String Trimmers Explained: Choosing and Using One Well

A mower leaves a ragged fringe wherever it cannot reach: along fences, around trees, beside walls and at the edge of paths. A string trimmer, sometimes called a strimmer or brush cutter in its heavier forms, solves that problem with a spinning line that cuts grass and light weeds. Used well, it gives a crisp edge and a tidy finish. Used carelessly, it scalps the lawn, damages bark and throws stones. Choosing the right type and learning a steady technique makes the difference.

Start with the job. Edging a small lawn and trimming around a few trees is light work, suited to a small battery or corded trimmer. Clearing long grass along a fence line, cutting around a large garden, or tackling thick weeds needs a more powerful battery or petrol model, and possibly a brush blade rather than line alone. A trimmer that is too light for thick work will stall, wear line quickly and frustrate you, while a heavy petrol brush cutter is overkill for a small, tidy lawn and tiring to hold for a short edging job.

Shaft, head and line

Shaft shape affects comfort and reach. A straight shaft reaches further under bushes and over a bank, and suits taller users and larger gardens, but it is heavier and can feel less balanced. A curved shaft is lighter, more compact and easier to handle for edging and small areas, but it reaches less far and gives less leverage on thick growth. Some models split in two for storage and transport, which helps if space is tight, though the joint adds a little weight and a point that needs occasional checking for looseness.

The cutting head holds the line, and there are several types. A bump-feed head releases more line when you tap it on the ground, which is convenient and common on domestic trimmers. An automatic-feed head releases line as needed, but can waste line if it feeds too often. A fixed-line head, where you thread short lengths of line by hand, is simple and robust, and suits heavier work. Whichever type you have, learn how to reload it before you need to do it in the middle of a job, and keep a spare spool or length of line in the shed.

Line diameter matters. Thinner line, around 1.6 to 2.0 millimetres, suits light grass and edging, cuts cleanly and uses less power. Thicker line, around 2.4 to 2.7 millimetres, lasts longer and cuts thicker weeds, but needs more power and can be harsher on lawn edges. Very thick line or a brush blade is for heavy clearing, not for a domestic lawn edge. Using line that is too thick for a small trimmer strains the motor and shortens runtime, while line that is too thin for thick weeds breaks constantly. Match line to the trimmer's specification in the manual, and do not improvise with wire or other materials, which are dangerous and can damage the tool.

Battery, petrol and corded options

Battery trimmers suit most domestic gardens. They are quiet, light, start instantly and need little maintenance beyond cleaning and line replacement. Runtime depends on battery size and grass thickness, and a common guideline is that a medium battery may give 30 to 60 minutes of light trimming, less in thick grass. If your garden needs longer, a second battery or a larger battery solves the problem more pleasantly than a petrol model for many users. For a broader comparison of power systems, see Battery vs Petrol Garden Tools: An Honest Comparison.

Petrol trimmers offer longer uninterrupted runtime and more power for thick, tall growth and large areas, at the cost of noise, vibration, exhaust and engine maintenance. They suit a large garden, a rural plot or a job far from charging. Corded electric trimmers are low cost and light, and suit a small garden near a power point, but the cable limits reach and must be kept clear of the cutting head. Whatever power source you choose, check weight and balance in use: a trimmer held at arm's length for half an hour should feel manageable, not a strain on shoulders and wrists.

For edging, some trimmers rotate the head to a vertical position, which gives a clean line along a path or driveway. If neat edges matter to you, check that feature and practise on a straight path first. A trimmer used as an edger can also be used to tidy the lawn edge after mowing; How to Mow a Lawn Properly: Height, Pattern and Timing explains how mowing height and pattern affect the finish you are edging.

Technique: edging, trimming and safety

Good technique is steady and unhurried. Hold the trimmer with both hands, keep the head low and level, and let the line do the cutting rather than forcing it into the grass. Move in a slow, sweeping arc, cutting a little at a time, and step back to check your line rather than trying to finish in one fast pass. For edging along a path, hold the head vertical and walk slowly, keeping the line just at the edge, not digging into soil or path. For trimming around a tree, keep the line clear of bark, because even light contact can wound bark and harm the tree over time.

Avoid scalping, which happens when the head is held too low or tilted, cutting grass down to bare soil. Scalped patches look pale, dry out quickly and invite weeds. It is better to leave grass slightly longer and trim again in a few days than to cut too low in one pass. Avoid trimming wet grass if you can, because it clumps, cuts unevenly and throws more debris. Work away from beds you have just planted, and keep the line away from irrigation tubing, hose pipes and low cables, which can be cut easily.

Safety is essential with a trimmer, because the line throws stones, soil and cuttings at speed. Wear eye protection, sturdy closed footwear, long trousers and gloves, and keep children, pets and bystanders well clear, at least 15 metres away as a common guideline. Check the area before you start for stones, wire, toys and other objects that could be thrown. Do not use a trimmer overhead or on a ladder, and for thick brush, slopes or work near roads, consider whether a professional or a different tool would be safer. After use, clean grass from the head and vents, check the line, and store the trimmer dry with the battery removed or the petrol tank handled according to the manual.

Common mistakes

• Holding the head too low or tilted, scalping the lawn instead of trimming it evenly.
• Using line that is too thick for a small trimmer, or too thin for thick weeds, so it breaks or strains the motor.
• Trimming against tree bark, which wounds the tree, instead of keeping a clear gap around the trunk.
• Working too fast in one pass, leaving an uneven edge, instead of sweeping slowly and checking the line.
• Forgetting eye protection and clearing the area of stones and debris before starting.
• Letting line run too long or too short, which reduces cutting efficiency and can unbalance the head.
• Storing a trimmer dirty and wet, so vents clog and the head seizes before the next use.

A string trimmer earns its place when it is matched to the job, fitted with the right line, and used with a slow, level technique. Start with a light model for a small garden, step up in power only if your grass and area demand it, and practise edging on a straight path before tackling a curved border. With eye protection, a clear area and a steady hand, you will get the crisp finish a mower alone cannot give, without damaging lawn, bark or beds.