How to Kill and Prevent Lawn Moss

Written by Daniel Woodley. Reviewed by Elizabeth Smith. Published to Lawn Care on 9th January 2020. Updated: 22nd February 2023.

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Moss is an unsightly green and uneven mass I’ve seen plague many lawns in the UK.

The flowerless plant forms thick chunks that contain millions of spores which allow the plant to spread quickly in shaded and damp areas of the garden.

Moss is opportunistic and I’ve witnessed it thrive on compacted soil, boggy lawns and in areas that receive little direct sunlight.

My name is Daniel and here’s my guide to removing and preventing lawn moss, which is based on over 18 years of experience.

Step 1) Check For Drainage Issues (a quick case study)

Take a look at the photo below:

This lawn is bathed in plenty of sunlight – at least 4 hours a day in the winter and much more in the summer; that’s plenty for grass to thrive. 

I checked the soil nutrient levels and there were no issues, the pH levels and amounts of Potassium, Phosphorous and Nitrogen were all within norms. 

The ground was neither compacted nor suffering from excessive foot traffic, neither was the grass cut too short. Yet, 90% of this “lawn” is in fact, moss.  

On closer inspection, one can see that the four sides of this lawn area are elevated. Rainwater, especially during the winter, flows and collects in this area where it pools. 

While this isn’t obvious in the summer, come winter the entire area is damp and boggy. The lowest point of the lawn holds around an inch of surface water for several days after heavy rainfall. This makes the area a perfect moss breeding ground, especially in the rainy season. 

No amount of chemicals, sunlight, grass seed or added nutrients will prevent this moss from returning, the issue here is drainage or to be more precise; lack of drainage.

After doing a survey of the ground, I advised the owner of this garden to install a drainage solution which included a French drain.

If you have a moss problem in your lawn, first check for any drainage issues.

The FlowerPotMan website has published a guide to diagnosing and fixing garden drainage issues. Go check it out, it’s a great read.

Step 2) Increase Sunlight Into The Garden

Common lawn grasses require a minimum of between 4 and 6 hours a day of sunlight. Any less than this and the grass will thin out and mosses and weeds will start to take over.

When designing a garden, I always pay attention to areas that receive very little sunlight. Instead of sowing seed or laying turf, I would consider creating a flower border, a patio, path, decking or other area made from materials that don’t require sunlight to thrive.

The next step is to maximise the amount of light coming into the garden, do consider both indirect and direct sunlight.

I’ve found that this can often be achieved by:

• Installing shorter fence panels at the boundary
• Using trellis instead of solid fence panels
• Using a tree lopper to cut back and top shrubs
• Reducing the height and spread of any trees nearby
• Relocating sheds, if possible

Moss will thrive in shaded areas where grass doesn’t grow well, and if you’re serious about dealing with moss, you’ll need to increase the amount of sunlight coming into the garden, if you can.

I know from years of testing and experimenting that one cannot compensate for the lack of light by using more grass seed, turfing or over-fertilizing the lawn. 

Grass requires light for photosynthesis and without it, the grass thins out, and moss takes over.

Step 3) Conduct a Soil Nutrient and PH Test

This step is optional, but if your lawn won’t grow and moss keeps taking over, consider taking a soil sample for a nutrient and pH test.

Like any plant that grows in the garden, grass requires nutrients and will thrive if sown in soil with the correct pH level.

Too much or too little of the key nutrients and the grass may struggle to grow, leading to bare patches where moss will take over.

A test can be performed to determine the levels of the key nutrients currently in the soil; Potassium, Phosphorous and Nitrogen. The test should also reveal the pH level, or acidity of the soil. 

Based upon the results, you can then add manure, topsoil, sand and fertilisers until your soil contains the optimal levels of the key nutrients and is within the normal pH range.

Taking this step improves the quality of the grass and helps to stop lawn moss from forming and spreading.

DIY soil test kits are available to buy online, or you can send a sample to the Royal Horticultural Society, who, for a fee, will send you the results and details about how to improve the quality of the soil.

My Experience With Soil Test Kits

I previously reviewed “home” soil test kits, see what I thought of the results.

In short; they worked very well at determining soil deficiencies and were cheap and easy to use.

Step 4) Kill and Remove Any Existing Lawn Moss

In my opinion, there are only two products good at killing and removing lawn moss:

Option 1 – The Traditional Method

The traditional method of lawn moss eradication involves treating the entire lawn with iron sulphate and waiting for the lawn moss to die and turn black.

The dead matter can then be pulled out, either manually with a rake or with an electric scarifier.

Following this, the lawn should be overseeded with new grass seed and topped with nutrient-rich soil that should be brushed in.

Option 1 is a popular method that works well in small gardens. For larger areas, the method requires a lot of hard work and option 2 may be preferable.

Based on my experience, I feel the best time to start option 1 is either in the spring or autumn when the new grass is actively growing.

Option 2 – The Organic “No Rake” Method

Option 2 is to use an organic moss killer that also contains a bacteria that consumes the dead moss, dead grass and decayed thatch that collects at the base of the lawn.

Postscript update: Read my full review of MO Bacter for lawn moss here.

This product is known as a “no rake” moss killer.

There are several products on sale and they are very similar.

I found them easy to use, all I did was dilute the granules with water and applied to the lawn moss with a watering can.

As the moss was killed off and consumed by the bacteria, I noticed the existing grass spread into the void and I overseeded it to give it a helping hand. 

While the “no rake” products are easy to use and cheap, I’ve found that one application is rarely sufficient and the last time I used it, I applied it twice, 4 weeks apart.

I found that the best time to start option 2 is also in the spring or autumn when the grass is actively growing.

 Moss Rake/Scarifier

Designed specifically for removing moss and thatch from lawns, the hooks on this roller grip the moss and tear it from the lawn. The grass is left untouched and is free to grow into the space created. This is the best moss rake we’ve tested

You’ll also need to purchase the pole/handle for this roller head.

Step 5) Choose Shade Tolerant Grass Seed

Shade-tolerant grass seeds have been specifically cultivated to thrive in areas with limited sunlight.

Unfortunately, there is a catch.

I know from experience in my garden that grass which copes well in shaded gardens usually struggles with foot traffic.

In short; shade tolerant grasses are often best used on ornamental lawns rather than practical lawns.

I Recommend:

I’ve done my homework and after testing different seeds over the years, I feel the best ones for shaded areas are:

Red Fescue – A fine-leaved ornamental grass that is well-known for its ability to thrive in shaded areas.

Creeping Red Fescue – Also known as Strong Fescue, this grass spreads horizontally via rhizomes. While it doesn’t thrive in cold weather conditions and may provide only sparse coverage in winter, expect good wide and thick coverage in the summer, even in shaded areas.

Bentgrass –  Expect good thick lawn coverage, even in cooler climates and in shaded gardens, but only where there’s good drainage and soil aeration. 

Perennial Ryegrass – A great companion or “filler” grass that fills in gaps and sparse areas often created by shade-tolerant grasses.

As you can see, one type of grass seed is almost never enough to provide good, thick coverage for shaded gardens in all conditions.

Some types of grass thrive in the shade but die back from waterlogging, excess wear and tear or when exposed to dry conditions.

This is why I’ve always mixed several varieties together rather than relying on just one.

Try Groundmaster (Which I Used in 2019):

Step 6) Apply Fertiliser and Moss Control 

Fertiliser helps the grass to grow, so it covers the soil and prevents moss from gaining a foothold and there are plenty of products available, with the most recent one I tried on my lawn being seaweed extract.

Moss treatment chemicals such as iron sulphate or “no rake” products kill off any existing moss, giving the grass the freedom to grow and thrive.

If you only have a mild moss problem or your lawn is moss-free, and you want a product to prevent moss from taking hold, consider an “all in one” product such as this one from Miracle-Gro:

Step 7) Increase the Grass Cutting Height

I’ve witnessed many gardeners cut and strim their lawns as low as possible, trying to create that golf course “putting green” finish.

Unfortunately, I’ve also seen first-hand how this can cause problems.

If you cut the lawn too short, you can expect:

• Reduced photosynthesis as there’s not enough blade to absorb sufficient light.
• Roots won’t penetrate deep in the soil leading to less nutrient uptake and horizontal spread.
• More sunlight reaches the soil, drying it out in the summer, this leads to a less healthy lawn.
• More space for weeds to germinate and thrive.

In addition, many gardeners who experience issues caused by cutting the grass too short will try to compensate by using more fertilisers. This can reduce the grass root depth as the grass has no need to spread deeper to search for nutrients. 

The end result is a reduction in grass spread, density, root growth and an increase in the size of bare patches, which in turn leads to more lawn moss.

My Suggested Cutting Height

While many grass varieties can be cut short, often down to 2.5cm, I’ve had much better results in my shaded garden by letting the grass grow longer.

For shaded lawns, I suggest cutting the lawn regularly, so it’s no lower than 7.5cm in the Spring and Autumn and up to 10cm in the summer.

If you’re struggling to grow grass in the shade and you find lawn moss is taking hold, try letting your grass grow longer. I suggest experimenting with different cutting heights and finding a grass length that looks great whilst also providing enough coverage to suppress moss and weed growth.

I know from my tests that when I cut it short in the summer, it struggled to recover, and bare patches appeared, moss then took over later in the year when it was damp.

Don’t Forget The One-Third Rule

The “One Third” rule states that you should never cut over one-third of the grass blade off in one go.

This is a general rule that applies to any type of grass in any lawn in any location.

For example, if your grass is 9cm long, the rules state you shouldn’t cut it below 6cm in one go.

The tips of grass blades are the most active in photosynthesis and also give your lawn its green colour; thus, aggressive grass cutting removes the most important part of the grass blade.

Break the one-third rule and you’ll cause excessive lawn stress, this leads to poor lawn top growth, reduced root development, loss of colour and less resistance to disease and moss.

I have witnessed this first-hand in some of the gardens I worked on. The customers were letting the grass grow long and then cutting it low; due to the lack of sunlight, it struggled to recover and bare patches formed, which moss thrived in.

Step 8) Minimise Foot Traffic

Compacted soil is a perfect breeding ground for moss and algae.

You’ve probably seen this yourself; areas with heavy foot traffic often become sparse with little grass growth; moss and algae soon take over.

Common areas are:

• Near washing lines.
• Close to gates and doors.
• Along walking routes to garages, sheds and other buildings in the garden.

For shaded gardens that experience a lot of foot traffic, I’ve had good results by redesigning the layout so high-traffic lawn areas are replaced with stepping stones, paths, patios or other types of flooring that reduces the amount of foot traffic directly on the lawn.

Lawn Moss FAQs

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