Variables in Hydroseeding

Nov. 1, 2002

Hydroseeding has been a landscape practice long enough that some states have developed a voluntary certification program. Contractors refer to it as “simple” and “basic.” Still, going onto a supplier’s Web site is enough to confuse a seasoned landscaper. If it’s so basic, why so many choices? This article focuses on the variables in hydroseeding projects in various parts of the country and how those differences might alter choices that hydroseeding professionals make.

Many things, of course, depend on the project. Gone are the days when hydraulic seeders were spraying only residential lawns or the occasional golf course. The modern-day hydroseeding professional has a plethora of job types for which to prepare. Seed suppliers have wildlife mixes for wetland seeding. Wildflowers are spread along roadsides, and native seeds are used for steep and rocky reclamation projects. Selecting the correct seed, even for the simplest project, is imperative for success.

That said, what other variables might affect the success of a hydroseeding project? Any horticulturist knows about the United States Department of Agriculture (USDA) zones. But can hydraulic seeders take a rocky, clod-ridden, baked clay soil and, with no preparation, simply spray on a grass mix and create a lawn straight out of the magazines? Possibly in the short term, but what happens when the roots grow out beyond the mulch? Is hydroseeding best done in the spring or fall–with or without accessible irrigation?

To create a successful project, all of these variables have to be adjusted for each particular region. Similar to any other agricultural profession, planning and preparation are the keys to success. Choosing correct seed, knowing the USDA zone, preparing a good seedbed, and having the right equipment for the job and the right fertilizers and amendments will not only ensure a temporary greening but will provide a foundation for a lasting lawn or meadow.

Basic Seed Selection

Cool-Season Grasses

Generally turfgrasses can be divided into two main categories according to the area where they thrive best. Cool-season grasses will grow well in northern climates. They will withstand colder winters, but tend to suffer in areas with hot and dry summers. Therefore, they do need a lot of water in the hottest days of summer. These grasses perform their best in areas where marine influences alleviate scorching summer heat.

The cool-season grasses for residential lawns or other turf uses are planted either singly or in combination blends. They perform well enough on their own to create a lush single-grass lawn to the customer’s specifications. Whether clients want a soft, fine-bladed lawn or a rougher-textured grass for a playground, the cool-season grasses can provide the uniformity desired. The problem with a lawn where one grass type dominates, of course, is the Irish potato famine phenomenon. With a monoculture, one disease or pest can wipe out the entire project, costing the customer time, money, and great dissatisfaction. Blends that contain two, three, or sometimes four types of grasses are safer and provide better greening from spring through fall. Additionally, when weeds need to be sprayed out, reseeding grows back quicker with a blend. When dealing with demanding customers, remember to educate them about whatever type of lawn seed they will be caring for. Most grass seed will germinate, but whether it creates that lush, deep green lawn will depend on the environment in which it’s planted and the care it receives later.

The primary cool-season grasses include the bent grasses, fine and coarse fescues, bluegrasses, rye grasses, and redtop. Clover often is included in lawn blends because it is believed to provide nitrogen and gives a certain ambiance to a nice lawn. Many homeowners enjoy white clover.

Warm-Season/Subtropical Grasses

Just the opposite of the cool-season grasses, subtropicals grow robustly in hot weather and will go dormant in cool weather or winters. When they go dormant, they become like straw. To keep lawns green during these times, they can be overseeded with the cool-season redtop, bents, fine fescues, or bluegrass. The most common warm-season grass that is hydroseeded is Bermuda, but zoysia grass and buffalo grass also are common, depending on the region. Many Bermuda varieties are available, depending on the project needs.

The quality that makes Bermuda ideal for hydroseeding in the south is its ability to knit runners aggressively into the soil surface. Although Bermudas will stay green longer than many warm-season grasses, they still brown out during a heavy frost. They all require sunny locations and must be thatched to look their best. Mowing should be as low as possible–down to half an inch.

Another warm-season seed used for lawns in Arizona is the AZ 1–Kikuyu grass. Carson Carroll, with B.C. Hydroseeding in Mesa, uses this grass when customers want a wider, coarser-bladed grass. Carroll says an added benefit is that the seeds and pollen are belowground; because of this, people who have allergies to other grasses tend to request it.

To get even more specific about seed selection, each region has different grasses native to its climate (discussed in the US Virgin Islands [USVI] case study). In the USVI, Bermuda, Bahia, and zoysia grasses are considered native grasses and used on new construction sites. Landscapers there mix the native grasses with annual cool-season grasses such as rye and fescue to get a fast, temporary cover and shade for the perennial grass.

Other grasses used in the USVI include Bahia, buffel, and hurricane grasses. Bahia is a low-growing perennial that spreads by short, heavy runners. It requires lower maintenance and is drought-tolerant. Bahia is fairly free from pests but will not tolerate alkaline soils. Buffel grass is a warm-season, leafy bunch grass that forms knotty crowns and a mass of long, rhizomatous roots that can reach a depth of 8 ft. Because of the massive root system, its erosion control qualities are unsurpassed. It establishes easily, is drought-resistant, and produces ample amounts of forage. It grows best in sand and medium-textured soils and also performs well in low-rainfall areas.

Hurricane grass is the most prevalent turfgrass in the Virgin Islands. It is hardy and aggressive and stands up to wear and traffic. The densely thatched grass is drought-, salt-, disease-, and insect-resistant. For the area, it’s an excellent lawn grass; the only drawback is that it needs frequent mowing to keep seed heads removed.

Seedbed Preparation

Landscape contractors know the value of a good seedbed when planting new lawns and flowerbeds. In hydroseeded jobs, there are a few areas that are too rugged to prepare a good seedbed in the traditional way. Mulch suppliers, such as Conwed Fibers, address that problem with niche products that keep the seed bonded inside a chemically bonded fiber matrix until vegetative growth stabilizes (see the Fort Bliss case study mentioned later). For golf courses or residential lawns, however, seedbed preparation still should be an important part of the job plan. If customers pay for a hydroseeded lawn hoping for one straight out of the magazines but instead get a temporary lawn that never truly takes root, they certainly will get the word out about their dissatisfaction. Taking the extra time to get it right by preparing a good seedbed will pay off greatly for contractors in the long run.

Seedbed preparation is especially important in areas where pH is either too high or too low. Because that includes most of the country, the first thing that should be done on a project is a soil test. If the pH is below 5.5, indicating an acidic soil, lime should be incorporated into the topsoil. Some hydroseeding professionals add lime into their mix and apply it with the seed and mulch material. According to Nash Hardy of Hardy Landscapes Inc. in North Carolina, adding liquid dolomite lime to the mix is not a bad idea. But, he notes, it doesn’t take the place of tilling the lime into a good seedbed.

“Typically our soil pH is around 4.3 to 5.2,” Hardy states. “With hydroseeding–which is increasing a lot in our area–the lime [in the mix] binds only to the top quarter or half inch of the soil. It doesn’t move through the soil profile.

Grass might grow initially, but when the roots grow down into the untreated soil, it just dies.”

On the opposite end of the spectrum is a pH of 8.0 or higher. Most soils west of Nebraska fall into this category in one way or another. Dale Stukenholtz, Ph.D., consulting agronomist and owner of Stukenholtz Laboratory Inc. in Twin Falls, ID, describes these soils as characteristic of areas with little rainfall. He explains the soil tests and how to solve the problems found with these soils. “These soils are either alkaline or alkali,” he points out. “Alkaline soils have an excess of lime, and alkali indicates there is too much sodium present.”

If a soil test indicates the soil is alkaline, then the remedy is to add sulfur, advises Stukenholtz. Most of these soils also need a good supply of micronutrients, especially lots of iron. In the case of alkali soils, which occur in such areas as Colorado, addition of sulfur will correct the sodium problem. When contractors are working on new residential lots, remnants of gypsum sheetrock often are left over. In areas with a sodium problem, homeowners simply can break it up and put it in their flowerbeds. Stukenholtz says some places actually recover the materials and shred them for landscapers.

Once soils tests and amendments have been taken care of, seedbed preparation should proceed the same as other lawn installations. It would be hard to add too much nitrogen to a newly seeded lawn, no matter how it’s installed. Phosphorus doesn’t move much in the soil, so if a soil test shows that it’s needed, it should be worked into the top 3 in. so roots can get to it as soon as possible.

The amount of seedbed preparation that hydroseeding professionals do is wide-ranging. Some simply advise the homeowners how to prepare their lot prior to hydroseeding. Others figure the cost of seedbed preparation into their budget for the job. In North Carolina, for example, costs range from 2 to 3 cents/ft.2 with no seedbed preparation, up to 5 cents/ft.2 with preparation. Hardy Landscape bids in the 5-cent range but includes cultivation, leveling, and soil amendments with the job. Contractors should at least explain the differences in technique for the different regions and allow customers to decide what method they want to go with.

Educating customers about caring for their new lawns is especially important in drier regions, such as the Southwestern US. Carroll notes that in Arizona, where the terrain is fairly flat, moisture is the primary concern.

“The one thing that is a big problem here is getting people to keep the mulch wet enough so that the seed will have the chance to germinate,” Carroll relates. “I use all kinds of seeds, depending on the needs of the family.”

Hydroseeding in the USVI

Education and promotion of hydroseeding was the driving force behind the Virgin Islands Hydroseeding Demonstration Project initiated in 1996. Agencies on USVI applied for and received a grant from the Coastal Services Center to conduct workshops on hydroseeding and to seed roadsides and slopes threatened by erosion. The workshops were developed and conducted by the Virgin Islands Department of Planning and Natural Resources (DPNR), Coastal Zone Management Program, the Virgin Islands Department of Public Works—Environment Services Division, the University of the Virgin Islands Cooperative Extension Service (UVI-CES), and the Virgin Islands Conservation District, with assistance from the USDA Natural Resources Conservation Service.

The cooperative agencies identified one of the primary nonpoint-source pollutants as being sediment that is eroded from construction sites, unpaved roads, driveways, parking areas, and other disturbed soils. USVI has shallow, clayey soils and steep or rolling slopes and, because of the small size of the islands, erosion and runoff into beaches is inevitable. Any given construction site is in close proximity to beaches and therefore to marine resources and the coral reefs of the islands. Quite literally, sediment is degrading the USVI coral reef systems because of development, and there is an “urgent need” to get disturbed soils revegetated as quickly as possible, according to UVI.

Before the demonstration project, hydroseeding was used on a very limited basis, mostly because of inaccessibility to the equipment and to necessary products. Additionally, high transportation costs and limited knowledge restricted the use of this erosion control practice.

The grant money allowed the purchase of hydroseeding equipment for two primary projects. On one project, demonstrations were presented at hydroseeding workshops held at UVI. The other part of the grant was to seed roadsides and slopes that were in ruin from erosion. Julie Wright, a natural resources specialist with UVI-CES, reports that the interest in the hydroseeding equipment was so high that UVI developed a certification workshop and equipment operation policy for equipment use.

“Two Turbo Turf 750 machines were purchased by DPNR using a grant from the NOAA [National Oceanic and Atmospheric Association] Coastal Services Center to evaluate and demonstrate effectiveness of hydroseeding in the Virgin Islands. UVI-CES was a partner on that grant and provided education and outreach on the project,” Wright explains. “When the grant was completed, DPNR turned the equipment over to UVI-CES to conduct training workshops and rent out locally to promote use of the practice.”

The hydroseeding machines DPNR purchased have 750-gal. tanks with 100-ft. hoses that can seed approximately 10,000 ft.3 per load. The rental fees from the 319 grant, a nonpoint-source management grant from DPNR, go to help purchase equipment replacement parts for the machines and for materials used during presentations at the workshops. The main demonstration workshop was set up in May 1996. Workshop participants were able to observe seeding of disturbed areas of both university campuses, located at St. Thomas and St. Croix. Fifty-seven people attended the first workshop.

In a later stage of the demonstration project, the goal was to make the hydroseeding equipment available to the public and to other agencies for rental to promote hydroseeding on the Islands. UVI-CES developed an operational policy that describes and outlines proper procedures to be used for borrowing, using, and returning the equipment. By June 1997 the first Hydroseeding Certification Training Workshop was held for St. Thomas and St. John Districts. Another was held at St. Croix District in January 1998. Forty-three contractors, architects, engineers, draftsmen, and government agency representatives have taken the workshop, received hydroseeding machine manuals, passed the certification exam, and received their Hydroseeding Certificate of Training cards.

Wright admits there was no real magic to deciding which seeds to use for the projects. Native naturalized perennial grass species were used for the construction sites (Bermuda, Bahia, and zoysia), and rye and fescue were mixed in to provide a fast temporary cover. Mulch was selected based on manufacturers’ recommendations and what was available through local distributors.

Wright identifies acceptance of the practice within the construction industry and maintenance of the hydroseeded areas as the main challenges with the Hydroseeding Demonstration Project. “Basically, convincing the contractors that temporary seeding of bare sites is a good idea and not just a waste of money [was a challenge],” she remarks. “And now that contractors on St. Thomas are using the practice, maintenance appears to be a big challenge, especially keeping the seeded area watered to ensure good germination of both annual and perennial grasses.”

Wright adds that birds in the Virgin Islands love hydroseeded areas and feel free to graze the areas like a buffet. Covering the areas with mats helps, but she notes that hydromulch offers no help in deterring their appetites.

All in all, the Virgin Islands Hydroseeding Project has grown to be a success. In addition to the university sites hydroseeded in the demonstration, roadsides on St. Thomas and St. Croix have been hydroseeded, along with a drainageway and a portion of the Anguilla Landfill on St. Croix (see sidebar for update).

Fort Bliss Hydroseeds Small Arms Ranges

At the Army installation at Fort Bliss, TX, rainfall estimates average between 8 and 13 in./yr. The small arms training qualification ranges receive around 8 in. and are considered to be in a desert basin terrain with a semiarid climate. Wind and water erosion has been deteriorating the weapon safety berms and, explains Lieutenant Colonel Rick Gatewood, this increases safety hazards on the ranges: A shooter’s visibility is reduced by sand blowing across the weapons range.

To provide revegetation for the berms, Fort Bliss decided on the use of both erosion control blankets (ECBs) and hydroseeding. The objective of the project was to establish vegetative cover to reduce the erosion as soon as possible. Because of the extreme winds, the berms are slow to revegetate, but with seed and temporary covering, Gatewood believes they should be able to accelerate the process and reduce the wind-borne sediment on the berms.

A native grass to the area, commonly called sand dropseed (Sporobolus cryptandrus), was used in the ECB and the hydroseeding projects. Because the ECBs are so labor-intensive with the necessary soil-to-ECB contact, they were only used in areas with sparse vegetation cover. Hydroseeding was used in heavier canopy areas. The objective in the hydroseeding project, according to Gatewood, was to achieve a canopy equal to that provided by the ECBs. The hydroseed mixture used at Fort Bliss comprised a bonded fiber matrix, fertilizer, and seed. Soldiers used a Reinco Hydrograsser for the berms.

The end impression is that hydroseeding is “a great timesaver and can put down cover quicker and easier than installing ECBs.” Gatewood adds that, when funds are made available, Fort Bliss plans to hydroseed all the ranges to prevent the wind and water erosion that occurs there.