Step-by-step guide to mowing tall grass and light brush with a rotary cutter. PTO speed, ground speed, deck height, and safety rules for compact tractor owners.
A rotary cutter (commonly called a bush hog after the original brand) is the right tool when the grass gets too tall for a finish mower. It chops weeds, brush, saplings up to about 2 inches, and tall grass into mulch. Done wrong, it throws rocks, scalps the ground, and stalls your tractor. Done right, it clears an acre an hour without breaking a sweat.
Walk the field. Pick up rocks, scrap metal, glass bottles, and anything bigger than a golf ball. The blade tips move fast enough to throw a stone like a bullet. Mark stumps, t-posts, and irrigation valves with bright flags so you can see them from the seat.
For tall grass and brush, set the rear of the deck 4 to 6 inches off the ground and the front 1 inch lower than the rear. The forward tilt keeps the leading edge cutting cleanly and reduces the chance the cutter rides up and over thick patches. For a finish pass, lower to 3 inches with the deck level.
Engage the PTO at idle, then ramp engine RPM up to PTO speed (usually 540 RPM, marked on the tach). Pick a low gear. For thick brush, ground speed should be 1.5 to 2.5 mph. For tall grass, 3 to 4 mph. If the tractor RPM drops more than 100, you are going too fast. Ease off, let the PTO recover, and re-engage at a lower ground speed.
For very tall grass over 3 ft, mow the field twice. First pass at deck-high to knock the tops down, second pass at finish height to mulch the litter. Overlap each pass by 6 to 8 inches. Mow in a spiral from the outside in for fields, or in long parallel passes for paddocks. On any slope, drive straight up and down rather than across it: a side slope narrows the margin between the tractor's centre of gravity and its stability baseline, and that margin depends on your rear track width and how high the load sits, not on a single angle. Read the slope limits in your operator's manual.
The cutter must suit your tractor's PTO horsepower and 3-point lift. In our database the 18 rotary cutters on file need more PTO power as they get wider. The 4 foot class cutters need 15 to 18 PTO hp, the 5 foot class 20 to 25 PTO hp, the 6 foot class 25 to 30 PTO hp, and the single 84 inch cutter 50 PTO hp. Weight rises with width too, from 413 lb at the narrow end to 1,150 lb at the wide end. Run a candidate cutter through our rotary cutter compatibility check to see which models fit your tractor.
Never operate without the chain guards intact. Never let anyone near the cutter while it runs, especially children, and keep to the safe distance in your cutter's manual. Disengage the PTO and shut off the tractor before clearing a jam. Wear hearing protection, because a running cutter is loud at the seat. And lower the cutter to the ground or onto its parking stand before stepping off, never leave it in the air on the 3-point.
I've run Deere, Kubota, Massey and Kioti, mostly smaller compact and utility tractors, a few hundred hours all told: bush hogging, loader work, moving gravel, grading driveways, snow, post holes and pallet forks. This is what I've learned from that, not manufacturer data.
One setup surprised me: a 35-horse tractor with a 5-foot cutter. On paper, no problem at all. Plenty of horsepower. But get into thick, wet grass or rough ground and you find out pretty quick the spec sheet doesn't tell the whole story. Weight and traction matter just as much as horsepower sometimes.
Don't oversize your implements just because the tractor can technically handle them. If your tractor is happiest with a 5-foot cutter, just buy the 5-foot cutter. You're not saving much time with a 6-footer if you've got to crawl everywhere.
That depends on the cutter and on your tractor's PTO power, so check the cutter's PTO requirement first: the 5 foot class cutters in our database need 20 to 25 PTO hp. In very tall grass or woody brush, mow at the highest cut height first, then drop down for a second finish pass.
Start at 2 to 3 mph in tall or wet grass. Listen to the engine, if RPM drops, slow down further. Maintaining full PTO RPM (540) is more important than ground speed for a clean cut. Forcing speed in heavy material causes ragged cuts, blade damage, and tractor overheating.
Rotary cutter blades are designed to impact-cut, not slice, they don't need a razor edge. Replace blades when the cutting edge is rounded, chipped, or unbalanced. Always replace blades in pairs to keep the rotor balanced. Run a blade-balance check after replacement to avoid gearbox vibration damage.
Hearing protection, safety glasses, sturdy boots, long pants. Walk the area first to remove rocks, wire, and debris that the blades can throw. Keep bystanders at the safe distance stated in your cutter's manual, to the sides and rear. Always disengage the PTO before dismounting and never reach under the deck while the rotor is spinning.
Published 2026-04-08, last updated 2026-10-20. Figures quoted in this guide cite manufacturer documentation where available, and the tractors and attachments it references are records in the FitTractor compatibility database.