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What is a mulch lawn mower?

A person uses a lawnmower to mulch grass

Want to mulch your lawn but don’t know where to start? We explain the ins and outs of a mulch lawn mower – and why you should use one

Using a mulch lawn mower is a fantastic way to improve your lawn’s quality. As well as recycling your garden’s waste, mulching increases the fertility of the soil by distributing grass clippings directly onto the lawn.

So what is a mulch lawn mower, and how does it work? Do you need a standalone machine or will a conversion kit attached to a cordless lawn mower do the job? We chatted to David Hedges-Gower, chair of The Lawn Association, to learn why mulch lawn mowers are such a good investment.

What is a mulch lawn mower?  

A mulch mower is essentially a mower designed to cut grass into smaller pieces, facilitating their incorporation into the lawn without creating a messy appearance,” Hedges-Gower explained to us.

The mechanics of a mulch lawn mower are pretty simple. Just like a regular lawn mower, a stream of air directs the grass up towards the mower blades – but a mulching mower’s blades have curved edges that allow the grass to be cut multiple times.

When the grass clippings fall they land straight onto the lawn, instead of being directed into a bag or out the side like a regular lawn mower. Now nicely shredded, they easily settle down among the growing grass.

A mulch mower can come in two forms: either as a standalone machine or as a mulching kit that attaches to and converts a pre-existing mower. The Karcher LMO 18-36 mower, for instance, comes with a separate mulching plug that blocks the grass bag chute, retaining the grass clippings inside the cutting deck so they can be further cut and then distributed automatically.

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Why should you use a mulch lawn mower? 

There are multiple benefits to using a mulch lawn mower: it improves the drainage and texture of your soil, stops thatch from occurring and provides you with a free source of lawn fertiliser. As David Hedges-Gower explains, “since grass blades contain about 70% water, using a mulch mower not only aids in dispersing clippings evenly but also reintroduces some moisture and a small amount of nutrients back into the lawn, as the grass clippings decompose.”

A close up of a persons gloved hands holding up mulched grass

On a personal level, using a mulch lawn mower is seriously efficient. There’s no need to rake and bag up your grass cuttings, and no compost piles or trips to the bin – a big help for those with mobility issues or decreased energy. The compact shape of a mulch mower also means it mows much closer to garden objects, so there’s less time devoted to trimming around your lawn’s edges.

When should you use a mulching lawn mower? 

It’s best to mulch your lawn in spring and summer when the grass is actively growing – a length of about 3cm is perfect. Mowing once a week and mulching twice a week during those warmer seasons will keep your lawn looking healthy.

While we won’t suggest mulching the grass in a heatwave, the decomposition of the grass clippings provides an added hit of moisture to the soil in hot weather. “This allows for mowing even in dry conditions while maintaining the lawn’s health and appearance,” David explained.

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Can you use a regular lawn mower for mulching? 

In theory, yes. As we mentioned above, there are plenty of mulching attachments and conversion kits available on the market, most of which will fit all manner of different lawn mowers. These conversion kits usually include a mulching blade and a mulch plug to block the grass collection chute.

It’s important to note that a standard mower’s blade can’t achieve the same level of cut as a mower made specifically for mulching. The latter’s blade is designed with a curve and a longer cutting edge to maximise airflow and grass-shredding ability. Moreover, a standalone mulching mower will have more power to shred organic matter, while a converted mower will be lighter duty.

If you already have a multipurpose lawn mower there may already be a mulching attachment included, so make sure you check before you buy a separate conversion kit.

When should I avoid using a mulch lawn mower?

There are a few occasions when you should avoid mulching:

Overly long grass

If the grass is too long when you mulch, the layer of grass clippings left on the soil will be too dense. This blocks airflow with the soil, interferes with decomposition and can smother your lawn. Mulch lawn mowers work best when the grass is around 3cm tall, but no taller than 8cm.

Wet grass  

Wet grass – and soil – can cause heavier lawn mowers to sink downward while performing. This brings additional moisture into the clippings, causing them to clump up and clog the machine, as well as leaving chunks of clippings on the lawn instead of a light scattering. As such, don’t mulch if your grass is wet from rainfall or if you’ve just watered it.

Too many weeds

If you have weeds in the garden and on your lawn, those weeds will be mulched and distributed throughout the lawn. The best way to get around this is to weed thoroughly (and properly dispose of them) before using the mulch mower. 

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