Seed, mulch, and soil amendments
By Carol Brzozowski
With every project an erosion control specialist approaches, there are a host of issues to consider when revegetating an area. What seed to choose? What soil amendments? How to apply it? When?
When David Gilpin of Pacific Coast Seed collaborates with landscape architects and others who have seeding projects, he attempts to understand their objectives and the environment in which they will be seeding.
Some of the factors clients are asked to consider:
- Planting time
- Number of acres to be seeded
- Objective
- Elevation
- Precipitation
- Vegetation type
- Soil type
- Irrigation needs
- Sowing method
- Use of other erosion control products
- Plant preferences and characteristics
High-Altitude Planting
Soil conditions top the list of criteria Ron Dean considers when choosing seed types for revegetation projects.
“Most reclamation work is done with very poor soil,” notes Dean, who is with estimating and business development for American Civil Constructors in Denver, CO.
For example, the Colorado Department of Transportation does not lay down topsoil before seeding, “so generally speaking, you are stuck with the soils that were there after all of the construction effort is done,” he says.
Microclimate is important in seed selection. “In the mountain regions, we use different seed mixes than we do down on the plains,” Dean explains.
The area in which American Civil Constructors does business is in the high Sierra. “That’s nothing but high-altitude desert, so we don’t have the benefit of rains,” Dean says. “The mountains generally have afternoon showers in the summertime, but down on the plains, we can go days of 100-degree temperatures running with no moisture.”
Foot traffic is also a consideration to a certain extent when choosing seed mixes, he notes. His company plants in a variety of venues, including golf courses.
“When we seed golf courses, that’s obviously a whole different palette of grasses,” he says. “The difference between a rough in our climate and a rough on the West Coast is considerable. When we can, we like to use native grasses that come from the tall and short grass prairies here at 5,000 feet.”
Another factor in considering seed selection is traffic areas. Slow-growing seeds results in areas that don’t have to be mowed as frequently.
“Certainly, highway rights of way have different requirements than mountain passes,” says Dean. “There always is a mow strip along most of the urban rights of way. In Douglas County, south of Denver, the open space program has about five different mixes, all based on height.
“The low-growing stuff is planted along pathways, the intermediates are planted out a little farther, and the tall, leggy grasses get planted in areas that probably are not going to get a lot of pedestrian use, simply because there are rattlesnakes and nasty kinds of creatures that like to hide in the tall grasses,” Dean points out.
Working to Spec
Debbie Turner, president of the Ram-T Corp. in Thorndale, PA, cites many considerations in choosing the type of seed appropriate for a particular site. Her company does commercial and residential seeding projects. Some of the seeding product and application work is designed by engineers on such projects as highway jobs; in some cases, such as private and commercial work, her company assists in creating a seeding plan.
“First of all, what is the site? Is it a lawn? A field? Is it a golf course, a meadow? Is it a temporary stabilization?” she says.
“The second thing we would look at is the use. Then we would get into things like traffic and deep root systems, and then we would look at things like maintenance. Does it require irrigation? Is it going to require constant maintenance?
“We would put all of those things together to come up with something specific for that individual site.”
But in some cases, erosion control companies must abide by seed selections that are already specified, as in the case of government-funded projects.
Roger Taylor, co-owner of Greenstate, a company based in southeastern North Carolina, will sometimes choose the seed mix for customers, but his company does a lot of work for the US Army Corps of Engineers, which provides its own seed specifications. Taylor’s company uses North American Green’s products, including the company’s cotton fiber–reinforced hydromulch, HydraCX2.
And abiding by specifications is also the case for EQR in Arbutus, MD, which works on many federal- and state-funded projects, says Rick Scaffidi, vice president. For most of these jobs, the seeds have been selected through the specification process.
“A problem we have from a contractual standpoint is that a plan set will have to go through multiple permit processes, and sediment and erosion control is a separate agency, typically a local component of a region,” he says.
“Seeding many times goes through the sediment and erosion control plan sets, both temporary and permanent. It’s not always the case—sometimes a state environmental agency such as the Maryland Department of the Environment or Maryland Department of Natural Resources will review permanent seed mixes—but for the most part, the sediment and erosion control [agency] will review the specifications on a given plan set for their temporary permit’s seed mix.”
Using Native Seed
It is common these days for erosion control specialists to be asked to use native plants when working a job.
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Photo: Ram-T Corp. |
| Seeding at Avon Grove High School in Pennsylvania |
“There are some counties in Colorado that absolutely refuse to use anything but natives; it’s against the law to use anything that’s considered an introduced species,” says Dean. “We are pretty much governed by native species.
“Some municipalities are more interested in getting vigorous growth and sometimes species get introduced, but generally speaking, when we are involved in the design or the build of it, we prefer to use those things native to the area.”
What constitutes native? The term is sometimes defined as plants similar to the indigenous vegetation or plants that come from seed that has been gathered from the geographical location in which a job is done.
American Civil Constructors does a lot of work for the Federal Highway Administration. On one road project, the US Department of Agriculture’s Forest Service restricted the company to using plants that could be collected in the six states contiguous to Colorado at an elevation of 10,000 feet or higher.
“Sometimes that causes problems. Not a lot of seed is grown at those kinds of altitudes because it doesn’t produce as well so that you can get a crop out of it,” Dean points out. “We actually had to trace one seed source from Wyoming back to the state of Washington, but the family and the plant’s originator actually came from Wyoming, even though it was currently being produced in Washington.”
Ram-T often gets requests to use only native plant species whenever the project involves wetlands or reforestation work.
Scaffidi of EQR says his company is almost always asked to use native plantings, with the exception of temporary seed mixes. His company’s work is focused on streambanks, wetlands, and bioretention facilities, and nearly all of them use the native mix.
“Every once in awhile we have to use material that has to come from a specific locale,” he says. “Part of the problem in doing something like that is that you have to go through the entire planning process in order to see if that works or not, because that requires somebody who’s designing the project to know and understand who is collecting seeds from that area and can make that seed available at the time of the construction phase of the project.”
Sometimes the design phase occurs a few years before the construction phase, and the project might be designed by a group that is outside of the region.
“They have to understand what would be available in that particular area at the time of construction,” notes Scaffidi. “Sometimes, it’s just too hard to coordinate. While it’s ideal from an ecological standpoint, from a practical standpoint, it’s very difficult to do.”
Taylor rarely gets requests to use only native plant species on a project. He believes the reason he doesn’t get more requests for natives is because of a lack of awareness about their benefits.
Presently, he’s working a lot with wildflower mixes. “The wildflower helps on maintenance in the long term,” he points out. “We’re going to make sure we have the annuals and perennials seed with it. The jury is still out—we haven’t seen the results long enough now to say whether that’s going to be the thing to do or not in the future.
“So much of the time, you’ve got to worry about the maintenance and the water, and we’re in such a drought like most of the country, and that has to factor in as well.”
To Amend or Not
As for soil amendment preferences, that can spark a “very, very heavy debate,” Dean says.
“The topic of soil amendment is one that is fraught with a lot of peril, because the experts have different opinions,” he says. “If you really want to alter the soil tilt and structure, you need to amend with some kind of compost or soil additive that either adds to the sandy soil or breaks down the heavy clay soils.
“The obvious drawback is that you have a potential weed-seed infestation anytime you use something that comes out of a cow or from somebody’s yard in sweepings or grass clippings,” he adds. “It’s supposed to be heated to a certain degree, but typically you’re going to get some weed from a compost additive.”
Dean prefers to use additives such as Biosol organic fertilizers. “It’s absolutely weed-free,” he notes. “But it does not have the capability of altering the soil condition as a compost would. After a project has been built, the topsoil either has been stockpiled or scraped up from somewhere else and is devoid of any of the little creatures that help make topsoil what it is. Biosol is a way to encourage those kinds of growths that will ultimately result in a fertile topsoil that will sustain life.”
Another product Dean’s company uses is Humate, which is humic and fulvic acids, raw material extracted from the soil.
“We try to create a situation that gives the grass plants the most chance of survival in an area where previously we’ve had problems getting things to grow because we were missing a piece of the necessary micronutrients,” Dean says.
Many factors come into play when choosing soil amendments: climate, season, and site conditions such as steep slopes versus flat ground.
“If you can get tractors and that kind of equipment on a parcel, that lends itself to one sort of soil amendment,” Dean says. “Compost is very difficult to apply on extremely steep, rocky slopes. In that case, you’d be better off with something else.
“In the case of Guanella Pass, where we were doing some work, it was absolutely forbidden that we bring any introduced species to that high-altitude pass, so compost was not a choice up there,” he says. “Humate and Biosol were the recommended soil amendments. So another factor that may dictate a soil amendment is it being a very sensitive natural area.”
Scaffidi agrees that many factors are involved in soil amendment selection.
“One of the interesting parts about doing work in this region is that there are many different soil types and regions where you do things differently depending on the soil type, groundwater conditions, and a number of other factors, such as organic content within a given area,” he says.
“Many times, if you are working with parent soils, you want to restrict the amount of fertilizer going on a particular site because nitrogen and phosphorus tend to cause other problems or may help in germination of invasive species problems.”
Sometimes his company has to experiment with fertility rates on a given type of existing soil and combine it with information about a site “to see if we can manage the nutrients on a particular project better so that we can have good germination rates for the type of seed we’re applying but don’t cause any other problems with invasive species management issues,” says Scaffidi.
Case in point: phosphorus.
“There are sites where phosphorus levels are so high you can’t do anything about it, and there’s usually no need to add any phosphorus, but it’s not as much of an issue if you end up adding some according to a standard specification.
“But there are areas where you’re trying to reduce the phosphorus loading so you can get it down to a very small percentage of available phosphorus and not trigger any invasive species problems. That’s a concern when you are by water areas, stormwater management areas, or bioretention areas, so it becomes a management issue. Sometimes you have to change your seed mix a little bit,” he says.
The use of soil amendments depends strictly on the soil rather than the condition of the landscape, Turner notes. “What does the soil need in order to grow whatever it is you are trying to grow? It really has very little to do with the conditions.”
When it comes to choosing amendments, “If a test is not required or if there’s no time allowed, we always put down starter fertilizer, lime, fiber mulch, and tackifier, and in some areas, if it’s in the summer, we may put down wetter enhancers—soluble gels that contain and release water,” she says.
“Soil tests are also a way we would determine what we would need to add to the soil in the way of organics, fertilizer, and lime.”
Ram-T also uses Earth Chem’s soil stabilization polymers in its projects to hold mulch in place.
Timing and Method
One approach to seeding is to stagger the planting schedule as to achieve ground cover quickly and then to introduce slower-growing, longer-lasting species.
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Photo: Ram-T Corp. |
| Terrain often determines which application process to use. |
“With the exception of some mining companies, we will plant Milo, which will establish itself very quickly, and then at a later time reseed with whatever mix the owner wants to use, using the prior planted stuff as growing mulch, if you will,” says Dean.
Scaffidi says it’s possible to stagger the planting schedule “if you have an open area where you can initially use a temporary seed mix and then go back with the permanent in a better time of year, depending on what you are trying to seed.
“But sometimes you have to be careful of how you’re initially stabilizing and if there is a way to get this permanent seed mix integrated with enough soil contact in order to germinate properly,” he adds. “There are issues you have to be careful of when you’re staggering any type of seeding operation.”
He says another problem with many areas is a significant amount of runoff, which might necessitate matting. A project involving a steep slope will require matting over the seed, he says.
“Obviously, you can’t throw seed on top of the matting, so you’re fixed to putting your permanent seed mix down and then placing the matting on top of it. There are certain restrictions you have to follow because of the construction, the seed mix, and the type of materials you use.”
Ram-T applies all of its seed at once, Turner says.
“We don’t do anything layered—the type of work we do is not a long process but one mobilization and then maybe some repeat maintenance work,” she says.
Like many companies, Ram-T is relying on a variety of application methods to get its work done. Most of the time, the type of equipment used depends on terrain.
“We do it all: We do hydroseeding with different kinds of binders, broadcast seeding, box seeding,” says Turner.
American Civil Constructors has also used a variety of methods to apply seed.
“We use them all, and we’ve made up some,” says Dean. “To the extent that big projects demand big application rates, we’ve done everything from spreading seed with helicopters to hydroseeding equipment to tractor-mounted spreaders, as well as a combination of these. It’s the terrain that dictates what kind of equipment you can best use.”
Taylor hydroseeds about 80% of the time. The factors dictating his choice of application process also center primarily on terrain.
“We’ve got some areas with high erosion problems,” he notes. “I want to use a lot of turf reinforcement mat.”
There is also a great deal of development going on in his area. “Real estate is a hot commodity; they’re sticking houses on every piece of land they can get them on,” Taylor says. “Sometimes, it’s not practical for me to try to drag 400 feet of hose to where I need to get it seeded. In cases like that, I would just seed it conventionally.”
EQR uses a combination of seed application methods according to what’s needed.
“Most of the time we broadcast, because we are in areas where you can’t get a hydroseeding machine in,” Scaffidi says. “In those areas where we can get a hydroseeding application, we do. Or I can get a small tank out to a given area.
“But when you are doing a very large wetland, it’s difficult to hydroseed. You have to be careful that many of the materials you use, such as tackifiers, are going to hold up during storm events because the wetlands are there to get wet, so if it’s wet all the time, some of the tackifiers don’t work properly.
“If it floods, sometimes you determine seeding methods in order to keep everything in place until it germinates, since the seed will float on you,” he adds. “Or you might have to incorporate the seed rather than hydroseed or broadcast.”
Seeding From the Air
Skyline Reclamation in Fairview, UT, recently conducted a an air-based steep soil stabilization job for Williams Gas in 30 acres of high country of western Colorado.
Skyline used a twin-rotor Kaman KMAX to do the work, which included covering 3,000 vertical feet of slopes steeper than 1:1, utilizing Canfor’s EcoFlex Flexible Control Medium.
The application protected a newly constructed gas pipeline. And while air application wasn’t the only option for spreading the seed, it was the best one, says Bill Lee, Skyline’s president.
He says about three seed mixes had been specified for the job. “This was a very steep slope, and it was a southern exposure, so we came up with a seed mix of about 10 types that we thought would work. It was approved by Williams Gas,” he says.
Lee says he’s used Canfor’s products “almost exclusively. We’ve been really happy with the quality for years, and we’ve been doing this for about 13 years. The EcoFlex worked great. Williams Gas was extremely pleased. It tied that hillside together. We put it on at 2,700 pounds to the acre. We ended up putting a little more on than we anticipated.”
Ensuring Quality
Thanks to strict measures enacted by many states, those choosing seed don’t have to worry as much about the integrity of the seed supply and avoiding weeds that may slip into a mix.
“Colorado has very strict seed laws, and our suppliers have to follow those,” says Dean. “All of the seed has to be tested usually within six months of being used. It’s tested for weed content and germ purity,” says Dean.
The PLS designation—pure live seed—addresses such issues as chaff, mouse droppings, or any other material that is not seed and helps companies choose seed that will ultimately germinate and grow.
“Some states require you send in seed samples to the agricultural department,” says Scaffidi. “They will test prior to your receiving the seed, and if they OK the seed, then you can continue with the order and use that seed for a particular area.”
Scaffidi says Virginia has one of the toughest standards in the region. Maryland does random testing.
Skyline Reclamation ensures the quality of its seed supply by buying it from supply houses that have annual quality checks on the seed. Sometimes, the project requires a seed test onsite.
Taylor says to ensure the quality of his seed supply, he refuses to cut quality by buying cheap. “I want high germination and low weeds,” he says.
Seeding companies often have to coordinate planting efforts with construction schedules. The possibility exists that a delayed construction schedule might change plant selection because of later-season planting.
“There are obvious seasons you prefer to seed in,” says Dean. “By far, fall and late fall are the preferred seasons in the Rocky Mountains. We do a lot of dormant seeding—nothing is expected to come up until the following spring.”
Another preferred season is spring, before mid-June. The reason, Dean says, “is because all of a sudden our springtime leaves, and we get hit with this long, hot summer. Even if you do get seed up, generally it fries, so that’s not the optimum condition to be in,” he says.
There are, however, places in the high mountains where seeding can take place during the heat of summer.
“Rather than having different choices of plant materials or seed selections, generally what happens is in the cases of seed application, they will suspend time on the contract until such time as we can get in and start seeding again,” Dean says. “The seeding dates and optimum times for seeding often drive the schedule.
“Sometimes it’s the other way around, and they say they have to proceed. If need be, they’ll pay us to come back and do the seeding again.”
The preferred planting schedule depends on the type of seed being used, Scaffidi notes. “There are different mixes for each time of the year. In winter, we use one type of mix, another in springtime, another in fall. You’ll get that variation within a permanent seed mix.
“One of the things that has been a problem in the industry has been that a permanent seed mix is usually a perennial seed mix, and it does not germinate as quickly as the temporary seed mixes,” he adds.
Many times, regulations require EQR to finish a part of a project as it’s being constructed. “On the smaller stream applications, you have to button up everything at the end of each night or within a short window of two or three days, and you go right from the construction to a permanent seed mix,” says Scaffidi.
“Sometimes you have to modify the permanent seed mix so there is temporary seed germination and stabilization in a short period of time. We have to work with the agencies in order to accommodate those modifications, because if you just go to a permanent seed mix, it may not germinate for one to three months, depending on the time of year.”
Designers, engineers, and ecologists are trying to come up with a plant set that meets the requirements on the particular job, as well as meets the regulatory requirements of that state or locale, Scaffidi says.
“They typically will initially put together a seed mix. The problem we have from a construction standpoint is that the seed mix may or may not be available during the time the construction occurs,” he says.
If a construction schedule is being held up, necessitating a different plant selection because of a later-season planting, most plant replacements have to go through the agencies again for their approval, Scaffidi notes.
“That way, they can monitor and manage good species selections for a given area,” he notes. “Different local jurisdictions will have different levels of expertise, so sometimes we can offer a lot of expertise in helping them choose the type of replacement seeds. We work with the different agencies for any replacement, depending on the time of year or weather conditions that might dictate a different seed.”
Turner says her company will ask contractors to allow Ram-T participation in a decision regarding construction delays “because we want them to get the maximum germination,” she says. “If we are running out of spring and getting into summer, we certainly don’t want to be shooting a bunch of stuff that’s not going to come up.”
Dean says service to the property owner is also a priority. “If we can help the owner achieve something by doing something completely different than what he has specified, then it behooves us to see if we can’t help the owner make the necessary changes to get something where he will have better success,” he says. “Sometimes we are successful and sometimes we’re not, but it is all service-directed. If you’ve got a happy client, that means you’ll have a client for some time to come.”
Carol Brzozowski is a journalist in Coral Springs, FL.
EC - January/February 2008
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