Choosing a lawn mower: rotary, cylinder, cordless and robot compared

Saturday morning on an ordinary residential street. A petrol mower roars away on the left, a robot has been humming across a lawn since breakfast round the back, and opposite someone is pushing a hand cylinder mower you only notice once it reaches the fence. Three machines, three convictions, one and the same job.

Two days later you can see the difference. One lawn lies under a pale grey haze, one is evenly dense, and on the third there are blades the mower laid flat instead of cutting. That has little to do with the purchase price and a lot to do with which technology suits which lawn.

One thing at a time: what happens under the hood, which drive belongs on which area, what responsibility a robot mower brings with it, and when you are actually allowed to mow.

Rotary mowers: the standard, and why they leave grey tips

The price you pay is the cut surface: not a clean edge but a torn one. With a sharp blade the wound stays small and closes quickly. With a blunt blade the mower frays the tips, they dry out from the top down, and two days later the lawn lies under a grey haze. Large wounds are also a comfortable way in for fungal disease.

Even so, it deserves its place as the standard machine. It handles a family lawn that has stood a week too long, and the cutting height usually adjusts from 2 to 8 cm. As a mulching version it has a closed deck and a special blade: the clippings circle under the hood until they are fine enough, then drop back into the sward. That only works with short, dry grass.

How often you need to sharpen depends on the soil: on sandy, stony ground the edge goes blunt far faster. As a rule of thumb, reckon on 20 to 25 operating hours, so once or twice a season in a domestic garden. If you sharpened in spring, now, in late July · CW 31, is the moment to take on the second round, before the lawn picks up again in late summer. How to set the edge is covered in sharpening and caring for garden tools.

Cylinder mowers: the cleanest cut, under the tightest conditions

You only get that cut under tight conditions. The lawn has to be level, because the reel does not follow a dip, and any larger stone will bend a blade. The grass has to be short, usually 2 to 4 cm, and it has to be dry. Long or damp growth simply folds over in front of the reel and gets driven over instead of cut.

The weeds are a factor too. Daisies, white clover and dandelions press themselves flat against the ground, and the reel barely picks them up. If you want to change what grows there, the routes are in clover and dandelions in the lawn without chemicals.

The hand pushed cylinder mower is underrated all the same: no power, no fuel, no cable, just the whirr of the reel. It weighs little, has hardly any wearing parts, and still works after fifteen years in the shed. Realistically you will push it over up to about 200 m², and you have to go out twice a week. The striped look people associate with an English ornamental lawn, by the way, does not come from the cut at all but from a rear roller: it presses the grass over in the direction of travel, and the light catches each strip differently. Mainly powered cylinder mowers have that roller; most simple hand mowers run on wheels at the sides and leave no stripes.

Drive: mains, battery or petrol

The cutting technology decides the finish, the drive decides your everyday life.

The number that matters most on a cordless mower is rarely printed large on the box. What you can compare is watt hours, which is volts times amp hours. A 36 volt battery with 4 amp hours holds 144 watt hours, and two 18 volt batteries with 4 amp hours each add up to exactly the same. Voltage on its own tells you nothing about runtime.

1. Measure the lawn roughly

   Pacing it out is enough, a normal stride is about 75 cm. Subtract beds, paths and the patio, you are not mowing those.

2. Halve the catalogue figure

   The area per charge in the data sheet assumes short, dry grass on level ground. In long, dense growth it drops sharply, often to half. Plan with half and you will not be disappointed. Wet grass is another matter: most manuals for mains and cordless mowers rule it out altogether.

3. Weigh charging time against mowing time

   On many machines the battery takes longer to charge than it lasts. If your lawn runs just past one charge, a second battery is not a luxury.

Robot mowers: the machine that carries the most responsibility

The robot works differently from everything above. It runs almost daily and takes only a few millimetres each time, cutting with small razor like blades on a rotating disc. The clippings are so short that they fall between the blades of grass and rot down there. That suits the sward: the lawn is never put under the stress of a hard cut back, it stays dense and fine leaved, and part of the nitrogen stays in the cycle, so you get by with less fertiliser.

Navigation is where the systems part company. A boundary wire is laid once around the edge of the lawn and sends a signal the robot turns at: unglamorous, robust, and it works under trees too. Laying it is genuine work, and a broken wire after scarifying is the classic fault. Systems with GPS and RTK correction need no wire, drive in lanes rather than a random pattern, and can be split into zones in an app. They need a clear view of the sky; under dense canopies, in narrow courtyards and against tall house walls the accuracy collapses.

Two limits apply to every model: the edges along walls and bed borders stay a hand job, and climbing ability sits somewhere around 25 to 45 per cent depending on the machine, which rules a robot out on a proper slope.

Daytime running has a flip side, though. While small children or pets are on the lawn, the robot should be paused. The blades are razor sharp, and the lift and tilt sensors do not reliably detect a child's foot lying in the way. Block out playtime in the app schedule and the two never meet.

That leaves the small stuff. The blades are cheap consumables, so change them every four to eight weeks, otherwise your robot starts tearing the grass too. And if you have crocuses naturalised in the lawn, keep the robot out of that zone in spring until the foliage has died back. Otherwise the flowers are gone within two years.

Which machine suits which lawn

On a slope, what counts is the figure in your manual, usually up to about 20 degrees for a pedestrian mower and considerably less for a ride on. Behind a hand mower you always work across the slope; on a ride on you drive straight up and down instead, never across. Otherwise the hand mower slides back towards you and the ride on tips sideways. Above roughly 25 degrees a lawn mower is the wrong machine altogether, and you work with a brush cutter or a sickle bar mower.

Which cutting height is right depends on the lawn, not on the price of the machine. For a family lawn 4 to 5 cm is a good standard, and in a heatwave rather 6 to 8 cm, because longer blades shade the soil. An ornamental lawn runs at 2 to 3 cm, which is where the cylinder mower is at home; above 4 cm it cannot keep up, so in the summer heat the rotary mower takes over. And the one third rule always applies: never take off more than a third of the blade length at once. Everything else is in mowing your lawn properly.

Noise and the law: when you are allowed to mow

In Germany this is governed by the 32nd ordinance to the Federal Immission Control Act, the equipment and machinery noise protection ordinance. It applies in pure, general and special residential areas, in small settlement areas, in special areas serving recreation, in spa and clinic areas and in areas for holiday accommodation, and on the grounds of hospitals and care homes. The basic rule for every machine in the annex: banned all day on Sundays and public holidays, and banned on weekdays from 8pm to 7am. The lawn mower sits in that annex under number 32. In mixed, village and commercial areas and in open country the ordinance does not apply; there the public holiday acts of the individual states and local by laws set the quiet hours.

The extra quiet periods people know about, weekdays from 7 to 9, 1 to 3 and 5 to 8, do not apply to lawn mowers. They cover brush cutters, strimmers, leaf blowers and leaf collectors, and even there only if the machine carries no EU Ecolabel. So under federal law you may mow at 1pm, while tidying the edges afterwards with a strimmer can be forbidden.

The more important sentence sits in section 7 paragraph 3: further reaching state law protecting noise sensitive uses remains untouched. It is through state law that local by laws come into play. Plenty of council by laws set a midday quiet period, often 1 to 3pm. Building rules can be tighter too, and on an allotment site the site regulations are usually the stricter rule. In Austria the states and municipalities decide; night time quiet from 10pm, a Sunday and public holiday ban and, in many places, a midday break are typical. In Switzerland the times sit in cantonal and municipal police regulations.

Nothing different applies to a robot mower. Number 32 of the annex simply says lawn mower and excludes only agricultural and forestry machinery and multi purpose machines above 20 kW; there is nothing in there about being hand guided. And a robot mower carries its own guaranteed sound power level under the EU outdoor noise directive, so it is a lawn mower within the meaning of that list. In the areas named above the Sunday and public holiday ban and the 8pm to 7am quiet period therefore apply to it as well. Quite apart from that, running at night is ruled out by the hedgehogs anyway. A window of 10am to 5pm settles the night time quiet and the hedgehogs with one setting. Sundays, public holidays and any local midday quiet period you have to block out in the schedule on top of that.

Maintenance: what each machine needs over the year

1. Sharpen and balance the blade

   Take the battery out; on a petrol mower run the tank as empty as you can and pull the spark plug cap. Then tip it so the spark plug stays uppermost and the air filter does not point downwards, and never beyond 90 degrees: otherwise oil runs into the cylinder and exhaust and petrol leaks from the filler cap. Only handle the blade with cut resistant gloves. Nicks and a raised burr mean it needs regrinding, at a shallow angle and taking the same amount off both sides. Then hang the blade on a nail through its centre hole; if one side drops, take a little more material off there. When you bolt it back on, use the torque from the manual. An unbalanced blade will chew through the engine bearing.

2. Scrape the deck

   Damp grass dries into a solid layer under the hood and throttles the airflow. Without airflow no blade of grass stands up and the box stops filling. A wooden scraper is enough.

3. Overwinter the battery

   Lithium ion batteries like being neither completely full nor completely empty. Store yours at roughly 40 to 60 per cent charge, frost free at 10 to 20 degrees, so indoors rather than in the shed.

4. Get the petrol mower through winter

   Change the oil, clean the air filter, check the spark plug. Fuel with an ethanol content ages and leaves deposits in the carburettor after a few months: run the tank dry or add a stabiliser.

There is no single right lawn mower, only the one that suits your lawn and your patience. Note in your garden journal when you sharpened the blade and when you changed the robot blades, and set the sharpening up as a recurring task. After two or three years your own entries will show you which weeks you really mow, when the lawn pauses in the summer heat, and how quickly your soil takes the edge off. That is more accurate than any rule of thumb from a magazine.

Common questions about lawn mowers

Which is better, a rotary mower or a cylinder mower?

It depends on the lawn. A cylinder mower shears the grass cleanly between the reel and the bottom blade and gives the better finish, but it needs a level, stone free lawn, short grass of 2 to 4 cm and dry conditions. A rotary mower knocks the grass off with a spinning blade, so the finish is coarser, but it copes with long grass, bumps and fallen leaves. For a family lawn the rotary mower is right, for a short ornamental lawn the cylinder mower.

How big can a lawn be for a cordless mower?

Up to around 800 m² a cordless mower is the most sensible machine. What matters is not the voltage but the energy in watt hours, which is volts times amp hours. Reckon on half the stated area per charge, because those figures assume short, dry grass. If your lawn runs just past one charge, budget for a second battery.

When am I allowed to mow the lawn on a Sunday?

In residential areas, not at all. The German 32nd BImSchV bans running a lawn mower there all day on Sundays and public holidays, with a further ban on weekdays from 8pm to 7am. That includes robot mowers. In mixed, village and commercial areas the ordinance does not apply, and the public holiday acts of the states govern Sundays instead. Local by laws and allotment rules may be stricter and often set a midday quiet period. In Austria and Switzerland states, cantons and municipalities decide, and Sunday is off limits almost everywhere there too.

Are robot mowers dangerous for hedgehogs?

Yes, if they run at night or at dusk. Hedgehogs are nocturnal and do not flee from danger, they curl up and stay put. The sensors do not reliably detect a curled up hedgehog and the injuries are often fatal. Set mowing to bright daylight, roughly 10am to 5pm. Hedgehogs are strictly protected in Germany, and in Austria and Switzerland as well.

How often do I need to sharpen the mower blade?

As a rule of thumb, reckon on 20 to 25 operating hours, so once or twice a season in a domestic garden. On sandy or stony soil the edge goes blunt faster. The best clue comes from the lawn itself: if a pale grey haze lies over the green two days after mowing, the tips are frayed. After sharpening, always rebalance.

Does a robot mower need a boundary wire?

Not necessarily any more. Models with GPS and RTK correction, or with camera navigation, manage without a wire, drive in systematic lanes and can be split into zones in an app. They need a clear view of the sky; under dense tree canopies and in narrow courtyards the positioning goes vague. A boundary wire is less fussy and cheaper, but it costs you the work of laying it.