevity
2. Slope length
3. Slope gradient

While the second and third points are of extreme importance because water travels at a greater velocity when the slope length and gradient increase, causing larger erosive forces, it is the first point—functional longevity—that is the most critical. Functional longevity is the ability of the applied material to last and to hold until plants are mature enough take over for the mulch or erosion control cover, creating the needed soil stabilization.

“Hydroseeding is usually the Best Management Practice for erosion control on a job site,” said Paul. “Geotextiles are not only overkill in terms of initial cost, but there can also be hidden problems that might create even more expense in terms of maintenance, as well as correction if a failure occurs.”

With geotextiles, there have been incidences of failure because of the complexity of their installation. For instance, geotextiles are subject to “tenting” over rocks and stumps, and there is the possibility of shrinkage or lifting of the fabric from low spots.

With a hydraulically-applied slurry, the particle-by-particle conformation effectively covers irregularities of grade and surface.

When there is a crust failure of a hydroseeded surface, the damage is visible and can be easily and inexpensively repaired. Geotextiles often mask slope failures and are not detected until stormwater runoff damage becomes obvious.

Stormwater runoff leads to pollution in addition to erosion. It’s up to landscape contractors and other industry professionals to choose the right method of protecting hillsides and other sites.

In addition to being able to create a custom blend of seeds for every application, S&S Seeds has a number of hydraulically-applied tackifiers from which to choose, including Flexterra FGM, Terra-Matrix SFM and HydroBlanket BFM (http://www.ssseeds.com/other_products_bottom.html).

“While tackifier technology has certainly advanced over the years, it’s not a new concept,” said Paul. “In the 1970s and ‘80s, Burgess L. Kay of University of California, Davis spent years studying tackifiers and releasing results about their effectiveness.”

Some of Kay’s studies can still be found online, including “Tackifiers for Straw Mulch,” a document dated February 15, 1975 and released by the U.C. Davis as part of their “Agronomy Progress Report.”

“I consider Kay one of the pioneers of comparative erosion control testing,” said Paul. “Which is something we at S&S Seeds continue to honor by constantly following up on what’s new in the industry as well as conducting our own studies with the test plots at our Los Alamos growing facility.”

At S&S Seeds, the goal is to provide our customers with the best information and the most cost effective way to approach every project.

For more information about hydraulically-applied seed, tackifiers and other erosion control products, visit our Web site at http://www.ssseeds.com or call our helpful staff at (805) 684-0436.

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