Do I really need a string trimmer if I have a robot mower?

Almost certainly, yes. A robot mower's cutting disc sits inboard from its chassis edge, so it lifts or stops short of walls, fences and flower beds rather than risk a collision — leaving a narrow uncut strip along every boundary. This site has already covered the OEM hardware trying to solve that (Segway's EdgeMaestro arm, Anthbot's EdgeEase, Mammotion's edge-cutting accessory), but as of this review none of those three has actually shipped. A standard cordless string trimmer is the only way to finish those edges today, on any current-generation robot mower.

What's the best string trimmer to pair with a robot mower?

For most yards, the RYOBI RY40250 is the best fit: $149 at ryobitools.com, a 40V battery, 15-inch swath, and compatibility with RYOBI's Expand-It attachment system, so the same battery can also run an edger or blower head. If you want to spend a few minutes a month instead of every week, EGO's ST1623T ($329.99) uses auto-sensing LINE IQ line feed so you never bump-feed it, and its 56V motor and 16-inch swath make quick work of a full perimeter. On a tight budget or for a small lot, the Worx WG163 ($84.99) is 5.29 lbs with a built-in edger wheel and runs on Worx's 20V PowerShare batteries.

Can I use the same battery platform as my robot mower's trimmer attachment?

Not yet, in almost every case. Robot mowers from Segway, Mammotion, Husqvarna and the rest use sealed, mower-specific battery packs that don't interchange with any handheld tool. The one practical cross-platform angle is Worx and its premium sibling Kress — both owned by Positec — but Kress's RTKⁿ mowers use their own internal packs too, so buying a Worx string trimmer doesn't save you a battery purchase even if you already own a Worx Landroid.

How often do I actually need to trim the edges my robot mower misses?

Roughly every one to two weeks during peak growing season, less often in spring and fall — the uncut strip is typically only an inch or two wide, so it grows at the same rate as the rest of your lawn but is far more visible against a crisp mowed edge. A single battery charge on any of the three trimmers below easily covers a quarter-acre's worth of perimeter in one session.

Should I just wait for a robot mower with a built-in edge-cutting arm instead?

Only if you don't mind mowing with an uncut border for a while longer. Segway's EdgeMaestro arm, Anthbot's EdgeEase trimmer arm and Mammotion's edge-cutting accessory all debuted at IFA 2026, and Anthbot's R7 is the earliest of the three with a real price attached — but even that points to a 2027 ship date. A $85–$330 string trimmer handles the exact same problem this season, on a mower you already own.

Best String Trimmer for Robot Mower Edges (2026): EGO, RYOBI & Worx Compared

Quick Answer: Every robot mower leaves an uncut strip along walls, fences and flower beds, and the OEM edge-cutting arms built to fix that — Segway’s EdgeMaestro, Anthbot’s EdgeEase, Mammotion’s accessory — all debuted at IFA 2026 and still aren’t shipping. The practical fix today is a cordless string trimmer: the RYOBI RY40250 ($149, 40V, 15-inch swath, Expand-It attachment compatible) is the best all-rounder, EGO’s ST1623T ($329.99, 56V, 16-inch, auto-feed LINE IQ) is the least work per edge, and the Worx WG163 ($84.99, 20V, 5.29 lbs) is the cheapest way to finish a small yard’s borders.

If you’ve read our robot mower edge-cutting comparison, you already know why this gap exists: a robot mower’s blade disc sits inboard from the wheels, so it backs off before touching a fence, bed edge or wall rather than risk clipping it. That review covered the three brand-new hardware attempts to close that gap with dedicated mower accessories — this one answers the question those attempts leave open for anyone shopping right now: which standalone string trimmer should you actually buy to finish the edges yourself?

The three trimmers compared

Trimmer	Battery	Swath	Line feed	Weight	Price
EGO ST1623T	56V (4.0Ah included)	16 in	Auto-sensing LINE IQ + POWERLOAD	~8 lbs	$329.99
RYOBI RY40250	40V (battery + charger included)	15 in	Bump feed, REEL-EASY head	8.92 lbs	$149
Worx WG163	20V PowerShare (2 batteries included)	12 in	Push-button CommandFeed	5.29 lbs	$84.99

1. RYOBI RY40250 — Best All-Rounder

RYOBI RY40250 (40V Expand-It)

$149 at ryobitools.com · 15-inch swath · battery + charger included

40V power with a 15-inch cutting swath — enough to clear a full perimeter edge in one pass on most residential lots, per RYOBI's own spec sheet.
Compatible with RYOBI's Expand-It attachment system, so the same 40V battery and power head can swap on an edger, pole saw or blower attachment later instead of buying a whole new tool.
Ships with the 0.080-inch dimpled line already loaded in a REEL-EASY bump-feed head — no separate line purchase needed out of the box.

Check RYOBI RY40250 price on Amazon →

Start your free Audible trial — something to listen to while you walk the edges your robot mower skipped.

The RY40250 is the pick for most people because it does one thing the other two can’t: grow with you. If you decide next season that you also want a cordless edger for a crisper line along the driveway, or a leaf blower for cleanup, RYOBI’s Expand-It and 40V ecosystem lets the same battery power all of it — a real advantage over a single-purpose trimmer at a similar price.

2. EGO ST1623T — Least Work Per Edge

EGO Power+ ST1623T (56V LINE IQ)

$329.99 · 16-inch swath · auto-sensing line feed, no bump-feeding

LINE IQ is an auto-sensing system that monitors the cutting line's length and feeds more automatically — you never stop to bump-feed or manually advance line mid-job, per EGO's own product listing.
POWERLOAD lets you feed fresh line into the head and press a button to auto-wind it, instead of hand-winding a new spool.
56V motor and a 16-inch swath — the widest and most powerful of the three — ships with a 4.0Ah battery and charger included.

Check EGO ST1623T price on Amazon →

If trimming edges every week or two feels like exactly the chore you bought a robot mower to avoid, the ST1623T is worth the premium. Auto-feed and auto-wind remove the two most annoying parts of a string trimmer — stopping to bump-feed and re-spooling line by hand — so the only manual step left is walking the perimeter.

3. Worx WG163 — Cheapest Way to Finish a Small Yard

Worx WG163 (20V PowerShare)

$84.99 · 12-inch swath · 5.29 lbs with a built-in edger wheel

At 5.29 lbs it's by far the lightest of the three — an easier tool to hold at arm's length along a long fence line than the 8-9 lb RYOBI or EGO.
Doubles as an edger: a 90° head pivot plus a built-in edger wheel lets it cut a clean vertical line along a driveway or walkway, not just trim horizontally.
Runs on Worx's 20V PowerShare platform, which also powers the brand's drills, blowers and other 20V tools if you want to build out a shared-battery toolkit.

Check Worx WG163 price on Amazon →

The WG163 won’t out-power the RYOBI or EGO on a long, overgrown edge, but for a small-to-medium lot where you’re just touching up a thin strip every couple of weeks, its light weight and built-in edger wheel make it the most pleasant tool to actually reach for.

By the numbers

$84.99 to $329.99: the price range across all three trimmers here — a 4x spread driven mostly by auto-feed convenience (EGO) versus manual bump-feed (RYOBI, Worx), per each brand’s own listings.
12 to 16 inches: the cutting swath range, meaning the EGO clears a wider path per pass than the Worx — fewer passes needed to finish the same edge.
0: OEM robot-mower edge-cutting attachments actually shipping as of this review — Segway’s EdgeMaestro, Anthbot’s EdgeEase and Mammotion’s accessory all remain unreleased since their IFA 2026 debut, per our edge-cutting comparison.

The bottom line

None of the robot-mower-specific edge-cutting hardware announced at IFA 2026 has actually reached a US cart yet, so a standalone cordless string trimmer remains the only real way to finish the strip your mower leaves behind. Buy the RYOBI RY40250 if you want room to add attachments later, the EGO ST1623T if you want the least hands-on maintenance per edge, or the Worx WG163 if you have a small lot and want the lightest, cheapest option. Already shopping for the mower itself? See our best robot lawn mower pillar, and keep an eye on our robot mower edge-cutting comparison for whenever the OEM arms finally ship. Due for a blade swap on the mower side too? Our robot lawn mower maintenance guide covers that schedule. See current string trimmer listings on Amazon →