How to sharpen lawn mower blades safely and easily

Ground level lokk at cutting long grass with mower slightly out of focus
(Image credit: Getty Images)

If you’re a DIY gardener you’ll want to know how to sharpen lawn mower blades. Maintaining a sharp clean blade goes a long way to making sure that your grass stays neat and green.  

Whether you are using an electric mower, a cordless lawn mower or one of the best petrol lawn mowers they all need looking after to make sure that they keep your lawn in tip top condition. Here we tell you why, when and how to look after your lawn mower blades. 

How to sharpen lawn mower blades: why they need a little love 

Over time your lawn mower blades will dull and become less effective at cutting your grass. There’s general wear and tear and then there’s nasty nicks you can get from hitting stones or other hard objects when mowing.

A dull blade will rip and tear the blades of grass instead of giving a clean cut which will leave the grass more susceptible to disease and lead to yellowing as it takes longer to recover. What's more, the harder the grass is to cut, the harder your lawnmower will have to work, which can shorten the lifespan of the mower. 

How do I know if my lawn mower blade is sharp or blunt? 

If you have been regularly using your lawnmower for a few years without any maintenance on the blades then it's probably time to sharpen them. If the blade is not giving a neat even finish this is another sign that they need sharpening.

One obvious way is to look at and feel the blade. If it has chunks or nicks on the edge of the blade then these need to be dealt with. If the edge of the blade looks rounded and dull, it is time to give it a sharpening. But, do not forget to make sure that all safety precautions are taken.  

Can I sharpen my lawn mower blades without taking them off? 

Yes you can, but it is recommended that you remove the blade if at all possible. If you don’t have the tools to remove the blade then you will need to secure the blade as best as possible in situ. 

Before you start don’t forget to unplug, remove spark plug or batteries, to make sure no power is getting to the mower. You can use strong nylon string to wrap around the blades and tie around the body to keep in place. Or use a block of wood to hold the blade in place.

Lawnmower blades are not razor sharp but it is a good idea to wear heavy-duty gardening gloves so you can hold the blade steady if you need to. 

Can you sharpen a lawn mower blade by hand? 

If you don’t have a power tool to help sharpen a mower blade you can use a metal file like the Draper Flat File from Amazon. You can sharpen by hand without removing the blade, but ideally you want to remove the blade and hold it in a vice.

Check the manufacturer's instructions on removing a blade, but you will typically need a spanner or the right size socket spanner to undo the central bolt to remove it. Place your blade in a vice and push the file across the blade from the outside edge into the middle until done. Do not create a razor sharp edge as this will damage easily.  

What is the best tool to sharpen mower blades? 

A flat metal file is a great choice for sharpening blades; they are inexpensive and simple to use. But If you're looking for a little more assistance a drill and a multi purpose blade sharpener attachment like the Multi-Sharp Multi-Purpose Blade Sharpener from Amazon are a good choice.

This type of attachment features a circular stone that is shaped to create the right cutting angle on a blade. You'll need to place it in the chuck of a drill and make sure it's fully tightened. You can use the outside of the sharpener to get rid of heavy nicks and dents. Then place the sharpener on the blade at the right angle – see manufacturer's instructions – and power up the drill and move the sharpener back and forth along the blade until done. Repeat on the other blade edge to finish.  

Gloved hand holding lawnmower blade and sharpening blade with Multi-Purpose Blade Sharpenerwith

Make sure that the blade won't spin when using a blade sharpener by holding a block of wood in place. Remember to wear heavy-duty gardening gloves (Image credit: Steven Jenkins)

Should I get a professional to sharpen my lawn mower blade? 

If you are not confident sharpening your lawn mower blade, or do not have the tools to do the job, you can get a professional to take on the job.

The cost will depend on whether you are removing the blade yourself and taking it to a professional or they are coming to you to do the job. Expect to pay £5-£10 if you are taking the blade to a professional to be sharpened. If you are using an online service where you need to send the blade away add around an extra £5-£7 for postage.

If you need to take your lawnmower to a professional to get the blades sharpened expect to pay around £15. With a newly sharpened blade you will be able to cut long grass and get a neat finish on your lawn. 

How often should I sharpen my lawn mower blades? 

This depends on how often you use your lawnmower and the size of your lawn. If you have a small suburban garden that gets cut four or times a season, then once a year should be enough. If you have a large garden and cut more regularly, then at least twice a year should suffice.

Steve Jenkins

Steve is Homebuilding & Renovating's DIY content editor, and has been a writer and editor for two decades. He is an avid DIYer with over 20 years of experience in transforming and renovating homes. He specialises in painting and decorating, but has strong all-round building skills, having previously worked in the industry for 10 years.