What height should you mow your lawn?

Most people set the mower once when they buy it and never touch it again, and then wonder why the lawn thins out and the weeds move in. Height is one of the few lawn decisions you make every single time you mow, and it is worth about 5 seconds of thought.

Why cutting it too low backfires

The leaf is how the grass feeds itself. Take too much of it off and the plant has to pull on its reserves to grow it back, so it puts energy into leaf instead of into root, and a lawn with a shallow root system dries out faster and needs more water, not less.

Scalping does a second thing that matters more than people realise. It exposes bare soil to full sun, and bare soil in the light is exactly the condition a weed seed is waiting for. Thick grass at a sensible height shades the soil and smothers most of them without a spray. That is the cheapest weed control there is.

So the short lawn that was going to save you mowing ends up costing you water, fertiliser and weed spray instead.

The heights, by grass type

These are the usual ranges rather than laws, and the general rule is to run at the lower end through the growing season if you like it tight, and lift it towards the top of the range going into summer or in a shady spot.

• Couch. The lowest of the three, around 10 to 25mm. It is built for a close cut and it looks its best that way. Take it much below that and it goes patchy.
• Kikuyu. Around 25 to 50mm. It grows fast and it will take a low cut, but it recovers better and looks thicker at the higher end.
• Buffalo. Around 35 to 50mm, and higher again if it is in shade. It has a broad soft leaf and it wants length to look right. Buffalo cut short is the classic way to ruin one.

If you have no idea which one you have, take a photo and bring it in and we will have a look. Most Strathalbyn back lawns are one of those three.

The one rule that matters more than the number

Never take off more than a third of the leaf in one cut.

If it has got away from you over a wet fortnight, don't drop the mower to where you want it and make one pass. Take a third off, leave it four or five days, then take another third. It takes two goes instead of one and the lawn does not go yellow and sulk for a month, which is what happens when you take half the plant off in one afternoon.

Two things that undo a good height

A blunt blade. A sharp blade cuts the leaf. A blunt one tears it, and a torn leaf tip goes brown and browns off the whole lawn a few days after you mow. If the tips look ragged and whitish rather than cleanly cut, that is the blade. They are cheap to replace and it is a 10 minute job.

Mowing wet grass. It clumps, it tears, it packs under the deck and the cut is uneven. If you can wait for it to dry, wait.

And leave the clippings on unless they are lying in clumps. They break back down and return a useful amount of nitrogen to the lawn, which is free fertiliser you would otherwise be bagging up and putting in the bin.

Shop related products

• Jak Max Masport swing back blades. Blade and bolt set for 18 inch rear catcher models, and the single cheapest thing you can do for how the lawn looks.
• Jak Max 10W30 4 Stroke Oil 1L. For the annual service, which most mowers never get.
• Brunnings Green Up Lawn Food 2.5kg. Feeds and greens without pushing so much top growth that you are mowing twice a week.
• Brunnings Tough Lawn Seed 1kg. For the thin patches that a low cut has opened up.

More in the Brunnings range, outdoor power equipment and the garden centre.

Did you know we also stock mower blades and belts for a range of models in the shop, along with Cyclone and Gardenmaster garden tools. They aren't all on the website, so bring the old blade in or give us a ring on (08) 8536 4333 and we will match it up.

More from the garden

• How to stop fertiliser and water running off your lawn
• How to plant a kikuyu lawn in South Australia

Still learning, and I am firmly of the view that a sharp blade fixes more lawns than any bag of anything.

Cheers,
Candeece