Hydraulic seeding: It's all in the slurry
Gassman, Hydro Turf Planters Association
As in - Grounds Maintenance,
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
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
Additives for the slurry
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
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
difference between paper and wood mulch comes into play with the
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.
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.
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 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
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
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,
(HTPA closed down November 2004), and
is the owner of Fairway Greens Landscape Services