July 15, 2015 11:26

Hydroseeding: What’s in the Tank?


Hydroseeding is really kind of a magical process, when you think about it. You mix mulch, fertilizer, tackifier, seed and water in your cauldron, wave your wand at a field or hillside, and pretty soon—abracadabra!—it turns green and lush. Magic.

Okay—so maybe, “Harry Potter and the Chamber of Slurry” would not have been a bestseller. And you won’t have Professor Snape’s help in choosing what you’ll include in your potions. There are a number of admittedly non-magical factors you have to consider when deciding what to put in your tank.

Of mulch and machines What you do put in the tank will partially depend on what type of machine it’s attached to. There are two basic types of hydroseeders: gear-driven, mechanical-agitation machines and jet-agitation machines.

Mechanical-agitation machines mix the slurry with paddles. Jet-agitation models use a centrifugal pump for both mixing and spraying. Part of the pump’s output is directed back into the tank via a series of jets; hence, the name.

Your mulch menu consists of wood and paper in various incarnations: pure wood fiber; recycled newspaper/ cellulose; wood/paper blends; and pelletized wood/paper blends called “jet spray.” Additionally, there’s BFM (bonded fiber matrix), which is a wood or wood/paper blend, bonded together by a polymer to form a sprayed-on erosion-control blanket.

There’s also a high-performance hydromulch called FGM (flexible growth medium). It’s composed of long-strand, thermally-processed wood fibers, crimped inter locking fibers, and performance-enhancing additives.

It’s used primarily on severe erosion control jobs.

“A lot of guys, including myself, like to use 100 percent wood,” said Doug Holmgren, owner and president of Turf Blasters, Inc., Sioux Falls, South Dakota. “The long splinters of wood stack up unevenly on top of each other, crisscrossing, creating a net. It breathes better, holds moisture better, and it’s better for erosion control. But it’s a thicker slurry, and for that, you need to have mechanical agitation.”

“A mechanically-agitated machine will handle a little thicker slurry than a jet machine,” agrees Ray Badger, owner and president of Beaver Falls, Pennsylvania-based Turbo Technologies, Inc., a hydroseeder-manufacturing company.

“But it’s not as much difference as some people say, especially if they don’t sell jet machines.”

He says that the most powerful jet machines are almost identical in the mulches they can handle, as compared to a less heavy-duty mechanical machine. You can use a wood/paper blend, or paper, but you can’t use BFM, FGM, or 100- percent wood mulch in a jet machine.

“If you have a jet-agitation machine, then you’re pretty much limited to the paper or cellulose mulches,” says Pete Simmons, mulch division manager at Weberville, Michigan-based Applegate Mulch.

“Wood-fiber mulches don’t work very well in jet-agitation machines,” he said. “They have a tendency to clog the recirculation tubes. A jet has a very limited loading rate. Some owners of jet machines are using wood-fiber mulches, but it’s not recommended.”

Badger says that wood mulch gives seeds better heat protection than paper. “It’s more layered, more like miniaturized straw. Air can move underneath. It’s better for high-heat places like the deep South, Texas and Arizona.”

“Paper mulch is used mainly on flat surfaces,” he continues. “As the terrain slopes, you’ll want to switch to a 100-percent wood-fiber mulch. It’ll stay on better, because the wood fibers are long and narrow, where the paper fibers are larger and kind of round. Also, the paper decomposes a lot faster.”

One caution: paper mulch, if applied too thickly, can form papier-mache,’ prone to flaking or blowing off in sheets. It’s best used for seeding lawns, where erosion control isn’t a concern.

What’s the mix ratio? “The general rule of thumb is 35 pounds of wood mulch to 100 gallons of water,” said James Lincoln, owner of hydroseeder manufacturer Turfmaker Corporation in Rawlett, Texas. “That’s a fairly standard mulch-water density. If you mix your load that way, you’ll have a moderate thickness, and it’s then up to the guy on the end of the hose just how thickly he sprays it.”

David Woehler owns Pittsburgh, Pennsylvania-based Woehler Landscaping, LLC. He does both erosion control and residential and commercial lawn installation. His 750- gallon hydraulically-driven mechanical-agitation machine will cover 11,000 square feet.

“If I’m spraying crown vetch, I’ll put in five to ten pounds of that seed, and 75 pounds of annual rye seed. I’ll use seven 50- pound bales of 70/30 hydromulch—that’s 70 percent recycled sawdust and 30 percent recycled newspaper—tackifier, and a water-soluble startertype fertilizer, a 16-26- 16.”


“With cellulose (paper) mulch, you’ll need to add a tackifier,” says Simmons. “Even on flat areas, if it rains hard enough, the mulch will float.”

Tackifier is the sticky stuff that keeps your slurry, and its seeds, stuck to the surface of the soil. Some hydromulches already contain tackifier. The three main tackifiers are polyacrylamide or PAM, guar and plantago—that’s the material used in fiber laxative. “Originally, ground asphalt was used for tackifier,” says Badger, “which wasn’t very good for the environment or the soil, and it’s been totally eliminated.” PAM and guar are the most popular tackifiers. If you’re in the habit of reading grocery labels, you’re probably familiar with guar. Made from the seeds and leaves of the guar plant, it’s a common thickener used in food processing. “Guar is the traditional old-school tackifier that you used for everything,” says Holmgren. “But because fracking is getting so big, the oil and gas industry has sent the price of guar through the roof.”

PAM has overtaken guar in popularity, largely because of that price surge. A crystallized polymer that absorbs many times its own weight in water, it’s the same absorbent material found in disposable baby diapers. There are some subcategories of PAM, and lots of companies sell it under different brand names.

When water hits the PAM crystals, they swell. “When PAM gets wet and swells up, it’s kind of like Jello,” says Chris Rider, chief technical officer at DirtGlue Enterprises, LLC, a tackifier manufacturer based in Amesbury, Massachusetts. When it stops raining or sprinkling, the substance gradually dries out, releasing the water slowly back into the soil.

For even more stickiness, some contractors add polyester fiber to their slurries. The poly fiber provides a mechanical bond instead of a chemical one, helping tack the hydromulch to the soil with a kind of “grabbing” action.

Seed selection

You can use just about any kind of seed in a hydroseeder. The seed you choose, if it’s not already specified for you, will depend on a number of factors. “I encourage contractors to ask what the intended use of the site will be,” said Dusty Sweat, regional sales manager for Madison, Georgia-based Pennington Seed, Inc. “Is it going to be used for a sports field, a commercial property or a residential development?”

There are however, some grass varieties that aren’t available in seed form; hybrid Bermuda grasses, for example. You have to “sprig” them. You start with sod, rip it apart, and throw the pieces into the machine, or, in parts of the country where Bermuda grass is widely used, you can buy boxes of “sprigs”.

Determining how much water will be needed, and will be available, may be the most crucial factorof all in seed choice. Is the site in arid climate, or one currently in of all in seed choice. Is the site in drought? Will irrigation even be used? The answer to these questions will determine if you’ll need to plant less-thirsty species.

Warm-season Bermuda and Buffalo grasses are drought-tolerant, as well as some natives such as little and big Bluestem. Bahia and Bermuda are thrifty both in price and in water needs. “For the cooler climates, some of the tall fescues and Kentucky bluegrasses have come a long way with their drought tolerance,” Sweat adds.

If erosion control is the main concern, Woehler chooses legumes, such as crown vetch or trefoil. They’ll take nine months to grow, so he mixes in some annual rye to get coverage right away. “There’s a coating on those seeds, so you also have to mix in an inoculant. It takes the coating off, and allows the seeds to get soil contact, so they’ll germinate.”

How do you know if the seed is good? Every bag of seed is required to have a seed tag. It will tell you the purity, how much weed seed might be mixed in, and the germination rate. Use good quality seed from a supplier you trust Most importantly, the seed tag will have the lot number. Every lot is test-grown, and you can ask your supplier to let you see the score a particular lot received. The test data should be available, and you should feel comfortable asking to see it.

“Cheaper is not better,” stresses Sweat. “I always tell contractors, ‘You want this grass to be growing 15 years down the road. Your fertilizer, tackifier and mulch will be gone, but the seed’s descendants should still be there.’ Spend a little extra to invest in long-term sustainability.” In other words, pay for good DNA.


The type and grade of fertilizer you use will depend on what climate and soil conditions you are hydroseeding in. Unless it is in the specifications, ideally, you’ll have the soil tested by a professional lab. Take random samples over the entire site to a depth of at least two inches. The results will tell you your pH and fixed nutrient levels. It should also identify any contamination that might be there.

If you can’t do a test, a starter fertilizer is a good idea. This will help seedlings get established rapidly. Use one with a 1:2:1 NPK (nitrogen/phosphorus/potassium) ratio (15-30-15, for instance), because that’s what growing grass typically contains.

Phosphorus is more important than nitrogen in getting new seedlings established. Two pounds of phosphorus per 1,000 square feet is the recommended measure. Here’s a formula to determine how much total fertilizer you’ll need:

Application rate x area in 1,000s of sq. ft. ÷ nutrient % in the bag = total fertilizer needed.

Holmgren prefers using watersoluble or liquid fertilizers. “I try to stay away from granular. It settles to the bottom of the tank, and by the end, you’re just spraying out white stuff. You can see the little pellets coming out of the gun.”

But Holmgren is an exception. “I suspect that if you were to survey 100 hydroseeding contractors, doing all kinds of different work, 90 of them would be using granular,” said Lincoln.

There are three reasons for this: Simplicity, availability, and cost. Granular fertilizers are the cheapest and most readily available. If everything isn’t mixed exactly right, there can be some residue at the bottom of the tank. As a practical matter, however, it’s a relatively minor issue.

Some hydroseeding professionals never put fertilizer in their tanks at all, preferring to spread it separately. That’s because the high salt and ammonia content of chemical fertilizer corrodes metal tanks. On the other hand, there are tanks, especially on jet-agitation machines, that are usually plastic, while mechanically-agitated models almost always have metal ones.

However, proper maintenance practices can extend the life of your equipment.

Organic fertilizer alternatives

Homeowners, commercial and government clients are increasingly desirous of “going green.”

They’re concerned about runoff, and can’t risk having NPK from chemical fertilizers getting into nearby bodies of water.

Is there a growing market for this? “Only when I get involved,” jokes Greg Savisky, owner of Savisky Pro Turf, Butler, Pennsylvania. In his opinion, there would be much more organic hydroseeding going on, if not for one factor in particular.

That factor is cost. Organic fertilizer costs anywhere from 20 to 25 percent more than chemical fertilizers. When Holmgren heard about some of the work Savisky had been doing, he asked for his help with an organic job on a sandy site. With some sleuthing, Savisky has been able to find some cheaper sources for organic soil enhancements. “I worked out a decent formula, and it wasn’t nearly as expensive as Holmgren thought it would be.” Now, Holmgren partners with Savisky on all his organic-spec jobs.

So, let’s cut to the chase. If the organic approach is so much better, why isn’t everyone using it? Is it just because of cost? “A lot of people don’t know about this approach,” said Savisky, “but there are more and more continuing education classes available now, so more people are starting to find out.”

Other additives and applications

There are some other things that can supplement your slurry. Copolymers, which can hold 400 times their weight in water and slowly release it to new seedlings, can be added when water is scarce. Microbes and biostimulants to jump-start growth can also be thrown into the tank.

Hydroseeding components aren’t the only things that can go in your tank. Hydroseeders are also used to apply ‘alternative daily covers,’ like sprayed-on BFM blankets over piles of fly ash (the residue from coal-burning electric plants) and landfills. A BFM blanket can keep out the birds and keep in the odor and, unlike dirt, new garbage can be piled right on top of a sprayed cover. Spraying covers can be a good source of off-season revenue for you.

So, what’s in your tank?

Also in Featured Articles

In many ways, we are fortunate that, in our chosen profession, we are able to help people when certain disasters occur: the tornadoes in Missouri, Oklahoma, Louisiana and Georgia, the flooding in Louisiana, the snows in the northeastern part of the country, the rain in California, and the snow in Colorado....

Do not miss another issue.
Read the new issue of Soil Erosion Magazine online