Lawn mowing is one of the most important tasks when it comes to lawn care. As lawn care experts, Green Man Lawn Care can do everything else, but lawn mowing is the responsibility of our customers.

“Listening to our advice and employing the correct lawn mowing techniques will help you and your lawn gain more benefit from our treatments”

The key to a good lawn mowing regime is “little and often” – The more you cut a lawn, whilst taking the minimal amount of growth off from the top, the healthier and thicker the grass plants will grow, leading to a thicker, healthier looking sward of grass.

A thick lawn also makes it harder for moss and weeds to take hold.

The five most important factors are:

  1. The height of the lawn mowing
  2. The frequency of the lawn mowing
  3. Ensuring the lawn mower blade is sharp
  4. The speed at which the lawn mower travels over the lawn
  5. Collecting the clippings

The Height of the Cut

The ideal height of the grass plants in a lawn is between 1.5″ and 2″. The plant should never grow beyond 3″, and should always be cut back down to the same height, ensuring that no more than a third of the height of the plant is removed.

Why is this so important?

The grass plant differs from most other varieties of plants as it has evolved to grow new leaves from the bottom of the plant, rather than from the leaf stems. This is because grass is the primary feed for grazing animals such as cows and sheep. These animals, continually eat the grass plant leaves, leaving enough leaves on the plant for it to continue growing and produce new growth. If the animals were to bite too much of the grass plant off in one go, it will leave the plant without leaves.

Plants require leaves to photosynthesise. Photosynthesis is a plants way of making energy to live. If a plant has no leaves, it can’t photosynthesise, and its only option is to enter a survival mode. This survival mode forces the grass plant to use up its energy storage in an attempt to grow a single leaf.

This single leaf is enough for it to start photosynthesising again, but the plant has used up a lot of its stored energy in doing so. As it photosynthesises, it will start to store energy again, but the likelihood is, the new single leaf will once again be cut too low. This cycle of cutting too much off the plant in one lawn mowing session causes the plant to remain sparse of blades, leaving the overall lawn looking sparse of growth.

Cutting too short has other disadvantages. Grass is comprised mostly of water which is stored around the plant and mostly in the blades. Cutting the grass plant too short results in the plant drying out very quickly. As it is now in survival mode, it doesn’t have the energy to replenish the lost water quickly, resulting in a very dry and unhealthy lawn.

Therefore, the key to a good cutting height is to never take more than a third of the plant’s height off when mowing. By doing so, you will leave plant with the ability to continue photosynthesising, allowing it maintain a nice green colour, and use its stored energy to produce healthier new leaves.

The following diagrams show the results from cutting at different heights. The black horizontal line represents the cutting height.

The diagram above shows what happens to the grass plant if you don’t cut your lawn ferquently enough, taking far too much of the plan off at each cut.

The first cut takes over two thirds of the plant height off the plant, resulting in the grass plant entering survival mode. Notice by the second cut, the plant has only produced one new leaf as it struggles to continue to photosynthesise. As the plant ends up with just a stem showing, the lawn can look very brown as there is hardly any green leaf matter.

The diagram above shows what happens when you increase the frequency of yor lawn mowing, taking less off than you would from the first diagram.

The first cut takes off half of the grass plant, leaving it with two small amount of leave. The plant will start to use up energy from its storage, while trying to photosynthesise to grow more grass blades. However, at the second cut, half of the plant is once again cut off, rendering the plant with very little leave to photosynthesise. This method will result in a sparse lawn.

The diagram above shows what happens when you mow your lawn frequently, taking no more than a third off at each cut.

The first cut takes off around a third of the plants height. This leaves a sufficient amount of leaf matter remaining for the plant to photosynthesise, whilst using its excess energy stores to grow new leaves from the base of the plant. As this method is repeated, the plants will get thicker and thicker, resulting in a very green and healthy looking lawn. Cutting at the right height also allows the grass plant to retain moisture for a longer period of time.

The frequency of the lawn mowing

One of the biggest questions we get asked is:

“How often should I cut my lawn?”

The answer is

“when it needs cutting”

In order to know when best to cut a lawn, we need to refer to our first rule of lawn mowing regarding the cutting height (see above). Remember, we should never really take more than a third of the plant off when lawn mowing. Therefore, it is best to base the mowing requirements on the growth of the grass plant following its last cut. If your last cut left the height of the grass plants at around 2 inches, then your next cut should be before the grass plant has grown by 1 inch, to 3 inches.

As grass grows quicker during the warmer and wetter months, it’s important to keep on top of the lawn mowing at this time of year. For information on when the grass plant grows throughout the year, click here.

It is also important to remember that there is no good or bad time of year to cut a lawn. The grass plant will continue to grow as long as air and ground temperatures remain above 8 degrees Celsius, and there is sufficient water in the soil. During unusually warm autumns and winters, it is common to find that the grass plant continues to grow throughout the season, so it is important to maintain some form of cutting regime to prevent the grass plants shadowing each other out.

When NOT to mow a lawn

There are times when a lawn must not be cut.

During periods of drought, the grass plant must be able to preserve as much moisture as possible. Water is carried around the plant through it’s vascular system. When a lawn is cut, the individual blades of grass are sliced, leaving an area where moisture can escape. During times of drought, a grass plant can lose all of its moisture after just one cut. During the spring and summer, the best time to mow a lawn is in the morning or in the evening. Mowing a lawn in the midday sun will severely damage the grass plants and reduce the overall health of the lawn.

Cutting during frosts is equally as bad. As the air temperature around the plant reaches a freezing point, the moisture in the grass plant will also start to freeze. Cutting a grass plant whilst it is frozen will irreparably damage the fibres of the plant.

Ensure your lawn mower blade is sharp

Lawn mower blades need to be sharp to ensure they cleanly slice through the leaves of the grass plants. Each time you mow your lawn, the gras plants leaves are opened up, allowing moisture to escape. A clean slice allows the cut to close up quickly, reducing moisture loss.

A blunt mower blade will rip and tear the grass plants leaves, often exposing the fibres, and allowing too much moisture loss. 

Above: A blunt mower blade will rip the grass plant’s leaves, rather than cleanly slicing them.

The speed at which the mower travels over the lawn

It’s important that the lawn mower doesn’t travel too quickly over the lawn as this can also cause the blade to rip the grass plant’s leaves. Some mowers are self powered and will have a maximum speed at which they can travel. Pedestrian powered lawn mowers however can be pushed quicker than they are designed to travel, which is where problems may start to occur. A good speed is around a stead walking speed.

Pushing it too fast is far worse than pushing it too slowly as the blade will not have a chance to cleanly slice each leaf of the grass plan and will also effect the rate at which it picks up the grass clippings.

Above: The blades needs to be able to cleanly slice each grass plant to prevent it ripping them.

Collecting the clippings

Above: Grass clippings left on a lawn will cause damage to the grass plants and will create thatch.

Lawn Mower Type

There are two different types of lawn mower, and they are defined by their cutting action:

  1. Cylinder mower
  2. Rotary mower

Cylinder

Cylinder mowers have a front and rear roller with a bed knife set at the desired cutting height, and a horizontal reel fitted with blades which push the grass onto the bedknife and cut it with a scissor action. The number of blades on the reel combined with the forward speed, dictate how fine the cutting quality will be. This is because of the number of cuts per metre increases with the number of blades, from the lowest of four blades giving fifty to sixty cuts per metre, up to the professional greens mowers with twelve blades giving five hundred or more cuts per metre.

 

 Above: The cutting action of a cylinder mower. The blade slices the grass blade using a scissor action.

Cylinder mowers are very much the only option for the better quality lawns and sports surfaces such as golf and bowling greens, as the cut is so much cleaner. This is not only because it looks so much better, but even more importantly the grass plant recovers more quickly as the rotary blade bruises and tears the leaf, giving a brownish appearance and healing up much more slowly. The other main advantage with cylinder mowers is the light rolling action which keeps the lawn surface firmer and smoother.

Cylinder mowers are not very forgiving in comparison to rotary mowers. If a lawn is left too long without cutting, a cylinder mower will struggle. A cylinder mower demands a much stricter cutting regime.

 

Above: A cylinder mower attachment

Cylinder mowers can be fitted with a variety of brushing a raking aids, either in front or behind the front roller, in this case a brush to lift the grass blades for cutting, and clear worm casts.
Cylinder mowers also pick up and throw the grass into the collection box much more efficiently than rotaries, even in wet conditions. The ground has to be reasonably level, with no steep slopes, for any cylinder mower to work properly, and the lawn has to be cut regularly as they do not cope very well with long grass.
A cylinder mower with four or five blades will offer a perfectly acceptable lawn mower for every day use, with any increase in the number of blades giving a correspondingly better quality of finish. This has to be in conjunction with mowing more regularly as the blades being closer together means they cannot cope with longer grass, which results in what we call ribbing as the blades try to chew their way through the sward. This also puts strain on the mowers moving parts resulting in expensive repair bills.

Rotary

Rotary mowers are by far the most common lawn mower found in our customer’s sheds. Rotary mowers work by spinning a blade at high velocity over the surface of the lawn. The blade sharp at both ends, and the cuts the grass with a slicing action.

 

Above: The rotary mower blade slices the blade

 

Above: The underneath of a rotary mower. The mower shown above requires cleaning as there is a build up grass around the chassis

Above: The collector box of a rotary mower. The spinning blade creates a vacuum, and sucks the grass clippings off the surface of the lawn. The spinning action then throws the grass in to the collection box.

Which lawn mower should I use?

This really depends on a combination of preference and praticality. Rotary mowers are much less forgiving than cylinder mowers. They can be used on wetter lawns and can cope with a higher grass growth. If it’s quality you’re after, then a cyclinder mower will be better, but it’s important that you maintain a strict lawn mowing regime.

Should I use a strimmer?

Strimmers are not designed for cutting lawns. Strimmers work by spinning a plastic string at high velocity, which chops the grass plants or other green material it is targeting. Strimming is more commonly used on rough grounds where there is requirement for a healthy looking lawn. We would highly advise our customers to not use a strimmer to mow their lawn.

Above: A strimmer being used on rough grass – strimmers must not be used on lawns!

Collecting grass clippings is important. Grass clippings lead to a build up of thatch on the lawn.

Clippings that are left on the lawn will shade the grass, reducing the amount of light that reaches the lawn. If the cycle of leaving the clippings on the lawn is repeated, the constant shading of the grass plants will lead to yellowing or dead patches throughout the lawn.

Clippings that shade the grass plants can also increase the amount of fungal disease.

What can happen if I don't follow this lawn mowing advice?

As lawn mowing plays such a large role in lawn care, your lawn can look weak and sparse. If left to grow too long, leading grass plants will start to shadow out surrounding grass plants, creating a sparse and often patchy lawn.