Mowers and mower-conditioners

How it works

Modern grass mowers cut by speed rather than by scissor action. Small free-swinging knives on fast-spinning discs or drums slice through the stems as the tractor drives forward, and the cut crop is left lying in a swath behind the machine. The cutterbar rides on skids so it follows the ground, and the cutting height is set by tilting the bar or changing the skid shoes.

On a mower-conditioner the cut crop is carried straight into a conditioning unit. Rollers crimp the stems so sap can escape, while a flail or tine rotor scuffs off the waxy outer coat of grass. Either way the crop loses moisture more quickly, which means fewer days at risk of rain before baling or clamping. Swath boards at the back then spread the crop wide or gather it into a narrower row.

Main types

• Disc mower: A low, flat cutterbar carrying a row of small discs, each with two knives. It cuts fast, rarely blocks and needs little knife maintenance. Modern bars give each disc its own sealed drive, so one damaged unit can be swapped without replacing the whole bar.
• Drum mower: Two or more large drums driven from above, with knives on plates at the bottom. Fewer drive points make it simple and robust, and it works well in heavy crops, but it is heavier at the front and lays the crop in rows that usually need tedding.
• Sickle bar mower: The older reciprocating knife, working like hair clippers. It needs the least power and is cheap, but it is slow and can block in thick or laid crops.
• Mower-conditioner: A disc or sickle mower with a conditioning unit behind it. Roller conditioners suit lucerne and clover because they lose fewer leaves; flail or tine conditioners suit grass.
• Butterfly or triple mowers: A front mower plus two side-mounted rear mowers, giving very wide cutting in one pass on large silage operations.

Hooking it up to a tractor

Most rear and side mowers mount on the three-point linkage and are driven by the PTO, normally at 540 or 1,000 rpm through a gearbox. Disc mowers need at least one double-acting hydraulic service to fold the bar for transport, and mower-conditioners often need two. Large centre-pivot conditioners are trailed from the drawbar. Sickle bar mowers need the least power, disc and drum mowers need a medium-sized tractor (drum mowers also want plenty of front-end weight), and mower-conditioners need the most because the conditioner itself absorbs power.

A short history

For generations the reciprocating sickle bar was the standard mower, first behind horses and then tractors. The first mower-conditioner, sold as the Haybine, put a sickle mower and a conditioner on one machine so cutting and crimping became one job. The rotary drum mower was a European design, and disc cutterbars later replaced sickles on most farms because they run faster and block less. New Holland's disc-cutting successor to the Haybine is sold as the Discbine.

Buying and care tips

• Match the conditioner to the crop: Choose rollers for leafy legumes and flails or tines for grass. Correct adjustment matters more than the type, so learn the settings.
• Check roller gap: Rolls set too tight strip leaves and wear quickly; too loose and the crop barely crimps. Measure the gap with the PTO off and the engine stopped.
• Inspect the cutterbar: On a used mower look for leaking or noisy disc drives, worn skids and bent knife bolts. Check the gearbox oil level and colour.
• Spread the swath: A wide swath covering most of the cut area dries fastest, so set the swath boards wide unless the crop is going straight to a forager.
• Carry spare knives: Quick-change knife systems make it a minutes-long job to fit fresh blades after hitting a stone.

Questions people ask

What is the difference between a disc mower and a drum mower?

A disc mower has many small discs on a low flat bar driven from underneath, while a drum mower has a few large drums driven from above. Disc mowers cut faster and leave a wider swath; drum mowers are simpler but heavier and leave the crop in rows.

What does a conditioner do on a mower?

It crushes or scuffs the cut stems so moisture escapes more quickly. That can save a day or more of drying in the field before the crop is baled or picked up.

Should I choose a roller or a flail conditioner?

Rollers are gentler on leafy crops such as lucerne and clover. Flails or tines suit grass and need a little less power.

How much horsepower does a disc mower need?

A disc mower needs a medium-sized tractor with at least one hydraulic service; the maker's plate gives the minimum. A mower-conditioner of the same width needs noticeably more because the conditioner also takes power.

Related equipment

Sources

1. Conditioner (farming), Wikipedia
2. Selecting and maintaining hay mowing and conditioning equipment, Ohio State University Extension (ANR-0186)
3. Discbine disc mower-conditioners, New Holland Agriculture

Last checked 2026-11-01

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