For grass to become lawn, it must be transformed into a uniform mat of low-growing turf.
Left unchallenged by a mower´s blade, common lawn species such as blue couch will grow up to 20 cm high and green couch to 40 cm. As author Michael Pollan so eloquently put it, lawns are ´nature under culture´s boot´.
Mowing develops a smooth lawn surface by controlling the taller growth of grasses and weeds.
Types of mowers
The most common mower used for Australian home lawns is a rotary mower. It should have free-moving wheels with an easy-to-use height adjustment. The blades should be mounted just slightly higher than the bottom of the surrounding base. Blades mounted higher than this will result in the base being dragged through the lawn during mowing.
A variant of the rotary mower is the hover mower, which does not have wheels and floats on a cushion of air.
In less common use is the reel mower, which produces a fine finish for the more discerning homeowner. It is unsuited to long grass, stony areas and uneven ground.
What height should I cut my lawn?
As a process, mowing is essentially detrimental to the plant. By removing leaves and shoots, mowing affects the above-ground growth and the health of the root system. Roots rely on the top growth for the carbohydrates needed to sustain their development. Generally, the closer the mowing height, the more vulnerable and shallow the root system.
Fortunately our main turf species have evolved under grazing pressure and generally cope well with regular mowing. However, if the root system is under stress for any reason (e.g. too dry, too wet, too hot, too cold, or damaged by disease, insects or recent herbicide treatment), the safest option for lawn health is to raise the height of cut and to mow more frequently to compensate.
The best cut height varies with the turf species, or even cultivar, grown. Leaving the grass longer helps retain soil moisture and reduces susceptibility to disease. However, as the grass density tends to thin when allowed to grow taller, this can also favour weeds establishing.
Under shorter cutting heights, the grass will thicken and choke some weeds, but this could also lead to increased thatch build-up in some grasses.
Shorter mowing heights give a more manicured look to the lawn, but can also lead to some scalping if not mown frequently. Provided the turf is not water stressed, lower mowing heights can be used during the warmer months when the growth rate is higher.
|Species||Mowing height (mm)|
|Green couch (Cynodon dactylon)||15-30|
|Buffalo grass (Stenotaphrum secundatum)||30-50|
|Kikuyu (Pennisetum clandestinum)||30-50|
|Japanese lawn grass (Zoysia japonica)||15-30|
|Manila grass (Zoysia matrella)||10-20|
|Seashore paspalum (Paspalum vaginatum)||15-30|
|Sweet smother (Dactyloctenium australe)||30-50|
|Queensland blue couch (Digitaria didactyla)||15-30|
|Broadleaf carpet grass (Axonopus compressus)||30-50|
Warm season turf grows most actively above 25°C, while growth ceases below about 10°C at night. Other factors such as the species and cultivar used, the age of the lawn, evaporation rates, rainfall and watering, the soil’s physical and chemical status, fertiliser application, weeds, insects and disease can all affect how often your lawn needs mowing.
As a rough guide, green couch should be mowed weekly in summer and fortnightly in winter, while blue couch can be mown every 7-14 days in spring and summer and every 21-28 days in autumn and winter. The coarser, more popular buffalo grass cultivars grow vigorously in summer, particularly when fertilised. They require more frequent mowing than the couches to minimise scalping and maintain good turf quality – typically up to two times a week under good growing conditions, but during winter, buffalo grass can be left for at least 1-2 weeks between mowings.
Scalping can occur where the turf is mowed below the minimum height recommended, or where mowing removes more than one-third of the unmown sward height. In the process, the unsightly thatch layer or even bare soil becomes exposed. Even in the tropics, lawns can take a long time to recover from such damage, providing an opportunity for weeds to take hold in scalped areas. To avoid scalping:
- Level out bumps and dips in the lawn. These are common after trenches have settled after in-filling. Spreading quality topsoil evenly to level will take care of this problem.
- Check that the mower frame is rigid and not dropping at the front.
- Mow with uniform pressure. Do not force the front of the mower into the lawn.
- Mow at the recommended mowing height for the species you are growing.
- For overgrown lawns, never remove more than one-third of the unmown height in a single cut. If a tall lawn needs to be reduced in height, this should be done in stages until the preferred height is reached.
- Mow only when the soil is dry enough to fully support the weight of the mower, without the wheels sinking into mud.
Catching or mulching?
The decision to catch or to mulch grass clippings is an individual one. For lawns with a thatch or disease problem, it is desirable to catch and remove clippings. However, for an establishing or droughted lawn, mulching will help retain soil moisture, return nutrients to the soil and build up soil organic matter. Because there is no catcher to be emptied, mulch mowing speeds up the operation. Wet grass will quickly increase the weight of the catcher, but it also cannot be spread evenly back onto the surface with mulch mowing.
Catching the clippings has the advantage of providing finely divided raw material for composting or for mulch over garden beds and around trees. However, it can also create a disposal problem. Mulching, particularly when damp or wet, can leave grass residues on the surface of the lawn, which can then be picked up on shoes and wheels and deposited onto paving and flooring.
Whether you catch or mulch, mowing dry grass will always be easier and more effective than mowing wet grass.
Irrespective of the choice of mower, it is important to keep the blades sharp. Dull blades cause ´feathering´ of the cut leaf (i.e. ragged and damaged cut leaf edges) and produce an uneven look to the lawn surface. The torn leaf edges will lose a lot of water, allowing diseases to enter into the plant.
Pick up sticks, stones and debris before mowing to prevent injuries and mower damage from projectiles.