Hydraulic seeding: It's all in the slurry

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By Sean Gassman, Hydro Turf Planters Association

As in - Grounds Maintenance, Aug 1, 2001

Rapid growth after World War II created the need for an easy method of grass establishment for the new highways and buildings being built around the United States. Several processes were tried, but it was not until 1953 that Charles Finn, of the Finn Equipment Co., created the first commercially available hydraulic seeder. Other manufacturers soon followed with similar equipment. The initial process consisted of water, fertilizer and seed. This usually was capped with straw. Thus, hydraulic seeding, or “hydroseeding,” was born.

Over time, various mulches were developed to be added to the mix, with the aim of creating a one-step process using a homogeneous slurry of material. Several types of mulch, derived from paper, wood, magazines, paper-mill sludge and cardboard, have been used, but paper and wood are the two most common today.

The addition of mulch in the hydroseeding process produces a better environment for the seeds to grow. The slurry creates a “micro-greenhouse,” better water retention, resistance to erosion and does not introduce undesirable seed, as can happen when capping with straw. The ability to custom blend a slurry for each job, apply the slurry evenly over an area, producing rapid and uniform germination, gives hydroseeding certain advantages over other forms of turf establishment.

For years, contractors have debated the type and thickness of mulch that provides the best results. The term hydromulching arose from these debates. During the recession of the early 1980s, price wars prompted some contractors to cut their mulch rates to keep material costs low. This produced poor results and eroded confidence in the hydraulic seeding process. The term “hydromulching” soon became prevalent to emphasize the importance of using an adequate amount of mulch. A common definition stipulated 1,500 pounds per acre (or more) of mulch to qualify as hydromulching.

In some parts of the country (particularly those that did not experience this type of situation) “hydroseeding” is the term used regardless of the amount of mulch used. (“Hydraulic seeding” is perhaps a more proper generic term. “Hydroseeding” is more commonly used, but is actually derived from Finn's trademarked name of “Hydro Seeder.”)

Additives for the slurry
The field of hydroseeding has evolved significantly since the 1950s. Now, many products are available to the contractor that can be added to the slurry. Each product is designed to increase the success rate of hydroseeding.

However, mulch is still the most important component in the slurry. Without mulch, the process is little better than broadcast seeding. With mulch, it is possible to create a near-perfect growing environment for rapid turf establishment. The two main types of mulch — wood and paper — can be used alone or together. Paper, while less expensive on a weight basis, can require 20 to 40 percent more material to achieve the same uniformity of coverage as wood.

Regardless of which you use, it's important to apply at least 1,500 pounds per acre to produce good results. At lower rates, the seed bed has little protection and is exposed to the possibility of erosion or even a total wash out. Erosion and wash out can result from storms or over-zealous customers applying excessive water.

It's vital to remember that using adequate mulch is not merely for the customer's benefit. If establishment fails due to low mulch rates, the contractor may be required to perform a respray to produce the desired stand of grass. This will greatly increase your job costs and tie up your crews' time.

The season, location and type of seed also play a role in the application rate. At favorable, cooler times of the year, a relatively low application rate may suffice for planting cool-season turf, due the rapid establishment of the grass and relatively slow evaporation of water during this time of the year. Warm-season grass will take longer to establish in cooler months. Thus, low mulch rates during these times will almost always result in erosion, weeds and a poor stand of turf.

Wood vs. paper
The difference between paper and wood mulch comes into play with the addition of tackifiers. Tackifiers aid in the bonding and holding ability of mulches, creating a fiber-to-fiber-to-soil bond. When tackifiers are added to paper, the application rate must be 1,500 pounds or less per acre. At higher mulch rates — 2,000 pounds or more — ”paper maché” can form with paper mulches, reducing air flow and moisture available to the seed. This can result in large areas with thin or nonexistent turf establishment. Newer synthetic fibers added to paper mulch increase bonding with soils and reduce ”paper maché substantially.

Wood mulches with a tackifier do not bond as tightly as paper. Therefore, air flow and water is not cut off from the seed. Even at rates as high as 3,000 pounds per acre, wood mulch with tackifier will not have a negative impact on turf establishment. At these rates, erosion is easily controlled and the threat of a total wash out is almost completely eliminated. With the increase in the thickness of the mulch, its water holding capacity is much higher, and the seed has the greatest chance of survival. Synthetic fibers may also be added to wood mixes to increase erosion control.

Tackifiers
Two types of tackifiers are currently available: organic and polyacrylamide polymers. Organic tackifiers are the least expensive and are usually made from guar gum or plantago. Organic tackifiers are best for flat to moderate slopes. Their holding ability and effective longevity is determined by the quantity you add to the slurry. Usually viewed as short-lived, organic tackifiers are appropriate during the turf's active growing season.

Polyacrylamide tackifiers last longer, and at lower application rates will produce the same holding ability of organic tackifiers. Polyacrylamide, with synthetic fibers in the mix, is used in Bonded Fiber Matrix (BFM) products due to its ability to hold extreme slopes. With greater holding abilities in smaller quantities, polyacrylamide is often preferred when space on trucks is limited.

Not all polyacrylamide is the same. Different particle sizes are appropriate for different uses. Larger-particle polyacrylamide is popular for its ability to hold up to 400 times its own weight in water. Used in the nursery and landscape industries as soil amendments for years, it has now found its way into hydraulic seeding slurries. With this material added to the soil and the hydroseeding slurry, water requirements can be reduced. Some claim as much as 50 percent less water may be needed to establish the turf when polyacrylamide is used. Thus, it may be a valuable tool in areas with drought conditions and water rationing.

Some contractors combine organic and polyacrylamide tackifiers in the hydroseeding mix with excellent results. Tackifiers not only aid in bonding the application, they also “slick up” the slurry, reducing or eliminating clogs in hoses.

Fertilizer
Most hydroseeding jobs are applied on a site where the soil nutrients may be less than desirable. Liquid, soluble starter fertilizers are frequently added to the slurry for immediate availability of nutrients. Working with these and traditional slow-release granular fertilizers applied before or after hydroseeding can result in a superior, sustained stand of grass.

Other additives
Many other additives are directed at the poor soil that most hydroseeding is performed on. Humic acid, lime, sea weed extracts, vitamins, plant extracts, polyhydroxy acid, enzymes and other materials are available for slurry mixtures. The agronomic value of some of these materials is debatable (and a subject for another article), but be aware that they are available for use if you so desire.

Contractors sometimes add materials to the slurry that have not been specially formulated for such use. For example, when native grasses or wild-flowers are needed, soil contact is a must. Some contractors have successfully added soil to the slurry. Another example: manure and cotton seed meal have been added instead of granular fertilizer.

The seed itself, ironically, is one thing in a slurry that you pay relatively little attention to. But do not neglect proper seeding rates.

Too little seed will result in a thin stand, of course. However, avoid the temptation to add too much seed to produce an “instant lawn.” This can increase competition, resulting in grass plants that are spindly and weak. Such plants have trouble penetrating the mulch and will struggle to become well-established. Competition also results in poor root development. Consequently, you'll see winterkill of warm-season turfgrasses, and summerkill of cool-season species, both as a result of shallow root systems. For these reasons, make sure you use no more than recommended seeding rates, or even slightly little less.

Knowledge makes the difference
If you're looking to get into the hydroseeding business, the first step is to learn about the process. Knowledge will save you money and headaches, and keep you out of legal trouble. Research proper techniques, turfgrasses, soils, etc. Good agronomic knowledge of turfgrass culture will allow you to make proper decisions about additives.

When looking at equipment, ask for a demonstration. Make sure salesmen back up their claims of what the machine will do. Insist on demonstrations with wood and paper, and thick and thin slurries. Make sure the equipment will meet the requirements of any job you're likely to do. Load time, mix time, spray time, quantity of material that you can mix at one time, and spraying out of a long hose, must all be checked out before purchasing equipment.

With the present popularity of hydraulic seeding — partly due to new smaller and less expensive equipment — a flood of contractors are now looking into this industry. Unfortunately, many purchase equipment with limited working knowledge of the machine and even less about hydraulic seeding. Even the newer models are not cheap, so it takes a fair sum of money to get started. You owe it to yourself to do thorough homework before purchasing.

As you're shopping around, you're likely to come across claims of low initial cost with extremely high profit margins. Be warned! Hydraulic seeding can be a profitable business, but good results don't happen automatically. Pushing tanks for maximum coverage with minimum material will result in a poor stand of grass infested with weeds. With such poor results, “hydroseed” can become “hydroweed.”

Unfortunately, in some areas where hydraulic seeding is a well-established trade, price wars, material slashing and “blow-and-go” contractors all have played a role in wounding this industry. As result, jobs often are no longer specified for hydraulic seeding, but sodding instead, because hydraulic seeding has gained a bad reputation. This is mostly due to operators with a lack of knowledge about the process. Price is often the only way of getting jobs when contractor's don't understand the industry.

Every job is different. Evaluate each job site thoroughly before pricing it. You don't always load the tank the same way; you load it to meet the demands of a specific job. What you put in the slurry and on the ground will play a direct role in the success or failure of the application. With higher mulch rates, additives and proper seed rates, hydroseeding produces a stand of grass second to none.

Sean Gassman was the president of the Hydro Turf Planters Association (Dallas, Texas; (HTPA closed down November 2004), and is the owner of Fairway Greens Landscape Services (Garland, Texas).