By Janis Keating

Considering the odds stacked against them, it’s a wonder that any reclaimed site manages to revegetate. In the average garden, new plants are gently dug into the soil, they’re watered faithfully, and weeds are meticulously pulled out, all to allow the new plants the best possible chance to grow and thrive. The average roadside or hillside gets seed, fertilizer, and a little mulch; other than the moisture that is applied with the seed, the site often must “make do” with whatever precipitation comes its way. Unfortunately, this procedure, while cost-effective, often costs more in the long run, as the site may have to be reseeded at least one more time. In response, many contractors are adding increased soil amendments at the outset, to give the seedlings a better chance to establish and grow. Despite higher upfront costs, the extra additives often allow the site to revegetate in one pass.

In a Hurry? Use a Slurry!
Bob Mark of northern California’s Mark Seeding Service explains his surefire process for revegetating a site. “When we hydroseed a site, most of the time, amendments are applied with the seed. Depending upon the site’s needs, we make a slurry of some sort. For example, we add compost—this is mostly done on marginal soils. We usually add a thick slurry, half an inch to 2 inches deep, which also contains wood fiber and tackifier.

“Wood fiber carries the seed, compost, fertilizer, and tackifier, so all are evenly distributed. Because it’s a different color, wood fiber also allows the applicator to know where he has applied it. The fiber forms a matrix to hold the seeds together, and compost makes a medium the plants can get established in much more easily. Cut slopes, which have been recently opened to the atmosphere, are usually anaerobic, but the plants need to have oxygen. To solve that problem, we put artificial strata on the soil so seeds can get started. Something must be added to the subsoils, because they’re usually sterile—no nutrients or bacteria. Even if seed germinates on such an untreated site, it will not prosper.”

Mark obtains many of his soil amendments from Horizon in Rancho Cordova, CA. “We use compost engineered for this type of work, which contains high humus and humic acid, both of which beneficial bacteria feed on. Horizon provides us with Biosol, which contains lots of enzymes and nutrients that will feed bacteria. On certain sites, we also might use mycorrhizae inoculums, which produce fine thread-like fungus in the soil. They attach themselves to plant roots and allow the plants to pick up the nutrients that are out there.”

Problem sites require a specific slurry mix. “We worked a project in Richmond, California, near San Francisco, on the east edge of the bay, which entailed reclaiming tidal marshes. Marshes are important to the bay; tidal marshes filter nutrients, clean out all the sediment and pollutants that come from city, or streams; and stop these items from getting into the bay. Marsh plants can take zinc, cadmium, and lead and store these minerals, which can clean out the industrial waste, reducing the concentration of the problem metal. Local birds use the marshes for breeding; also, small crustaceans, which the birds eat, live there, so the marshes are very important to area wildlife.”

As this area was once used as shipyards, there was plenty of debris and metals that needed to be removed. The area also needed manmade features installed that would allow a marshy environment to recur. Tides needed to be controlled so the marshes wouldn’t be overwhelmed; the area also gets westerly winds from the direction of the Golden Gate Bridge, so the site needed to be somewhat sheltered. Mark explains the process: “Separation berms 12 feet wide and 3 feet above high tide were put in to control flow for the tidal marshes. Of course, a marsh needs plants as well as water, but, because this was a very salt-laden environment, marsh workers never got anything to grow on the berms. When we were called in on the project, they scraped off the top 2 inches of salt-laden soil, and we sprayed a solution which allowed the salt-tolerant grasses to get a hold on those slopes. Some success has already come from that process.

“We needed to use organic matter and different biological resources, not just regular hydroseeding,” he goes on. “The ‘usual’ slurry of just seed, slow-release fertilizers, tackifiers, and fibers would not have done the job for this site.”

Mark Seeding Service does quite a bit of work for the California Department of Transportation (Caltrans), including remediation of landslide sites. Such projects also entail a certain amount of “creative composting.” “Caltrans would cover the area with a netting; then we’d put slurry atop—or even sometimes under—the spun plastic netting or excelsior—usually aspen fiber.” The fiber anchored the soil and the slurry to the site, giving new vegetation a head start.

Mark’s firm handles projects in northern and central California, and after amending several different types of soils and seeding many varieties, he’s come to the conclusion that, in addition to fertilizers and compost, “using mycorrhizae is important. Companies grow one mycorrhizae species for elms or oaks, one for different types of grasses, and so on—matching mycorrhizae to a plant greatly extends that plant’s ability to get nutrients over a much wider area. For the salt-tolerant grasses used in the marsh application, we used a six-part slurry: seed, slow-release fertilizer, fiber, tackifier, organic compost, and mycorrhizae inoculants. Such a slurry is also laid on a lot thicker.” As for compost, Mark doesn’t have to purchase a fancy grade; he utilizes greenwaste, such as yard trimmings.

Although he’s rightfully proud of his company’s solutions, Bob Mark gives credit where it’s due: “Caltrans set the trend of these products. Due to the set of specifications it’s generated—such as that so many micro- and macronutrients must be present in the soil, and you have to have the soil in a certain pH range—oftentimes we have to apply 3,000 or 4,000 pounds of compost per acre. But the end result is well worth the effort and expense.”

Jay Selby, president of Selby’s Soil Erosion Control in northern California, also does his share of Caltrans work. “We do sprayed-on applications—mostly hydroseeding and straw blowing, but we also use rolled erosion products, such as wattles and blankets,” he explains. “We also service drainage inlets and do consulting work. Horizon provides us with wood fiber, tackifier, granulated fertilizers to mix in our hydroseeding tanks, bales of BFM [bonded fiber matrix], and liquid polymers for dust control.”

Selby’s crews diagnose each site by its soils and its topography, to choose which erosion control method will work best. “We usually mix our own matrix, comprising fiber used in conjunction with EarthGuard polymers. We like EarthGuard instead of pre-manufactured BFMs because we use our own fiber, which we have on hand, and mix it with liquid polymer. We order truckloads of fiber—recycled newspaper mixed with recycled wood, and wood fiber alone—for everyday use; then, as we need it, we’ll mix it with polymer.”

Photo: Jay Selby

Quite a bit of dust can be created during straw blowing.

Despite all his experience, sometimes Selby will need advice for a problem project. “In extreme cases, for highly susceptible areas, we consult with Horizon to find the right type of EC blankets to use. Of course, Caltrans has standards of what we can use and Horizon is a good source—they know what’s approved.

“Most everything here has a written specification,” Selby says. “Because of totally different climates and rainy seasons, in northern California we mainly use hydroseeding, straw, and tackifiers. In the southern part of the state, we usually use liquid polymers and BFMs.” He adds, “Northern California leads the US in the highest standards of EC practices; everyone else is five years behind us. This is likely due to the developments in the [San Francisco] Bay Area; drains go to sea, so you get huge fines if you don’t prevent pollutants from getting into the bay.”

However, these high standards can also be at cross-purposes to one another. “The Water Quality Control Board requires one thing, and the Air Quality Control Board fights us, causing problems with straw blowing in certain counties. It’s almost a joke here—air- and water-quality control are in the same building, yet they can’t get together and agree on standards. Water quality requires us to blow straw, but air quality fines us for doing so, because it creates too much dust. At many sites, we have to change to EarthGuard or BFM to avoid the fines, which are really steep. We’re now changing from straw, and also changing our specifications. Customers sometimes get upset, as we’ve done their projects for years, with one material, for one price—but now we have to charge them more because we have to change the materials.”

Myco-rising Expectations
Adding fertilizer and compost may not be all that’s needed; if for some reason the plants can’t absorb all the tasty ingredients around them, a fill-up of fungus should do the trick.
Located in Grants Pass, OR, Mycorrhizal Applications Inc. produces several dozen types of mycorrhizae—fungi present in most healthy soils that help plants make use of the nutrients around them. “We try to mix and match mycorrhizae for various plants or environments or different needs,” explains Dr. Mike Amaranthus, president of the company. “We make mixes for our clients and the site conditions. We use seeds of mycorrhizae and their spores. Depending on the variety, some are large, to half a millimeter in size.”

The beneficial fungi are sown and grown, much like any other crop. “We use them with living host plants, depending upon what kind we want to grow, and then we harvest them from the soil. We sell around a half-million pounds a year,” says Dr. Mike, as he likes to be called, who has been working with these fungi for 30 years.

Will just “any” fungi do? “Some mycorrhizae grow well with many plants, but others only like certain plants. Matching the right variety to the plant produces the best results,” he explains. After combining with a plant’s roots, mycorrhizae will extend anywhere from half an inch to 3 or 4 inches from the root itself. “Their job is to get the soil moisture and nutrients for plants,” he says.

In some cases, mycorrhizae are already present in the soil. “Before taking on a project, often we’ll take a sample from a particular site or plant to our lab, to see if mycorrhizae are already on the site. That will help us determine the need and make recommendations from there. More often than not, however, if the site is disturbed, you will need mycorrhizae.”

Not every plant requires mycorrhizae to perform at its best. “We have a good handle on the needs from the scientific literature—there are currently 60,000 studies of these critters—on which plants need mycorrhizae and which don’t. On our Web site, you can use the ‘ASK’ function to find out if the plants you’re trying to grow need them.”

In addition to facilitating plants’ ability to use soil nutrients, mycorrhizae produce glomilin, a chemical that “glues” soil grains together, improving the soil’s condition.

Mycorrhizae are available in many forms. “Some products are granular, much like kitty litter. Others come in a powder, or even a liquid suspension. The average application is about 10 pounds of powder per acre.” What do the mycorrhizae live on, between harvest and incorporation? “They’re dormant,” Dr. Mike explains. “They’re not alive like bacteria that are alive—until they get near an active root.

Photo: Jay Selby

Selby used coir blanet in this detention basin.

“Once they’re in a plot, and conditions remain favorable, mycorrhizae propagate in the soil; they don’t have to be reintroduced,” he goes on. “Some varieties will eventually form mushrooms and puffballs, especially the ones we use for trees. Mycorrhizae might take five to 10 years to get to the puffball stage, however. Spores are also individually made in the soil subsurface.”

Although inoculation might be costly at the outset, it’s cheap in the long run. “We’re not looking for a quick fix, but a long-term solution,” he says. “It costs big to go back to a site and seed it again, but our treatment allows them to do it just once.”

With a name like Amaranthus, it’s ironic that Dr. Mike got interested in his chosen field. “Amaranthus—known to some gardeners as Joseph’s coat—is one of the few plants that don’t use mycorrhizae,” he chuckles.

Friends of Fungi
Dave Russell, a Bureau of Land Management (BLM) agent in western Oregon, uses mycorrhizae when reestablishing wooded areas. “We’ve also used it in an orchard application, with established trees in old agricultural soil, but we don’t know the final results yet.” The BLM has also used mycorrhizae in its greenhouses. “We’ve noticed increased feeder roots, and our Ponderosa pine seedlings enjoy increased survival and growth.”

Russell notes that in most forests, mycorrhizae are naturally occurring. “But in a new forest plantation, if mycorrhizae are there already, you don’t have to worry; you can go and grow. Otherwise, you have to wait for some time. Mycorrhizae increase establishment and survival rates, both on bare-root and container plants and trees. I’m generally pleased with the results thus far, but I don’t have any scientific papers on these projects. However, our office did do a paper on mycorrhizae with grasses; we found it very helpful after wildfires. The fast growth prevented erosion on some sites.”

As southwest Oregon experiences a “droughty” climate during its hot summers, he says, “Anything that helps with water intake, as mycorrhizae does—we need that tool! Last year we had 29 days over 100 degrees. And this highly varied soil—some clay, some sandy loams, some volcanic soils in the Cascades—needs all the help it can get.”

Local Fungi + Local Flora = Success
In Portland, OR, US Forest Service Revegetation Specialist David Steinfeld not only uses mycorrhizae in his everyday tasks, but he’s also performed studies and co-authored papers on the subject with Dr. Mike.

“We do federal highway projects, trying to get native plants to flourish,” he says. When asked for his definition of “native plants” (a term that can vary, depending on the client and on government mandates), Steinfeld replies, “Locally collected genetic sources of material. We’re not only looking for species local to the Pacific northwest, but also collected from a seed source that has adapted to our local area.”

Photo: EarthGuard

Cover was changed from straw to EartGuard becasue of straw dust collecting on nearby homes.

Steinfeld offers an example: “Douglas fir grows in all western states, but we have to get our seedlings from a local source. After a forest fire, when we’re putting trees back in, we must get trees from seeds collected locally—and we also match geographic area and elevations. A seedling grown for a 4,000-foot elevation is not adapted to a site 8,000 feet up.

“In the southern US, if you’re working with pine, you have the same sandy soil and no elevation changes to speak of,” he continues. “On the other hand, Oregon has rugged terrain, and our south and north slopes can produce a drastic variance in temperature. Put temperature probes in the soil of a northern slope at a 6,000-foot elevation, versus one at the same height on a southern slope, and you’ll find the south stays warmer for six more weeks. From a practical standpoint, you can plant south slope trees in the fall, as temperatures will still be warm enough for root growth.”

Steinfeld’s office has experienced a lot of success by matching seeds and mycorrhizae to a site. “Before the whole northwest timber thing stopped, I worked at a place that grew millions of seedlings a year. Seventy-five percent of them took because we matched seedlings to sites. On the other hand, there’s a whole industry of seed growers who find this matching process a hindrance.

“There are many past examples of mistakes, like in the 1960s, when nurseries would send out seedlings from Montana, which would grow, but then all of a sudden the plants would fall apart. Matching seeds and mycorrhizae to a site is not a theory; we’ve seen this work.
“I was in Argentina, where they used our Oregon tree species, having them grow in places where their native plants won’t grow because they’re not yet acclimated. I’ve used mycorrhizae in highly disturbed areas—you see, I’m your ‘last resort guy.’ I’m who you call when you have areas with no topsoil or extreme burns, when the local flora and fauna are gone.”

His office also uses mycorrhizae in hydroseeding. “In addition to trees, we plant grasses on high-elevation sites. We’ll put mycorrhizae in the tank with the fertilizer and the grasses which grow in our forest.” For tree seedlings, mycorrhizae can be incorporated in the nursery, by applying spores into the soil and washing them in. Small trees can also be banded with mycorrhizae, as one does with fertilizer, or inoculants can be added in the field, by putting a bag of mycorrhizae into the hydroseeding tank or inside the hole with the tree.

“Mycorrhizae will not change your site; they’re not the ‘magic bullet,’” Steinfeld says. “Give me a good soil and you’re set. If the soil is poor, and you have the money, we can bring in topsoil and compost. Adding just fertilizer to the hydroseed mix won’t do it all—soil depth, water-holding capacity, and organic composition are all needed, and mycorrhizae make that possible for the plants. Mycorrhizae mine the soil for phosphorus, a tough nutrient to get out of the soil. They also help soil structure and infiltration rates, which slows erosion. I’ve done studies with Dr. Mike and I know it works.”

In the September/October 2003 issue of Erosion Control, Amaranthus and Steinfeld published an article (“A Symbiotic Relationship”) that included a study of mycorrhizae’s effectiveness with native grass seed. Four plots were grown: One received only mycorrhizae; the second, mycorrhizae plus a slow-release fertilizer; the third, slow-release fertilizer only; and the last received neither amendment. Interestingly enough, the mycorrhizae-only plot usually outperformed the mycorrhizae plus slow-release fertilizer plot—a concept that seems a little counterintuitive to the average grower. Doesn’t fertilizer (the study used an 18-6-12 mix) always aid plants?

“If there’s lots of phosphorus around, mycorrhizae don’t develop. They make phosphorus available to the plant, and if it’s already in the soil at concentrations of more than 70 parts per million, that stops them from growing,” Dr. Mike explains. “In essence, they’re getting overfed. Mycorrhizae use low to moderate levels of phosphorus; added nitrogen and potassium had very little effect.

“Including mycorrhizae saves money on how much fertilizer and water you have to use,” he goes on. “Using less fertilizer also ensures you’re not harming the soil, as lots of these fertilizers are salts, which poison the soil. You’re decreasing your input costs, and the mycorrhizae stay put, unlike fertilizers.”

Is the benefit worth the cost? Steinfeld thinks so. “We spend a hundred bucks an acre, and that’s pretty cheap insurance, as I’m already putting thousands of dollars in each acre.”

Janis Keating is a frequent contributor to Forester Communications publications.

EC - September/October 2006