What Height Should You Cut Your Grass in the UK? Follow The Golden ‘Rule of Thirds’

by Daniel Hunter

I’m going to show you how high to cut your grass to keep your lawn looking mint all year long.

Mowing at the right height will affect how often you mow and it’ll prevent you from ever cutting grass to short.

What’s The Best Mowing Height?

best mowing height

The best mowing height achieves two things. It;

  1. Creates an epic look, while at the same time,
  2. Allows the grass to keep enough leaf to maintain healthy function

It’s not a ‘one size fits all’ solution though. The ideal cutting height depends on the following;

The Types of Grass in Your Lawn

Different grass types grow quicker than others. While some grasses look awesome when mown very short.

For example, rye grasses grow faster than bents and fescues. They’re also healthier and look better when mown between 25mm and 35mm.

While bent and fescue grasses are much slower growers. They look fantastic when mown between 6mm – 15mm.

Your Lawns Function

How you use your lawn should dictate the type of grasses used in it. And as such, the height at which you cut it.

If you have a family and use your lawn for play, then ryegrass will stand up to wear and tear. It’s best to mow a little higher as having plenty of leaf will help the grass recover after use.

Ornamental lawns meant for only admiring should only contain bents and fescues. You can mow these very short but that means they don’t stand up well to heavy use.

Your Personal Preference

You might prefer the look of your lawn with the grass on the higher side. If you have a roller on your lawn mower, you might only want the grass high enough to create a bold, striped finish.

Or you might like a close cut.

Cut your lawn at the length you like it. That said, be mindful of the types of grasses your lawn contains and how you use it. If you like a short lawn but the kids spend their days rolling around on it, it might not stand up to that kind of wear. In which case, you’ll need to compromise.

Type of Lawn Mower You Own

The type of lawnmower you own will also play a part in how high you mow. Although many people don’t even consider it as a factor.

Rotary mowers are the most common type. They’re cheaper than cylinder mowers and perform better on uneven lawns. That said, their spinning blades don’t cut as clean as the scissor action of a cylinder mower.

Rotary mowers are a bit more brutal in the way they cut the grass. As such, it’s best to keep it a little higher to help it recover between cuts.

The clean cut of a cylinder mower is much gentler on the grass. So you can get away with mowing on a shorter setting as the grass won’t have as much recovering to do afterwards.

Lawn Mower Height Setting Heights: A General Guide

setting the height on a lawn mower

The tables below show my personal mowing height recommendations, based on;

  1. Lawn type (family or formal)
  2. The time of year, and
  3. The type of lawn mower you own

As I said, these are my preferences. If you like your lawn longer or shorter, knock yourself out, don’t let me stop you.

Family Lawn Mowing Heights

Mower TypeTime of YearMowing Height (mm)
RotarySpring20 – 25
Summer25 – 35
Autumn20 – 30
Winter30 – 40
CylinderSpring15 – 20
Summer20 – 25
Autumn20 – 25
Winter25 – 30

Almost all family lawns contain ryegrass due to its ability to cope with wear and tear. It copes better and appears thicker when you keep it a little longer. Ryegrass also grows quicker than bents and fescues which means regular mowing.

Any grass seed mix which contains ryegrass is a ‘family’ or ‘utility’ blend. Even if it’s mixed with bents and fescues. That’s not to say you can’t create a beauty of a lawn though. Some of the best looking lawns I’ve ever seen are ryegrass blends.

Ornamental Lawn Mowing Heights

Mower TypeTime of YearMowing Height (mm)
RotarySpring20 – 25
Summer20 – 25
Autumn20 – 25
Winter20 – 25
CylinderSpring10 – 15
Summer15 – 20
Autumn10 – 15
Winter20 – 25

True ornamental lawns don’t contain ryegrass, only contain bents and fescues. They tolerate very close mowing and look phenominal with their dense, bristley covering.

That said, they’re very labour intensive to keep. Only consider an ornamental lawn if you have the time and knowledge to look after it.

ALWAYS Cut Your Grass Using The ‘Rule of Thirds’

A golden rule for mowing your lawn is to never cut off more than a third of its current height. We call it the rule of thirds. If you’re learning how to mow the lawn, stick to this rule like glue and you’ll never mow too short again.

Why the Rule of Thirds is So Important

Grass uses its leaves to trap sunlight to use as energy, in very much the same way we use solar panels to heat our houses. It uses this energy to power photosynthesis (remember that from school?) and the production of food.

It stores that food (and water) in its leaves to use when times get tough. During the heat of the summer and cold of the winter for example.

Every time you cut the grass, you take away part of that food and water supply. You also reduce the size of its leaf and as a result, the amount of sunlight it’s able to trap to produce more.

Grass copes well when you remove up to a third of its leaf. In fact, it releases a hormone which kickstarts new growth, creating a thicker, denser lawn.

But when you cut 50%, 60%, 70% off the length, you rob it of 50%, 60%, 70% of its food and water supply. You also reduce its capacity to produce more food by such an extent that the grass won’t be able to repair itself.

As a result, the grass weakens, often turning yellow or brown. That’s when weeds and moss start to creep in, followed by signs of disease.

But What if My Grass is Long? How Do I Get it Down?

You often find this happens when you come back off holiday and your lawn has grown taller than your house. Your grass is often longer as we come out of winter into the spring.

If this is the case, read my article on how to cut long grass for a step-by-step guide.

But the rule of thirds still applies here.

Cut your grass, removing no more than a third. Then let it grow by 5mm and cut it again, removing a third. Let it grow 5mm and cut again. Keep going until your lawn is at the height you want it. It usually only takes 4-5 cuts.

How to Maintain Your Lawn At Your Favourite Height

Now you’ve got your lawn down to your favourite mowing height, never let it grow by more than a third.

So in this case with a preferred height of 25mm, you’d never let the grass grow over 35mm. The weather will dictate how often you mow. It could take 3 days to reach 35mm, it could take a week, so mow as often as growth dictates.

That said, the shorter you like your lawn, the more often you’ll need to mow.

For example, if you like a formal cut at 8mm, you’ll need to mow before or as the grass reaches 12mm. This could mean mowing every 1-2 days if growth dictates.

At the End of The Day How High You Cut Your Grass is Up to You

If you like your grass quite tall, no worries. If you like it putting green short, good for you. If you like it tall enough to create an epic striped finish, awesome.

My guide is only that, a guide (although it’s a good guide based on years of experience!)

As long as you;

  1. Mow at a sensible height based on the season and growing conditions
  2. Mow often enough to maintain your lawn at your preferred height, and
  3. Never cut off more than a third of the grass’ current length at a time

Your lawn will stay in good health and look awesome.

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