Grass trimmers can be fantastic time-savers, or terrible time wasters if you have to struggle to make them work.
We carry out independent, scientific tests designed to find out how well grass trimmers cope with challenging situations and how easy they are to use.
Keep reading to find out what our grass trimmers tests involve.
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Watch the video below to find out what we look for in a grass trimmer, and what makes the best grass trimmers quickest and easiest to use.
Grass trimmers are designed to cut areas of grass that are difficult to get at with the mower. This can be along the edge of flower borders and paths, close to a fence or under garden furniture. They're also often used to cut down long grass that has been allowed to grow for some time, such as where bulbs have been naturalised in the grass.
Many gardeners find grass trimmers useful to keep their border and path edges looking neat, so the trimmer needs to be able to cut a horizontal line.
When we cut along path and border edges, we look at:
Not all grass trimmers are designed to cut path edges. For example, large petrol brushcutters are made for cutting down meadows and weed patches, and are too powerful to carefully cut a neat line. Our tests show which models will excel at the tasks you need them for.
Some grass trimmers are designed specifically to cut down areas that are a mix of weeds and long grass, such as meadows or ground that has been left uncultivated for some time. Others struggle with this task, being too low powered to cut through tough stems and disperse the debris.
We test all our grass trimmers on long grass and rough vegetation to find out which ones can cope.
Our tests are designed to make sure you can do this task quickly and efficiently, without the line breaking repeatedly.
In our test, we pass the trimmer head close to the edge of a spade 20 times.
It's inevitable that the line will wear down and break, but some models spool out line easily and simply, while others are less user-friendly.
We also assess how easy it is to open the trimmer head and add or spool out more trimmer line.
All grass trimmers tested from 2017 onwards have been tested this way, and scores for this element of the test are not comparable with those from earlier years.
Grass trimmers vary in weight between 1.5kg and almost 6kg. But this will normally depend on the type of trimmer and the job it's designed to do.
Our expert users assess:
Vibration and noise are also important when you use a grass trimmer for a long period, so our experts assess these as well. We use a decibel meter to measure noise, and a vibration glove to see whether the grass trimmer will be uncomfortable to use.
Our experts are able to judge which grass trimmers adjust in ways that are helpful to most users. For example:
Battery life on a cordless grass trimmer is also important, so we:
Petrol grass trimmers can be devilishly hard to start, although some have modified designs to reduce the number of pulls you need and the force you need to apply. We assess how easy all our petrol grass trimmers are to start.
Lithium-ion batteries always deplete and eventually die over time, and at Which?, we believe that cordless products should last longer than the batteries they come with. That's why we no longer give cordless strimmers and trimmers Best Buys if spare batteries cannot be bought from the manufacturer – no matter how good they might be.
Some grass trimmers are designed to be great at edging the lawn, and others for making short work of meadow or bramble patches. Through our testing and assessments we discover which grass trimmers are best for specific jobs.
We categorise grass trimmers into three groups:
All the grass trimmers undergo the same tests, and we then rate them by including or excluding some of the tasks and weighting others by importance.
For example, for lawn-edging grass trimmers we don't include scores for cutting long grass and weeds, and put most of the weight on the lawn-edging task.
Similarly, when rating the heavy-duty grass trimmers we look at how well they cut long grass and weeds, and take into consideration how well they cut along a fence line and shorter grass, but ignore the marks for edging a lawn and a path.
General-purpose grass trimmers are those that score well in all tasks.
The overall score ignores price. For corded and petrol grass trimmers it is based on:
And for cordless grass trimmers it is based on:
Lawn-edging grass trimmers must score 71% or more to be a Best Buy.
General-purpose grass trimmers have to score 73% or more to be a Best Buy .
Heavy-duty grass trimmers must score 83% or more to be a Best Buy.