Best cordless string trimmer for tall weeds and rough growth

Trimmer roundups rank on swath and runtime, which is fine if your job is a tidy lawn edge. If the job is a fence line that has not been touched since spring, the specification that decides everything is a two-digit number most listings bury: the line gauge.

The short answer

Why the line gauge is the whole story

A string trimmer cuts by whipping a plastic filament fast enough that it behaves like a blade. Against soft grass almost any filament works. Against a thick weed stem, the line either cuts through or it snaps, and thickness is what determines which.

Every break costs you: you stop, you feed line, and on a bump-feed head you do it by tapping a spinning head on the ground mid-job. Over a long session the difference between gauges is not really cutting performance, it is how many times you stop.

The picks

1. Ryobi RY402110 — the long-session tool

Heavy 0.095 in line, the widest swath here at up to 17 inches, and 67 published minutes from a 240Wh pack. Rough-growth work is slow work, so runtime matters more on this job than on any other trimmer task, and 67 minutes is more than double what the EGO kit publishes.

The adjustable head is the second reason it wins here. Narrow to 15 inches around posts and stems, widen to 17 for the open verge, all from one tool. Nothing else in our registry does that.

The cost is real and published: 12.9 lb with the 6.0Ah pack fitted, on a 72.25 inch shaft. That is the heaviest trimmer we hold specs for, held out at arm's length, and after an hour you will know it.

#ad Check the Ryobi 40V HP Whisper 17" Carbon Fiber RY402110 price on Amazon — how we're funded.

2. EGO ST1521S — 0.095 in line you never have to wind

Same heavy gauge, delivered through a POWERLOAD head that winds new line at the push of a button rather than by threading a spool. On a job where line breaks often, an automatic reload head is not a luxury feature, it is the feature.

It also carries the strongest warranty position in the category: five years on the tool, three on the battery and a published lifetime warranty on the carbon fiber shaft. Shafts are what break when a trimmer gets used as a machete, so that is a well-aimed guarantee.

The catch is the kit pack. 140Wh and 30 published minutes is a short session for rough growth, and at 4.67 watt-hours a minute it is also the thirstiest trimmer here. If this is your pick, buy it into an EGO platform where a bigger pack already exists — the logic is in bare tool or kit.

#ad Check the EGO Power+ 15" POWERLOAD Carbon Fiber ST1521S price on Amazon — how we're funded.

3. Greenworks ST80L210 — the honest skip

We include it because every roundup needs a pick you should not buy for the job on the page. The ST80L210 is genuinely good: 7.1 lb bare, the lightest published trimmer weight in our registry, a 30-minute recharge, a four-year battery warranty and a published 6200 RPM motor speed that neither EGO nor Ryobi discloses.

But 0.080 in is a lawn-edge gauge. On heavy weed stems it will break more often than the 0.095 in tools, and every break is a stop. Buy it for trimming, not for clearing.

#ad Check the Greenworks 80V 16" String Trimmer ST80L210 price on Amazon — how we're funded.

The weight problem nobody mentions

Rough-growth sessions are long, and a trimmer is the only yard tool you hold at full arm extension for the whole time. The published weights swing by 80%.

Getting more out of whichever you buy

1. Cut in stages, top down. Taking tall growth in two or three passes from the top costs less line than trying to take it at the base in one.
2. Work the tip of the line. The outer inch is doing the cutting; burying the head in the growth just loads the motor and breaks line.
3. Sweep in the direction the head spins. Debris then throws away from you rather than back over what you already cut.
4. Keep the head off the dirt. Soil and stone destroy line faster than any weed.
5. Do the fence line first, while the pack is full. Trimmers pull hardest at the start of a job, and that is exactly when you have the most energy available.

What we cannot tell you

We have not run any of these tools and no manufacturer publishes a heavy-load runtime, a line-life figure or a maximum stem diameter. Any claim about how many minutes you get in brambles would be fabricated, and this category is full of exactly that.

What is published, and what decides this page, is 0.095 in against 0.080 in, 67 minutes against 45 and 30, and 12.9 lb against 7.1. Those four numbers cover the decision.