Robot Mower Cutting Poorly? 7 Causes and Fixes

MA MowAutonomous Editorial Team · Updated 2026-06-23 · 10 min read

If your robot mower is leaving uncut strips, tearing the grass, or producing an uneven cut, the problem is usually one of seven things. This guide walks through each cause and how to fix it.

1. Dull Blades (Most Common)

Dull blades are the #1 cause of poor cutting. Dull blades tear the grass rather than cutting it cleanly, leaving frayed tips that turn brown. Fix: Replace the blades. Most mowers need new blades every 1-3 months depending on lawn size and grass type. Always keep 2-3 spare sets on hand. Replacement blades cost $15-$40 per set.

2. Mowing Wet Grass

Wet grass doesn't cut cleanly — the mower tears it rather than shearing it. Fix: Schedule mowing for mid-morning after the dew has dried, or in the afternoon. Don't mow right after rain. If your mower has a rain sensor, make sure it's enabled.

3. Grass Too Tall

If the grass has grown too tall, the mower will struggle to cut it cleanly. Fix: Manually mow the tallest areas to bring them down to 4 inches, then let the robot mower maintain from there. Going forward, increase mowing frequency.

4. Low Blade Speed

If the blade motor is running slowly, the cut quality suffers. Low blade speed is usually caused by: (1) a weak battery — charge the mower fully before mowing; (2) a clogged cutting deck — clean the underside of the deck; (3) a failing blade motor — contact the manufacturer for repair.

5. Uneven Terrain

If your lawn has bumps, dips, or ruts, the mower may scalp high spots and miss low spots. Fix: Level the lawn by topdressing low spots with topsoil and aerating compacted areas. For minor unevenness, raise the cutting height by 0.5 inches.

6. Clogged Cutting Deck

Grass buildup under the cutting deck reduces airflow and cut quality. Fix: Once a week, turn the mower over (after removing the battery) and clean the underside of the deck with a brush or plastic scraper. Don't use a metal scraper — it can damage the deck.

7. Wrong Cutting Height

If the cutting height is set too low, the mower scalps the lawn. If it's set too high, the mower doesn't cut enough. Fix: Set the cutting height based on your grass type — most cool-season grasses (Kentucky bluegrass, fescue) want 2.5-3.5 inches; most warm-season grasses (Bermuda, Zoysia) want 1.5-2.5 inches.