Much about Mulch

Many C&D recyclers have turned to mulch production as an end market for their wood scrap. While a handful of states allow C&D wood to be turned into mulch, processors of C&D material in those states find that entering the mulch business can be a profitable venture. Manufacturers of horizontal grinders design their equipment to meet the many needs of various mulch producers.

A number of variables are involved in operating a successful mulch producing operation. According to Michael Stanton, Northeast U.S. assistant regional manager of Winn, Mich.-based Morbark, the three most important factors in mulch production are having the resources to obtain raw material at a reasonable price, being able to manufacture and color the mulch efficiently and cost effectively and having a consistent distribution network established, whether it is for the wholesale or retail market.

Wood for mulch production has been particularly scarce on the East Coast because paper mills traditionally provided much of the wood used to make mulch. Because of mill shutdowns and the use of wood in paper mill boilers, mulch producers are facing tough competition to secure feedstock. This makes utilizing C&D wood an even more appealing option in states where it is allowed. The key is that the wood must be free from contaminants.

Tim Griffing, assistant engineer of design/stationary facilities at Newton, N.H.-based CBI, says that if a state allows C&D wood to be used to produce mulch, it can be more profitable than selling the wood scrap to a boiler plant. “If it is allowed, it is a great way to go,” he says.
Equipment manufacturers share the following considerations that can help mulch producers get the best quality product and find a reliable market for it.

1. Use clean feedstock. Several staes allow what the industry refers to as type A wood or untreated C&D wood to be used for mulch production. Pallets are another source of wood for mulch producers that Griffing says work well with coloring agents.

Stanton says that the cleaner the raw material, the better for colored mulch production, generally. “Used and broken pallets are a common feedstock in the colored mulch market, as they are readily available and, at the same time, absorb and retain colorant well,” he says “Stumps and other land-clearing debris can take more processing and colorant to make a high quality end product, but are commonly used and can be made into a quality product, especially when producing a darker (brown or black) color mulch.”

He adds that hardwood bark scrap from sawmills is a common feedstock in certain parts of the country, as it is accessible, makes a nice finished product and doesn’t require colorant when properly processed.

As for C&D recyclers trying to make and sell mulch, the primary obstacle is sorting contaminants such as rock, brick and metal from incoming raw material prior to grinding the wood, according to Stanton. He adds that two-by-fours are similar to pallet wood, as they are very clean and can be dry, so they accept colorant well. Plywood is not ideal, though, as it doesn’t shred like other wood does and instead breaks up into inconsistent pieces, he adds.

According to Charlie Bagnall of Eugene, Ore.-based Peterson, bark is the best material for mulch. “It performs its task of curtailing weeds in flowerbeds,” he says. “It breaks down to be a beneficial nutrient for the soil.”

Bagnall recommends virgin material over using C&D wood because of the risk of contaminants; but, a clean, hand-sorted wood from a C&D material stream can be an alternative.
“It has to be a clean, sorted wood, emphasizes Griffing. The wood may need to be tested for quality, he says, adding, “There is really no reason why it shouldn’t be used.”

2. Limit moisture and fines. Equipment manufacturers agree that limiting moisture in feedstock is important. Colorant tends to be absorbed better when less moisture is present. Colorant is a major expense, so the less used, the better. Less moisture also means the finished mulch will weigh less and, therefore, cost less to transport.

In addition to high moisture content increasing the amount of colorant used, fines also can create a scenario in which more colorant is required. “If a mulch producer can eliminate or minimize the amount of fines in the feedstock, the less colorant it will take to make a quality end product,” says Griffing. “Fines soak up colorant, which increases your cost per yard to produce [mulch].”

He adds that many high-volume colored mulch producers screen feedstock prior to coloring to eliminate fines.
Liquid colorants work best when applied at 1.5 to 2 pounds per yard. Water is necessary in processing to the point that it isn’t running out from under the machine, because it helps the wood to absorb the colorant better than extremely dry wood might. For operations processing less than 10,000 yards per year of mulch, it is beneficial to apply colorant with the grinding machine, according to advocates of this technique. For operations that produce more mulch, a standalone coloring system may be necessary.

The first thing mulch producers need to determine is the most popular mulch colors. Next, they need to determine how many pounds of colorant per cubic yard will be needed, says Bagnall. The amount could vary from 1 to 3 pounds of colorant per cubic yard.

“Quite quickly, mulch producers who use liquid dye find out that a grinder with a lower rotor rpm produces less sawdust and, thus, uses far less dye than a higher speed rotor,” he says.
Liquid dye is preferred in states such as Pennsylvania, Ohio, New Jersey, Southern New York and further south, according to Bagnall. “North of there, powder dying is the preferred style due to colder temperatures that will freeze the liquids,” he says.

3. Determine equipment needs. Stanton says the key to properly sizing a grinder for each operation is determining the typical size of the feedstock being processed and the required volume of end product. The Morbark model 1600 tub grinder and model 6600 wood hog are often used for high-volume mulch production, he says.
Generally a 1.5-inch to 3-inch screen is used when making a high quality mulch product. Screen size will vary with the species of wood and the desired size of end product, sources say.
Griffing says screen combinations and sizes differ, depending on the variety of mulch being produced. “Screen combinations and sizes differ with every customer out there,” he says. Some use screens of the same size, while others have a progressive screen setup.

Finer and coarser mulches are used in different applications. “Everyone has their own recipe, their own thought on what is best,” he says.

The Northeast tends to produce a small mulch. The South produces a bigger, bulkier mulch. Everyone has a different sizing preference, from a double grind for fine mulch to a single grind for coarse mulch, explains Griffing.

CBI supplies vertical-feed, horizontal-feed, medium-speed and high-speed grinders all for mulch producers.

Upturn, horizontal grinders have become the preferred style for use in producing mulch, according to Bagnall. “The reason is that this style of grinder produces high volumes of material; but, because of the lower rotor speed it generates very little fines or sawdust.” He adds, “This style of grinder typically has a longer wear life on wear parts over older styles of grinders, thus lowering operating costs.”

To optimize mulch, production and cost, Peterson’s Michael Spreadbury recommends varying the opening sizes from the first to last grate. “The openings closest to the anvil should be the smallest to minimize spears. The screen openings can then be progressively larger away from the anvil to increase production,” says Spreadbury.

4. Stockpile with care. Most colored mulch producers try to avoid stockpiling their finished products for long periods, according to Stanton. Colorant can fade over time and wood can decompose, he explains. Both effects decrease the overall value of the end product, he warns.

Peterson’s Derek Izworski suggests storing dyed mulch under roof to avoid exposure to rain and sun, which can cause discoloration. “Stacking conveyors work best, as running the equipment over the pile causes compaction,” making the material more susceptible to fire, he says.

Bagnall agrees that conveyor stockpiling is ideal, as it is more cost effective than pushing the product into piles with a dozer.
“Colored mulch can lose its color vibrancy if left outside in the elements for too long and be less saleable,” he says. He adds that “green” wood that has been coarsely ground needs to be segregated from the main piles because of its higher oxygen levels, which can result in a mulch fire. The finer the product is ground up, the less combustible it becomes, he adds.

5. Understand the market. Factors to consider when deciding whether to enter the mulch business include understanding the size of the local market and existing competitors. If the region has watering restrictions or high water costs, more lawns will be converted to grassless landscapes, which will increase the demand for mulch.

The key consideration, however, in a business plan for mulch production is the long-term availability and cost of feedstock, according to Spreadbury. Pulpwood and biomass energy generators will compete for raw materials in some geographic areas, he adds.

In addition, most mulch yards require a state recycling permit. Obtaining the required permits can be challenging. “This will be the most arduous part of the startup,” Spreadbury says. “Once that’s done, you’ll need to secure feedstock for the mulch.”

In urban areas, he says, feedstock supplies will be heavily reliant on tree service companies and on pallet recycling. Outside of the urban areas, land-clearing and logging debris will be more plentiful.

Understanding the market also means knowing what types of mulch sell in a specific region and who a mulch producer plans to sell the product to.

While producing mulch can be a more profitable end market than wood fuel, it is important to be informed on what techniques work.