How Short Should You Cut Your Lawn in Hamilton? The Right Mowing Height for Summer

Every spring we pull up to lawns in Hamilton that have been mowed the same week as the neighbours’, by the same kind of mower, and look nothing alike. One is thick and green right to the edges. The other is patchy, a bit yellow, with clover and weeds coming through. Nine times out of ten the difference isn’t fertiliser or water. It’s the height the mower is set to.

Here is how short to cut a Hamilton lawn, why cutting it too short costs you, and when to lift the mower for summer.

The Short Answer

• Ryegrass lawns (most of Hamilton): 30 to 40mm in spring, lifting to 40 to 50mm through summer.
• Kikuyu lawns: 25 to 40mm, mowed often. Kikuyu is the one grass that likes being kept short.
• Shady areas and under trees: leave them at the top of the range, 50mm or so.
• New lawns: don’t mow until the grass is about 60mm tall, then take only the tips.

Not sure which grass you have? Here’s how to tell kikuyu from ryegrass. Plenty of Hamilton sections have both, with kikuyu taking over the sunny bits along the fence.

The One-Third Rule

The one rule that matters more than any number: never take off more than a third of the height in one mow.

If the lawn is 60mm tall, cut it to 40mm, not 20mm. If it’s been left for a month and is up around 100mm, don’t try to get it back in one go. Take it down to about 70mm, then again a few days later, then once more.

Grass feeds itself through the green leaf. Take most of the leaf off at once and the plant has to pull from its roots to grow back, which is exactly when the lawn starts to thin and the weeds move in.

What Cutting Too Short Does

Cutting low feels like good value. It looks tidy for longer and you think you can mow less often. In practice it works the other way.

• It goes yellow. The green part of the grass is at the top. Cut below it and you’re left looking at pale stems. That’s the yellow or straw-coloured look straight after a mow.
• It scalps. On bumps, high spots and the edges of paths the blades take the grass right down to the dirt. Those bare patches are where the weeds start.
• It lets weeds in. A thick lawn shades the soil so weed seed can’t get going. A thin one doesn’t. Clover and Onehunga weed both love a lawn that’s cut short.
• It browns off first in summer. Short grass means short roots and bare, hot soil. The scalped lawn is usually the first one in the street to go brown in January.
• It brings in moss. In the shady corners, a low cut on top of Hamilton’s wet winters is an open door for moss.

And it doesn’t save mowing. Grass that has been cut hard grows back fast to replace the leaf it lost, so you end up mowing just as often, on a weaker lawn.

Kikuyu Is the Exception

Kikuyu works differently. It grows its green leaf on top of thick runners, and if it’s left long it builds up a spongy mat of stems underneath. Then when it is finally cut, all that’s left is the brown-yellow mat.

So kikuyu is kept short, 25 to 40mm, but it has to be mowed often to stay that way. In a Hamilton summer that can mean every 7 to 10 days. A kikuyu lawn mowed short once a month will always look yellow afterwards. The answer isn’t to cut it higher, it’s to cut it more often.

When to Lift the Mower for Summer

For a ryegrass lawn, this is the time of year to start thinking about it. Spring growth is flat out right now, so 30 to 40mm is fine through October and November while the rain keeps coming. Then:

• Start of December: lift the mower one notch.
• January: lift it one more if it’s dry.
• March, once the autumn rain is back: drop it back down again.

Longer grass shades its own roots and holds the moisture in, so it stays green longer and needs less water. More on that in our post on watering your lawn in a Hamilton summer, including the sprinkler rules.

How to Check Your Mower Height

The numbers on the height lever don’t mean the same thing on every mower. A 3 on one brand can be a 5 on another. The easy way to find out what you’re actually cutting at:

1. Mow a strip of lawn at your normal setting.
2. Push a ruler straight down into the cut grass until it touches the soil.
3. Read off where the top of the grass sits. That’s your mowing height.

If it says 20mm, you’re cutting too short for a ryegrass lawn. Lift it a notch or two and measure again. While you’re there, check the blade. A blunt blade tears the grass instead of cutting it, and the torn tips go white and brown a day or two later, which looks a lot like scalping.

Frequently Asked Questions

How short should I cut my lawn in Hamilton?

Most Hamilton lawns are ryegrass, which looks and copes best at 30 to 50mm: around 30 to 40mm in spring and 40 to 50mm through summer. Kikuyu lawns are happiest shorter, 25 to 40mm, as long as they are mown often.

Is it better to leave grass longer in summer?

Yes, for a ryegrass lawn. Longer leaf shades the soil, holds moisture and helps the lawn stay green into January. Lift the mower a notch at the start of December and another in January.

Why did my lawn go yellow after I mowed it?

It was cut too short in one go. Either the mower is set too low, or the lawn was left long and then cut back hard, so the green leaf was taken off and only pale stems were left. Raise the mower and it will green up again in a week or two.

What is the one-third rule?

Never take off more than a third of the grass height in one mow. If your lawn is 60mm tall, cut it to no lower than 40mm. If it has got really long, bring it down over two or three mows a few days apart.

Does cutting the lawn short mean I can mow less often?

No. A lawn cut short grows back weaker and thinner, lets weeds in and browns off faster in dry weather. Mowing at the right height, more often, is what keeps a lawn thick.

Happy mowing!