String Trimmer Selection and Safety - November 23, 2016
Jeff Schalau, Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County

String trimmers (also called weed eaters) are useful tools for landscape maintenance professionals and homeowners having lawns or large properties. For those considering the purchase of a string trimmer, there are multiple features to consider. Using these tools can also be hazardous to both people and landscape plants. Selecting a suitable string trimmer for your needs, keeping it in proper working order, and following a few safety guidelines will help ensure a positive experience.

Many small homeowner-sized string trimmers are powered by a120-volt electric motor. There are also battery-powered, rechargeable models. Naturally, the 120-volt models need to be connected to power via an extension cord. The advantages of the electric models are: no need for gasoline, or mixing gasoline and oil; no engine to maintain; and no struggles to get it started after itís been sitting in the shed for six months. The electric models are also quieter. Conversely, the electric units are less powerful than the larger gasoline engine models. The gasoline engine also gives you complete freedom to roam.

String trimmers generally have the engine at the upper end of a metal tube and the cutting head at the other end. A flexible cable running inside the metal tube connects the motor to the cutting head. On many smaller machines, the tube is curved near the cutting head. Heavier duty models, including most professional models, use a straight tube. Each has a flexible cable inside the tube. The straight tube models require a beveled gearbox at the head to change the angle of rotation. Straight shaft models may be more durable since the drive cable does not have to flex.

Homeowner and smaller professional string trimmers generally have a single C- or D-shaped handle for one hand and the operatorís other hand grasps the tube. Some larger professional models have a wide "bicycle-type" handle with a strap that bears the weight of the motor. The "bicycle-type" handle provides better control and is the only type of handle that should be used with a brush-cutting blade.

The standard cutting head on most units feeds out plastic string. Bump-feed heads are popular. Here, the user bumps the head on the ground to feed out more line, and the string is automatically cut to length by a blade on the safety guard. Some professional string trimmers allow the substitution of a blade for the string head. The blade may be an X-shaped steel blade for light brush or a saw blade for larger brush.

It is important to follow safety guidelines when operating string trimmers. Keep in mind that small rocks can be catapulted by the trimmer head. Serious damage to trees, shrubs and other plants often occurs where string trimmers are used. No matter how good you think you are at using a string trimmer, plants will eventually be damaged if you try to trim around the base of trees and shrubs. It is best to avoid trimming at the base of plants. These areas can be managed by spraying with glyphosate or by hand trimming.

The following are essential steps to successful string trimmer operation. Read the owner's manual carefully. Wear proper protective clothing: eye protection, trim-fitting pants and shirt, sturdy shoes, and ear protection. Be sure electric units are either double insulated or connected to a 3-prong grounded outlet. Use the type of extension cord recommended by the manufacturer. Do not use electrical powered units in damp or wet conditions. Trimmers can throw objects with force so keep children, bystanders, and pets from the working area.

Wait, thereís more. Do not operate the trimmer near windows. Keep the trimmer close but not touching the ground. Angle the unit slightly to the left to discharge trimmings away from your body. Hold the trimmer firmly with both hands in a properly balanced stance. Keep the hot engine and exhaust away from your body. Use only monofilament string recommended by the manufacturer. Never use wire or metal reinforced string as broken pieces can become lethal missiles. Never touch the string while in operation. Stop the engine and disconnect spark plug wire before servicing. Disconnect the power cord on electric units. Refuel only with engine stopped and cool. Store the unit in an area where children or untrained personnel will not have access.

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Two line trimmers showing a "straight tube" and "curved tube" design (from:

Grass Trimmer Safety
University of California Natural Resources

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Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr. #C
Prescott, AZ 86305
(928) 445-6590
Last Updated: November 16, 2016
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