How do I choose the correct cutting height to mow my lawn?

Turfgrass – a mix of narrow-leaved grass species, such as Kentucky Blue and Perennial Ryegrass, commonly used for lawns – is well adapted to frequent mowing. But did you know that clipping grass too short can damage the plant and reduce how vigorously it grows?

There is a direct relationship between cutting height and the amount of roots a grass plant can maintain. Plants need sunlight to produce food through photosynthesis, Lowering the grass height means the leaf surface receives less sunlight, stunting energy production. This weakens the root system, making it harder for the grass to absorb water and nutrients from the soil.

In recent years, mowing height recommendations for home lawns have steadily increased.

Higher cut lawn grasses are generally more stress-tolerant, which is especially important when it gets hot and dry during summer. Taller grass plants are also denser, particularly on a lawn that’s properly fertilised and watered to keep it growing lush and healthy. This means they are much more effective at shading the soil surface, reducing the germination of weed seeds and the need for herbicide.

The leaf width of the turfgrass species and how it grows will determine the optimum cutting height. Grass species that have fine textured (narrow) leaf blades and grow almost horizontally to the ground are usually mowed shorter than an upright-growing grass with coarser (wider) leaf blades.

Every mowing session puts turfgrass under physiological stress, particularly if too much leaf tissue is cut off in one go. This can cause long-term damage to the turf – leaving it susceptible to other stressors such as insects, disease, drought, and sunscald.

Because mowing removes some of the leaf surface – the part responsible for photosynthesis – this triggers the grass into replacing lost tissue by transferring accumulated nutrients and energy into what remains of its leaves. But by doing this, the roots receive less energy, root growth decreases and, in some cases, stops completely until the leaf growth process is complete.

Higher mowing heights encourage a deeper root system, and gives the turf many advantages, such as: greater tolerance to drought and temperature changes, insects, disease and nematodes. Longer roots also make it easier for the grass to cope with poor soil conditions, nutrient deficiencies, and damage caused by human and animal traffic.

Generally, it’s best not to cut off more than one third of the grass blade. Most people find mowing once a week keeps the lawn growing healthily and evenly – unless the grass is a particularly slow-growing variety, in which case, a once-a-fortnight cut should be enough.