Garden Grinders

By Michael MacCaskey

Shredding reduces the size of your compost pile and speeds decomposition.

I used to think that a chipper-shredder didn't make sense for anyone with less than a half-acre garden. But now that so many communities have banned or restricted disposal of yard waste, and because the cost of good compost and mulch keeps rising, I gave these machines a second look.

My own compost pile was "cold compost." I heaped all the yard waste in one pile and, given enough time, it would decompose. After shredding, my compost was another story altogether. Particles were smaller and more uniform, as you'd expect. More important, a mere two days later the temperature in the center of the pile shot up to 130oF, hot enough to destroy disease organisms and some weed seeds. My cold compost pile was reduced in volume by about half. It looked neater, and it got hot!

About Chippers and Shredders

Chippers and shredders for every size and type of garden (and gardener) are available. Several electric models are available that boast light weight, quiet operation, and low cost. At the other end of the spectrum are machines with 12 or more horsepower that can chip 4- to 6-inch limbs-and sometimes whole trees-but cost several thousand dollars. But for the purposes of this article, I chose to focus only on gasoline-powered chipper-shredders in the 5 to 10 horsepower range. They are medium to heavy-duty on the homeowner scale, and are I think, most likely to meet the expectations of avid gardeners. If you anticipate processing any woody branches or fibrous materials such as corn stalks, machines in this power range are essential.

For instance, one of the machines tested for this article, an 8-horsepower shredder-chipper, in about 2 hours reduced 2- to 3-inch-diameter stems pruned from a lilac, maple, and apple, into a small pile of chips.

While the heaviest of these avid gardener chipper-shredders, at 300 pounds, is a daunting piece of equipment, it and all the others listed here are mobile on their own wheels.

Following are descriptions of the main components all chipper-shredders have in common. Some models offer options such as electric engine starting, vacuum hoses, leaf tampers, and bagging kits.

Chipping Components

Chipping Blades. Most chipper-shredders have a chipping component that is separate from the shredding mechanism. You feed branches and similar woody material through a chipping tube where it contacts the chipping blade. The hardened steel blade quickly converts the woody material into chips or mulch. The chipper-shredders we looked at have one or two of these blades, and most are 3 to 4 inches long.

Manufacturers cite the diameter of the chipping tube as the "chipping capacity," which is fair enough because tube diameter is just slightly less than blade length. But it's a bit optimistic when it comes to hard, dry, or irregularly shaped wood. Conservatively, figure a chipper can handle branches that are half as wide as the chipper blade is long.

All but two machines utilize one or two rotor-mounted chipping blades. The exceptions, both from Troy-Bilt, are designed around a commercial-chipper-style, high-rpm drum mounted with two 8-inch blades. These machines are pure chippers, with no shredding hammers or screens. They can process limbs 5 to 6 inches in diameter, and anything else from your garden or yard, though particle size is larger and more irregular.

Chipper blades need sharpening or replacement from time to time. Feeding them soil and stones dulls them fast. Check with your manufacturer. Some chipper blades are reversible, a convenient feature that reduces both downtime and costs. Before buying, consider what's involved in replacing the blade, and plan on doing so at least annually.

Shredding Components

Shredding hammers. In addition to the chipping component, chipper-shredders have a separate shredding unit that handles soft or thin material, such as leaves and compost. The hardened steel blades, called shredding hammers or flail knives, are about 3 inches long, 1 inch wide and free-swinging, like the seats on a Ferris wheel. The shredding hammers are located just below the shredder hopper, where the material is deposited into the machine.

The hammers hang when at rest but are flung outward during operation and eventually contact the material you're feeding into the machine. If a shredding hammer hits a stone or something hard, it bounces back sustaining minimal damage in the process. Some shredder units include fixed knives that are attached as rigidly as the name implies. Although they'll cut more aggressively, they also wear much faster.

In most machines, fixed knives and flail hammers are reversible. Generally, the machines with more of these blades - whether moving or fixed - the more efficient and faster the shredding.


Chipper-shredders usually include perforated metal plates or closely spaced steel bars located just beyond the shredding hammers at the discharge area of the machine. These screens or bars keep the garden waste in the shredding unit until it is small enough to pass through the holes or spaces. If you're shredding heavy, wet, or matted materials, a screen with large holes (or no screen at all) will permit most efficient shredding. If you want evenly fine-textured material, you can attach screens with 1-inch or 1/2-inch openings. Machines with screens are more likely to clog than those without screens. But those with screens are usually easy to clean out if they become jammed. On many models it's as easy as removing two or three hairpinlike fasteners. Standard screens have 1-inch openings. Smaller and larger screen openings are optional.

Check any chipper-shredder you're considering for ease of access to the shredding chamber. Jams occur no matter what kind of machine you have or how powerful it is. Easy access to the shredding chamber also makes it simpler to service the chipper knife and flail blade.

Clutch, Rotor and Engine

The Clutch. The clutch of a chipper-shredder is similar in function to a clutch found in a car or lawn tractor. It engages and disengages the rotor that holds the shredding and chipping blades. Two kinds of clutches are available: "idler lever" (or "throw") and "centrifugal."

Idler-lever clutches include a lever that you use to engage the shredding mechanism. They are relatively simple controls that give you more control over the chipping or shredding.

Centrifugal clutches engage or disengage automatically, depending on engine speed. For example, if the shredding assembly bogs down, a centrifugal clutch will automatically disengage, giving the engine time to increase power.

Machines without clutches are called "direct drive," which means that whenever the engine is operating, so is the entire shredding-chipping assembly. This means the user has less control, and these machines are harder to start because you must crank the engine and shredding-chipping mechanism at the same time. On the other hand, direct-drive machines are usually less expensive.

The Rotor

This holds the shredding hammers and chipper blade or blades. When buying a chipper-shredder, remember that rotors on clutch-equipped machines are supported by a center axle mounted on bearings at both ends. On direct-drive machines, the rotor is fitted directly onto the engine's crankshaft, which puts an extra load on the engine's main bearings. Some direct-drive chipper-shredders, add a bearing to support the end of the crankshaft, a feature that lengthens engine life significantly.


Horsepower is not the only factor determining shredder efficiency. The number of cutting knives, presence and kind of a clutch, and the size of the shredding intake throat are also important. Despite the power of the engine or the size of t hopper, if the intake throat is small you'll need either to feed debris in slowly, or use a tamper to force it down. Also, bigger engines take more muscle to start with a pull cord.

Safety Precautions

For your own safety, read and follow all the manufacturer's precautions. Most are obvious: Don't let kids play in the area while the machine is operating, don't stand and load the machine from the discharge side, always wear work gloves, and eye and ear protection; and avoid loose-fitting clothes, scarves, ties, or anything that might get caught in moving parts.

Most important is the caution, "Wear eye protection." It's always sensible, but in the case of chipper-shredders, there is a real risk. Although no stray projectiles came my way in the many hours I spent working with these machines, it can happen. Most often the debris is launched from the hopper or chipper chute, but it sometimes sneaks out around the collection bag's attachment point. Wherever it originates, it often comes fast and hard.

If the machine becomes jammed, turn it off, disconnect the spark plug, and wait for all moving parts to stop before investigating with your hands.

Another safety issue is the suction that develops, particularly on machines designed to double as vacuums. Make sure nothing except yard waste gets near this down draft. A coworker was shaking debris out of a plastic garbage sack into the shredder hopper, and the bag was sucked right out of his hands. No damage was done, but the experience was unnerving.

One necessity not always mentioned in the product manuals is a pair of loppers at your side while chipping. A few branches with forks and nubs always refuse to slide all the way down the chipper chute. You need loppers to modify these troublemakers. Of course, when not using them, keep them away from the intake openings of the machine.

Michael MacCaskey is the editorial director at the National Gardening Association.

Chipper-Shredder Manufacturers

BCS America Inc., 13601 Providence Rd., Matthews, NC 28105, (704) 846-1040

Bear Cat Co., Box 849, 237 12th St., NW, West Fargo, ND 58078, (701) 282-5520

Brave Industries Inc., 115 East Front St., Annawan, IL 61234, (309) 935-6131

Easyrake, 1001 South Ransdell Rd., Lebanon, IN 46052, (800) 777-6074

Mackissic Inc., Mighty Mac, Box 111, Parker Ford, PA 19457, (610) 495-7181

MTD Yard Machines, Box 368022, Cleveland, OH 44136, (216) 255-2600

Murray Inc., 219 Franklin Rd., Brentwood, TN 37027, (800) 251-8007

Patriot Co., 944 N. 45th St., Milwaukee, WI 53208 (414) 259-8997

Roto-Hoe Products Inc., 345 15th St., NW, Box 792, Barberton, OH 44203, (216) 753-2288

Simplicity Manufacturing Inc., and Baker Yard Waste Management Systems, 500 N. Spring St., Box 997, Port Washington, WI 53074, (414) 284-8706

Troy-Bilt/Garden Way Inc., 102nd St., 9th Ave., Troy, NY 12180, (518) 391-7000

Yard Shark, Tilton Equipment Co., Box 68, Rye, NH 03870, (800) 447-1152

Photography by Lynn Ocone

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