Why Mower Blades Leave Uncut Stripes and How to Align the Deck

A mower that leaves uncut stripes in the grass is doing half a job. The stripes may run in lines, appear in patches, or follow the pattern of the deck. The cause is usually a simple setup issue rather than a worn machine, and fixing it restores a clean cut.

Check deck height across the width

A deck that sits tilted cuts one side lower than the other, leaving a stripe where the blade runs too high. Measure the blade tip height at each corner, and level the deck side to side and front to back. A deck that sits flat cuts evenly across its full width.

Look at blade overlap

On a multi-deck mower, the decks must overlap slightly so the cut from one deck meets the next. If the decks are spaced too far apart, a stripe remains between them. Adjust the overlap so each blade's path reaches into the next deck's cut. Side-by-side stripes usually mean this spacing.

Inspect blades for wear or bending

A blade that is blunt, bent or nicked cuts poorly and leaves a ragged strip. Check blade sharpness and condition. A bent blade also cuts at the wrong height, leaving a stripe on one side. Replace or sharpen blades, and check that they are straight and balanced.

Check the deck shell for damage

A deck dented from a hidden obstacle sits lower on one side, and the blade hits the shell or runs at the wrong height. Inspect the deck underside for dents, and check that blades clear the shell. A damaged deck is straightened or replaced rather than forced back into service.

Test on flat ground

After the adjustments, run a pass on flat, even ground and walk the cut. An even, unstriped finish means the setup is right. Note the deck height and overlap settings, so the next cut starts from a known good setup.

References

BROWN R T, DAVIES M K. Cut quality and deck alignment on rotary mowers[J]. Biosystems Engineering, 2021, 203: 320-328.

Brown, R. T., and M. K. Davies. "Cut Quality and Deck Alignment on Rotary Mowers." Biosystems Engineering, vol. 203, 2021, pp. 320-328.

Brown, R. T., & Davies, M. K. (2021). Cut quality and deck alignment on rotary mowers. Biosystems Engineering, 203, 320-328.