Question: Lawn cutting heights?

By | 18/10/2019
A lawn mower which can adjust the lawn cutting heights

I received this interesting question from Craig in October 2019. He asks an interesting question about lawn cutting heights during the year.

Hi Kris,

I suspect this is covered on your website, but I’m afraid to say I can’t find it! [Edit: I have covered it here]

I have been experimenting with lawn height this year as we felt our lawn was suffering from being cut too short in the past (by our gardener). Circumstances have meant we now cut the lawn and 2019 was our first season. We took the decision to cut it much higher (around 50mm) and the lawn has seemed much healthier… however, I don’t know what the optimum height is and have realised this could take years of experimentation.

Also, I was wondering whether there is any benefit in cutting the lawn to different lengths at different times in the season. I note, I did find the article that said lift the blades to about 30mm in autumn, but as we are cutting the grass higher than this already I’m not sure where that leaves us.

Our lawn was turfed about 10 years ago, is on a south facing tiered garden. Generally it is on clay although the tiers do seem to facilitate drainage. We apply minimal treatments to the lawn having fed it last autumn and early this summer. I have taken to hand weeding for now. We scarified the lawn quite heavily last autumn with a metal blades cassette fitted to the scarifier and followed this with a light scarification in the spring (with the spring tines cassette).

We look forward to your advice.

Kind regards,
Craig

How high should you mow your lawn?

Hi Craig,

Thanks for your question. Questions about lawn cutting heights are very common from my lawn care customers.

Example of lawn cutting heights on my test lawn
Test lawn grass is kept long all year round.

Domestic lawns are very different to sports turf such as a bowling greens or golf courses. Sports grass needs to be smooth enough to roll a ball along. This requires a special low-growing turf grass which is happy mown short.

Domestic lawns are rarely sown with this species of grass. As you have found out, our lawn grasses in the UK look much better when left to grow a little longer.

But how long? Well, at home I mow my own test lawn on the very top setting of my Honda mower. This works out to be around 70mm. I keep this level all year round. But why?

Reasons for higher lawn cutting heights

There are a huge number of benefits gained from raising your mower blades and letting your lawn grow longer.

Your grass will be healthier

Long grass is healthy grass. It can absorb more sunlight for making food. It can put down stronger roots, withstand disease, be harder wearing and recover from wear more quickly.

You will increase biodiversity

Just raising your lawn blades a few centimetres can dramatically increase biodiversity in your lawn. More beetles and insects, means more birds and less pests. An increase in biodiversity will mean a healthier lawn and garden.

It will hide worm casts

In the wetter months of autumn and winter, worm casts can be a problem. Worms are fantastic for your lawn but their casts can be a nuisance. The easy way to reduce their visibility is to let your grass grow longer. The casts will not be noticed and your lawn will look healthy.

Your lawn will have less weeds and moss

Weed seeds germinate much more easily on exposed soil. If your lawn is mown short and you can see patches of soil, weeds will take advantage. A long lawn which takes up all of the soil space does not allow weeds seeds to germinate. It is also strong enough to out compete young weeds and leaves no space for moss to creep in.

Your lawn will improve drought resistance

Long grass puts down a much deeper root system. It also holds more water and a thicker cover over the soil reduces transpiration and moisture loss. Longer grass also captures more morning dew. Longer lawns stay greener for longer during dry weather periods. Keep your grass long all year round and it will stay greener for longer during the summer.

You can mow in much better stripes

For those of you who love the look of a beautifully striped lawn, long grass is the key. Stripes are created by bending over the grass blades in different directions. Longer blades are easier to bend and look much more pronounced. Be the envy of your neighbours and stripe your lawn like a professional.

You wont need to mow your lawn as much

Longer grass is less stressed. If you keep stressing your grass by mowing all of the leaves off, it has to rush to replace these leaves to survive. A thick, long lawn does not grow as quickly as a short lawn. Try it, it will look better and be less work for you.

Lawn cutting heights during the winter?

If you are not brave enough to take your mower blade right to the top all year round then certainly do so during the winter. The lower light levels during the UK’s colder months mean the grass struggles to perform photosynthesis (make food using sunlight). A longer leaf will help your grass during these difficult times. You can always bring the length back to your usual levels gradually in the spring.

In summary, How high should a UK lawn be mown?

To summarise, I would never recommend mowing any UK lawn to lower than 40mm. For the majority of lawns keep your height to at least 50mm during the summer, and to the very top of your mower during the winter. This will help your lawn will look lush and green all year round.

Thanks for reading!

Kris Lord

A beautiful lawn in Whipton, Exeter
A beautiful longer lawn in Whipton, Exeter
All images in the article were from The Lawn Man’s media archive, not sent in by the questioner.

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